Add development instructions and scripts to README.

README.md

@@ -6,3 +6,34 @@ early in development and only works on a single dance, Isaac Banner's
 ["Two Hearts in Time"](https://contradb.com/dances/2014), chosen as a
 simple dance (i.e. single progression improper, no shadow or
 next/previous neighbor interactions).
+
+
+## Development
+
+To develop locally, you need
+[TypeScript](https://www.typescriptlang.org/download/) installed. You
+can check if you have the **`tsc`** (TypeScript Compiler) command available.
+
+While developing, leave the [watch-tsc.sh](./watch-tsc.sh) script running
+or, equivalently, run the following the command from the root of the
+repository:
+```sh
+tsc --watch
+```
+
+Also, serve the `www/` directory from a local webserver.
+The [serve.sh](./serve.sh) script will do this or you can run the
+following command from the `www/` directory of the repository:
+```sh
+python -m http.server --bind localhost 8085
+```
+(Nothing special about [Python](https://www.python.org/downloads/) here,
+just the easiest web server to set up.)
+
+Then open http://localhost:8085/ in a web browser. The site should work
+in any modern browser (tested in Firefox and Chromium).
+
+Any text editor/IDE works, but I find
+[VS Code](https://code.visualstudio.com/Download)'s
+[TypeScript support](https://code.visualstudio.com/Docs/languages/typescript)
+works well.

serve.sh

@@ -0,0 +1,7 @@
+#!/bin/sh
+
+# Change directory to www/ directory.
+cd "$(dirname "$0")/www/" || exit
+echo "Serving $(pwd)"
+# From www/
+python -m http.server --bind localhost 8085

watch-tsc.sh

@@ -0,0 +1,7 @@
+#!/bin/sh
+
+# Change directory to repo root.
+cd "$(dirname "$0")" || exit
+echo "Watching $(pwd)"
+# From /
+tsc --watch

www/js/interpreter.ts

@@ -6,7 +6,7 @@ import { nameLibFigureParameters, Move, chooser_pairz } from "./libfigureMapper.
 import { LowLevelMove, SemanticAnimation, SemanticAnimationKind, animateFromLowLevelMoves } from "./lowLevelMove.js";
 import { BalanceWeight, CirclePosition, CircleSide, CircleSideOrCenter, DancerDistance, Facing, HandConnection, HandTo, LongLines, PositionKind, SemanticPosition, ShortLinesPosition, StarGrip, handToDancerToSideInCircleFacingAcross, handsFourImproper, handsInCircle, handsInLine, handsInShortLine, oppositeFacing } from "./interpreterCommon.js";
 import { ContraDBDance } from "./danceLibrary.js";
-import { errorMoveInterpreterCtor, moveInterpreters } from "./moves/_moveInterpreter.js";
+import { AllVariantsForMoveArgs, ErrorMoveInterpreter, LowLevelMovesForAllDancers, MoveAsLowLevelMovesArgs, SemanticPositionsForAllDancers, Variant, VariantCollection, errorMoveInterpreterCtor, moveInterpreters } from "./moves/_moveInterpreter.js";
 
 // Import all individual move files.
 // ls [a-z]*.js | sed 's@.*@import "./moves/\0";@'
@@ -46,73 +46,158 @@ import "./moves/turnAlone.js";
 import "./moves/upTheHall.js";
 
 
-function moveAsLowLevelMoves({ move, nextMove, startingPos, numProgessions }: { move: Move; nextMove: Move; startingPos: Map<DancerIdentity, SemanticPosition>; numProgessions: number; }): Map<DancerIdentity, LowLevelMove[]> {
+// TODO Get rid of nextMove here once variants are actually supported by Swing.
+function allVariantsForMove({ move, nextMove, startingVariants, numProgessions }: { move: Move; nextMove: Move; startingVariants: AllVariantsForMoveArgs; numProgessions: number; }): VariantCollection {
   const moveInterpreter = moveInterpreters.get(move.move) ?? errorMoveInterpreterCtor;
-  return new moveInterpreter({ move, nextMove, numProgessions }).moveAsLowLevelMoves({ startingPos });
+  return new moveInterpreter({ move, nextMove, numProgessions }).allVariantsForMove(startingVariants);
 }
 
-function danceAsLowLevelMoves(moves: Move[], startingPos: Map<DancerIdentity, SemanticPosition>): Map<DancerIdentity, LowLevelMove[]> {
-  const res = new Map<DancerIdentity, LowLevelMove[]>([...startingPos.keys()].map(id => [id, []]));
-  let currentPos = new Map<DancerIdentity, SemanticPosition>(startingPos);
+
+function danceAsLowLevelMoves(moves: Move[], startingVariants: AllVariantsForMoveArgs): Map<DancerIdentity, LowLevelMove[]> {
+  let currentVariants = new Map<string, MoveAsLowLevelMovesArgs>(startingVariants);
+  let currentVariantMoves: Map<string, LowLevelMovesForAllDancers> = new Map<string, LowLevelMovesForAllDancers>(
+    [...startingVariants.keys()].map(name => [name, new Map<DancerIdentity, LowLevelMove[]>(DancerIdentity.all().map(id => [id, []]))]));
   let numProgessions = 0;
   for (let i = 0; i < moves.length; i++) {
     const move = moves[i];
     const nextMove = i === moves.length - 1 ? moves[0] : moves[i + 1];
+
+    function updateVariants(newVariants: VariantCollection) {
+      let previousVariants = currentVariants;
+      let previousVariantMoves = currentVariantMoves;
+      try {
+        currentVariants = new Map<string, MoveAsLowLevelMovesArgs>();
+        currentVariantMoves = new Map<string, LowLevelMovesForAllDancers>();
+
+        variant: for (const [name, variant] of newVariants) {
+          const oldMoves = previousVariantMoves.get(variant.previousMoveVariant);
+          const oldPos = previousVariants.get(variant.previousMoveVariant);
+          if (!oldMoves || !oldPos) {
+            throw new Error("Referenced unknown previous variant: " + variant.previousMoveVariant);
+          }
+
+          const newMoves: LowLevelMovesForAllDancers = new Map<DancerIdentity, LowLevelMove[]>();
+          const newPositions = new Map<DancerIdentity, SemanticPosition>();
+          for (const [id, newMoveList] of variant.lowLevelMoves.entries()) {
+            const prevEnd = oldPos.startingPos.get(id)!;
+            const newStart = newMoveList[0].startPosition;
+
+            if ((prevEnd.setOffset ?? 0) != (newStart.setOffset ?? 0)
+              || (prevEnd.lineOffset ?? 0) != (newStart.lineOffset ?? 0)
+              || prevEnd.kind != newStart.kind
+              || prevEnd.which != newStart.which
+              || prevEnd.balance != newStart.balance
+              || prevEnd.dancerDistance != newStart.dancerDistance) {
+              // TODO Should this be considered a bug?
+              // TODO Require more properties to match? facing? probably not hands.
+              //throw new Error("Moves start/end did not line up.");
+              continue variant;
+            }
+
+            newMoves.set(id, [...oldMoves.get(id)!, ...newMoveList]);
+            newPositions.set(id, newMoveList.at(-1)!.endPosition);
+          }
+
+          currentVariants.set(name, { startingPos: newPositions });
+          currentVariantMoves.set(name, newMoves);
+        }
+      } catch (ex) {
+        currentVariants = previousVariants;
+        currentVariantMoves = previousVariantMoves;
+        throw ex;
+      }
+
+      if (currentVariantMoves.size === 0) {
+        currentVariants = previousVariants;
+        currentVariantMoves = previousVariantMoves;
+        throw new Error("All variants were eliminated as possibilities.");
+      }
+    }
+
     try {
       if (i > 0 && move.beats === 0 && move.move === "slide along set") {
         const slideLeft: boolean = move.parameters.slide;
-        for (const [id, currPos] of currentPos.entries()) {
+        for (const [name, currentPos] of currentVariants.entries()) {
+          for (const [id, currPos] of currentPos.startingPos.entries()) {
             const slideAmount = (currPos.which.leftRightSide() === CircleSide.Left) === slideLeft ? +0.5 : -0.5;
             const setOffset = (currPos.setOffset ?? 0) + slideAmount;
-          currentPos.set(id, { ...currPos, setOffset });
+            currentPos.startingPos.set(id, { ...currPos, setOffset });
 
-          const prevMove = res.get(id)!.at(-1)!;
+            const prevMove = currentVariantMoves.get(name)!.get(id)!.at(-1)!;
             prevMove.movementPattern.setSlideAmount = slideAmount;
             prevMove.endPosition.setOffset = setOffset;
           }
-
+        }
       } else {
-        const newMoves = moveAsLowLevelMoves({ move, nextMove, startingPos: currentPos, numProgessions });
-        for (const [id, newMoveList] of newMoves.entries()) {
-          res.get(id)!.push(...newMoveList);
-          currentPos.set(id, newMoveList.at(-1)!.endPosition);
+        const newMoves = allVariantsForMove({ move, nextMove, startingVariants: currentVariants, numProgessions });
+        if (newMoves.size === 0) {
+          updateVariants(new ErrorMoveInterpreter({ move, nextMove, numProgessions },
+            "ERROR: " + move.move + " has no valid starting variants.").allVariantsForMove(currentVariants));
+        } else {
+          updateVariants(newMoves);
+        }
+
+        if (currentVariantMoves.size === 0) {
+          throw new Error("Variants selection somehow went down to zero?");
         }
       }
     }
     catch (ex) {
+      if (currentVariantMoves.size === 0) throw ex;
+
       // catch exception so something can be displayed
-      for (const [id, pos] of currentPos.entries()) {
-        res.get(id)!.push({
-          beats: move.beats,
-          startPosition: pos,
-          endPosition: pos,
-          movementPattern: { kind: SemanticAnimationKind.StandStill },
-          move,
-          startBeat: 0,
-          interpreterError: ex instanceof Error ? ex.message : ex,
-        });
-      }
+      const errorMessage: string = ex instanceof Error ? ex.message : ex;
+      const errorVariants = new ErrorMoveInterpreter({ move, nextMove, numProgessions }, errorMessage).allVariantsForMove(currentVariants);
+      updateVariants(errorVariants);
     }
     if (move.progression) numProgessions++;
   }
 
+  // If there's multiple variants, check if there's fewer that flow into the first move.
+  if (currentVariantMoves.size !== 1) {
+    let newMoves: VariantCollection | undefined;
+    try {
+      newMoves = allVariantsForMove({ move: moves[0], nextMove: moves[1], startingVariants: currentVariants, numProgessions });
+    } catch {
+      newMoves = undefined;
+    }
+    if (newMoves) {
+      const firstMoveVariants = [...newMoves.values()].map(v => v.previousMoveVariant);
+      if (firstMoveVariants.length > 0) {
+        for (const variant of [...currentVariantMoves.keys()]) {
+          if (!firstMoveVariants.includes(variant)) {
+            currentVariantMoves.delete(variant);
+          }
+        }
+      }
+    }
+  }
+
+  const res = [...currentVariantMoves.values()].at(-1)!;
+  if (currentVariantMoves.size !== 1) {
+    res.get(DancerIdentity.OnesRobin)![0].interpreterError = "Expected exactly one variant. Found "
+            + currentVariantMoves.size + ": " + [...currentVariantMoves.keys()].join(", ");
+  }
+
   try {
     const progression = animateFromLowLevelMoves(res).progression;
     const progressionInSets = progression.y / setDistance;
 
     // fixup end positions to match start of next move
-    // TODO Handle progression.
     for (const [id, lowLevelMoves] of res.entries()) {
       for (let i = 0; i < lowLevelMoves.length - 1; i++) {
         if (!lowLevelMoves[i].endPosition) throw "endPosition is undefined";
         lowLevelMoves[i].endPosition = lowLevelMoves[i + 1].startPosition;
         if (!lowLevelMoves[i].endPosition) throw "endPosition is undefined now";
+        // TODO Exactly what is the StandStill fixup needed for? Can it be handled in other ways? Should it be rotation only?
+        /*
         if (lowLevelMoves[i].movementPattern.kind === SemanticAnimationKind.StandStill) {
           lowLevelMoves[i].startPosition = lowLevelMoves[i].endPosition;
           if (i > 0) {
             lowLevelMoves[i - 1].endPosition = lowLevelMoves[i].startPosition;
           }
         }
+        */
       }
       // If progression isn't detected properly, do nothing.
       if (progressionInSets === 0) {
@@ -134,24 +219,44 @@ function danceAsLowLevelMoves(moves: Move[], startingPos: Map<DancerIdentity, Se
   }
 }
 
+function improperShortWaves(slideTo: Hand) {
+  return new Map<DancerIdentity, SemanticPosition>([...handsFourImproper.entries()].map(
+    ([id, pos]) => ([id, {
+      kind: PositionKind.ShortLines,
+      which: pos.which.toShortLines(slideTo),
+      facing: pos.which.facingUpOrDown(),
+    }])
+  ));
+}
+
+function improperUnfoldToShortLines(center: CircleSide.Bottom | CircleSide.Top) {
+  return new Map<DancerIdentity, SemanticPosition>([...handsFourImproper.entries()].map(
+    ([id, pos]) => ([id, {
+      kind: PositionKind.ShortLines,
+      which: pos.which.unfoldToShortLines(center),
+      facing: center === CircleSide.Top ? Facing.Down : Facing.Up,
+    }])
+  ));
+}
+
+function improperLongWaves(facingOut: DanceRole) {
+  return new Map<DancerIdentity, SemanticPosition>([...handsFourImproper.entries()].map(
+    ([id, pos]) => ([id, {
+      ...pos,
+      facing: id.danceRole === facingOut ? pos.which.facingOut() : pos.which.facingAcross(),
+      hands: handsInLine({ wavy: true, which: pos.which, facing: undefined })
+    }])
+  ));
+}
+
 function StartingPosForFormation(formation: common.StartFormation, dance?: ContraDBDance): Map<DancerIdentity, SemanticPosition> {
   const preamble = dance?.preamble ?? "";
   if (preamble.includes("Starts in short waves, right hands to neighbors")) {
-    return new Map<DancerIdentity, SemanticPosition>([...handsFourImproper.entries()].map(
-      ([id, pos]) => ([id, {
-        kind: PositionKind.ShortLines,
-        which: pos.which.toShortLines(Hand.Left),
-        facing: pos.which.isTop() ? Facing.Down : Facing.Up,
-      }])
-    ));
+    return improperShortWaves(Hand.Left);
   } else if (preamble.includes("face down the hall in lines of 4, 1s splitting the 2s")) {
-    return new Map<DancerIdentity, SemanticPosition>([...handsFourImproper.entries()].map(
-      ([id, pos]) => ([id, {
-        kind: PositionKind.ShortLines,
-        which: pos.which.unfoldToShortLines(CircleSide.Top),
-        facing: Facing.Down,
-      }])
-    ));
+    return improperUnfoldToShortLines(CircleSide.Top);
+  } else if (preamble.includes("Long waves, larks face out")) {
+    return improperLongWaves(DanceRole.Lark);
   }
   
   switch (formation) {
@@ -198,6 +303,27 @@ function StartingPosForFormation(formation: common.StartFormation, dance?: Contr
   }
 }
 
+function startingVariantsForFormation(formation: common.StartFormation, dance?: ContraDBDance) : AllVariantsForMoveArgs {
+  const defaultFormation = StartingPosForFormation(formation, dance);
+  if (formation !== "improper" || defaultFormation !== handsFourImproper) {
+    return new Map<string, MoveAsLowLevelMovesArgs>([
+      ["Initial", { startingPos: defaultFormation }]
+    ]);
+  } else {
+    // Handle various different starting position that all count as "improper" like short/long waves, etc.
+    return new Map<string, MoveAsLowLevelMovesArgs>([
+      ["InitialCircle", { startingPos: handsFourImproper }],
+      ["InitialShortWavesLeft", { startingPos: improperShortWaves(Hand.Left) }],
+      ["InitialShortWavesRight", { startingPos: improperShortWaves(Hand.Right) }],
+      ["InitialShortLinesDown", { startingPos: improperUnfoldToShortLines(CircleSide.Top) }],
+      ["InitialShortLinesUp", { startingPos: improperUnfoldToShortLines(CircleSide.Bottom) }],
+      ["InitialLongWavesLarksOut", { startingPos: improperLongWaves(DanceRole.Lark) }],
+      ["InitialLongWavesRobinsOut", { startingPos: improperLongWaves(DanceRole.Robin) }],
+    ]);
+
+  }
+}
+
 export let mappedDance: Move[];
 
 export let interpretedDance: Map<DancerIdentity, LowLevelMove[]>;
@@ -205,7 +331,7 @@ export let interpretedAnimation: animation.Animation;
 
 export function loadDance(dance: ContraDBDance): animation.Animation {
   mappedDance = dance.figures.map(nameLibFigureParameters);
-  interpretedDance = danceAsLowLevelMoves(mappedDance, StartingPosForFormation(dance.start_type, dance));
+  interpretedDance = danceAsLowLevelMoves(mappedDance, startingVariantsForFormation(dance.start_type, dance));
   interpretedAnimation = animateFromLowLevelMoves(interpretedDance);
 
   return interpretedAnimation;

www/js/interpreterCommon.ts

@@ -1,4 +1,4 @@
-import { DancerIdentity, Rotation } from "./danceCommon.js";
+import { DanceRole, DancerIdentity, Rotation } from "./danceCommon.js";
 import { Hand } from "./rendererConstants.js";
 
 export enum PositionKind {
@@ -21,6 +21,14 @@ export enum CircleSide {
   Right = "Right",
 }
 export type CircleSideOrCenter = CircleSide | "Center";
+
+export function isLeftRightCircleSide(side: CircleSideOrCenter): side is CircleSide.Left | CircleSide.Right {
+  return side === CircleSide.Left || side === CircleSide.Right;
+}
+export function isTopBottomCircleSide(side: CircleSideOrCenter): side is CircleSide.Top | CircleSide.Bottom {
+  return side === CircleSide.Top || side === CircleSide.Bottom;
+}
+
 export class CirclePosition {
   public static readonly TopLeft = new CirclePosition(CirclePositionEnum.TopLeft);
   public static readonly BottomLeft = new CirclePosition(CirclePositionEnum.BottomLeft);
@@ -43,6 +51,29 @@ export class CirclePosition {
         : CirclePosition.BottomRight;
   }
 
+  public static fromSwing(side: CircleSide, swingRole: DanceRole, facing: "In" | "Out" | "Across" | Facing.Up | Facing.Down) {
+    if (isLeftRightCircleSide(side)) {
+      if (facing === Facing.Up || facing === Facing.Down) {
+        throw new Error("Ending a swing in a circle on the left/right side facing up/down doesn't make sense.");
+      } else if (facing === "Across") {
+        facing = "In";
+      }
+
+      return this.fromSides(side,
+        (side === CircleSide.Left) !== (swingRole === DanceRole.Lark) !== (facing === "In") ? CircleSide.Bottom : CircleSide.Top);
+    } else {
+      if (facing === Facing.Up || facing === Facing.Down) {
+        facing = (facing === Facing.Up) === (side === CircleSide.Top) ? "Out" : "In";
+      } else if (facing === "Across") {
+        throw new Error("Ending a swing in a circle on the top/bottom side facing across doesn't make sense.");
+      }
+
+      return this.fromSides(
+        (side === CircleSide.Top) !== (swingRole === DanceRole.Lark) !== (facing === "In") ? CircleSide.Left : CircleSide.Right,
+        side);
+    }
+  }
+
   private static enumValueToNumber(enumValue: CirclePositionEnum) : number {
     switch (enumValue) {
       case CirclePositionEnum.TopLeft:
@@ -105,6 +136,14 @@ export class CirclePosition {
     ][CirclePosition.enumValueToNumber(this.enumValue)];
   }
 
+  public swapOnSide(side: CircleSide) : CirclePosition {
+    if (side === CircleSide.Bottom || side === CircleSide.Top) {
+      return this.swapAcross();
+    } else {
+      return this.swapUpAndDown();
+    }
+  }
+
   public toShortLines(slideTo: Hand) : ShortLinesPosition {
     return slideTo === Hand.Left
       ? [
@@ -173,6 +212,28 @@ export class CirclePosition {
     return this.enumValue === CirclePositionEnum.TopLeft || this.enumValue === CirclePositionEnum.BottomRight;
   }
 
+  public isOnLeft(around: CircleSide, facing: Facing.Down | Facing.Up | Facing.Left | Facing.Right | Facing.CenterOfCircle | "Out") {
+    if (facing === Facing.CenterOfCircle) {
+      facing = facingInAround(around);
+    } else if (facing === "Out") {
+      facing = oppositeFacing(facingInAround(around));
+    }
+
+    if (around === CircleSide.Bottom || around === CircleSide.Top) {
+      if (facing === Facing.Left || facing === Facing.Right) {
+        throw new Error("Cannot face " + facing + " and have a left/right side around " + around);
+      }
+
+      return (around === CircleSide.Bottom) !== (facing === Facing.Down) !== (this.isLeft());
+    } else {
+      if (facing === Facing.Up || facing === Facing.Down) {
+        throw new Error("Cannot face " + facing + " and have a left/right side around " + around);
+      }
+
+      return (around === CircleSide.Left) !== (facing === Facing.Right) !== (this.isTop());
+    }
+  }
+
   public facingAcross() : Facing.Left | Facing.Right {
     return this.isLeft() ? Facing.Right : Facing.Left;
   }
@@ -208,6 +269,25 @@ export class ShortLinesPosition {
     this.enumValue = enumValue;
   }
 
+  public static fromSide(side: CircleSide.Left | CircleSide.Right, which: "Far" | "Middle") {
+    if (side === CircleSide.Left) {
+      return which === "Far" ? ShortLinesPosition.FarLeft : ShortLinesPosition.MiddleLeft;
+    } else {
+      return which === "Far" ? ShortLinesPosition.FarRight : ShortLinesPosition.MiddleRight;
+    }
+  }
+
+  public static fromSwing(side: "Center" | CircleSide.Left | CircleSide.Right, swingRole: DanceRole, facing: Facing.Up | Facing.Down) {
+    if (side === "Center") {
+      return this.fromSide(
+        (swingRole === DanceRole.Lark) !== (facing === Facing.Down) ? CircleSide.Right : CircleSide.Left,
+        "Middle");
+    } else {
+      return this.fromSide(side,
+        (side === CircleSide.Left) !== (swingRole === DanceRole.Lark) !== (facing === Facing.Down) ? "Far" : "Middle");
+    }
+  }
+
   private static enumValueToNumber(enumValue: ShortLinesPositionEnum) : number {
     switch (enumValue) {
       case ShortLinesPositionEnum.FarLeft:
@@ -263,13 +343,25 @@ export class ShortLinesPosition {
   }
 
   public shift(dir: Hand, facing: Facing.Up | Facing.Down): ShortLinesPosition {
-    const shift = (dir === Hand.Left) === (facing === Facing.Down) ? -1 : +1;
-    const newNum = ShortLinesPosition.enumValueToNumber(this.enumValue) + shift;
-    if (newNum < 0 || newNum > 3) {
+    const { newPos, wrap } = this.shiftWithWrap(dir, facing);
+    if (wrap) {
       throw new Error("Invalid shift: " + this + " facing " + facing + " to " + dir + ".");
     }
     
-    return ShortLinesPosition.get(ShortLinesPosition.numberToEnumValue(newNum));
+    return newPos;
+  }
+
+  public shiftWithWrap(dir: Hand, facing: Facing.Up | Facing.Down): { newPos: ShortLinesPosition, wrap?: -1 | 1 } {
+    const shift = (dir === Hand.Left) === (facing === Facing.Down) ? -1 : +1;
+    const newNum = ShortLinesPosition.enumValueToNumber(this.enumValue) + shift;
+    const newPos = ShortLinesPosition.get(ShortLinesPosition.numberToEnumValue(newNum))
+    if (newNum < 0) {
+      return { newPos, wrap: -1 };
+    } else if (newNum > 3) {
+      return { newPos, wrap: +1 };
+    } else {
+      return { newPos };
+    }
   }
 
   public isMiddle() : boolean {
@@ -295,6 +387,14 @@ export class ShortLinesPosition {
     return this.isLeft() === this.isMiddle() ? Facing.Left : Facing.Right;
   }
 
+  public facingAcross() : Facing.Left | Facing.Right {
+    return this.isLeft() ? Facing.Right : Facing.Left;
+  }
+
+  public isToLeftOf(otherPos: ShortLinesPosition): boolean {
+    return this.enumValue < otherPos.enumValue;
+  }
+
   public toString() : string {
     return this.enumValue.toString();
   }
@@ -310,7 +410,11 @@ export enum Facing {
   Left = "Left",
   Right = "Right",
 }
-export function oppositeFacing(facing: Facing.Up | Facing.Down | Facing.Left | Facing.Right | Facing.LeftInCircle | Facing.RightInCircle) {
+export function oppositeFacing(facing: Facing.Up | Facing.Down) : Facing.Up | Facing.Down;
+export function oppositeFacing(facing: Facing.Left | Facing.Right) : Facing.Left | Facing.Right;
+export function oppositeFacing(facing: Facing.LeftInCircle | Facing.RightInCircle) : Facing.LeftInCircle | Facing.RightInCircle;
+export function oppositeFacing(facing: Facing.Up | Facing.Down | Facing.Left | Facing.Right) : Facing.Up | Facing.Down | Facing.Left | Facing.Right;
+export function oppositeFacing(facing: Facing.Up | Facing.Down | Facing.Left | Facing.Right | Facing.LeftInCircle | Facing.RightInCircle) : Facing {
   switch (facing) {
     case Facing.LeftInCircle:
       return Facing.RightInCircle;
@@ -326,6 +430,25 @@ export function oppositeFacing(facing: Facing.Up | Facing.Down | Facing.Left | F
       return Facing.Left;
   }
 }
+export function isFacingUpOrDown(facing: Facing | "Across"): facing is Facing.Up | Facing.Down {
+  return facing === Facing.Up || facing === Facing.Down;
+}
+export function facingInAround(side: CircleSide) : Facing.Down | Facing.Up | Facing.Left | Facing.Right {
+  switch (side) {
+    case CircleSide.Bottom:
+      return Facing.Up;
+      break;
+    case CircleSide.Top:
+      return Facing.Down;
+      break;
+    case CircleSide.Left:
+      return Facing.Right;
+      break;
+    case CircleSide.Right:
+      return Facing.Left;
+      break;
+  }
+}
 
 export enum StarGrip {
   HandsAcross = "HandsAcross",
@@ -429,11 +552,17 @@ export const handsFourImproper: Map<DancerIdentity, SemanticPosition & { kind: P
   }],
 ]);
 
-export function handsInShortLine({ which, facing, wavy }: { which: ShortLinesPosition; facing: Facing.Up | Facing.Down; wavy: boolean; }): Map<Hand, HandConnection> {
-  return which.isMiddle() ? new Map<Hand, HandConnection>([
+export function handsInLongLines(wavy: boolean) {
+  return new Map<Hand, HandConnection>([
     [Hand.Left, { hand: wavy ? Hand.Right : Hand.Left, to: HandTo.DancerLeft }],
     [Hand.Right, { hand: wavy ? Hand.Left : Hand.Right, to: HandTo.DancerRight }],
-  ]) : new Map<Hand, HandConnection>([
+  ]);
+}
+
+export function handsInShortLine({ which, facing, wavy }: { which: ShortLinesPosition; facing: Facing.Up | Facing.Down; wavy: boolean; }): Map<Hand, HandConnection> {
+  return which.isMiddle()
+    ? handsInLongLines(wavy)
+    : new Map<Hand, HandConnection>([
       which.isLeft() === (facing === Facing.Up)
         ? [Hand.Left, { hand: wavy ? Hand.Right : Hand.Left, to: HandTo.DancerLeft }]
         : [Hand.Right, { hand: wavy ? Hand.Left : Hand.Right, to: HandTo.DancerRight }]
@@ -443,10 +572,7 @@ export function handsInLine(args: { wavy: boolean, which: ShortLinesPosition | C
   if (args.which instanceof ShortLinesPosition && (args.facing === Facing.Up || args.facing === Facing.Down)) {
     return handsInShortLine({ wavy: args.wavy, which: args.which, facing: args.facing });
   } else {
-    return new Map<Hand, HandConnection>([
-      [Hand.Left, { hand: args.wavy ? Hand.Right : Hand.Left, to: HandTo.DancerLeft }],
-      [Hand.Right, { hand: args.wavy ? Hand.Left : Hand.Right, to: HandTo.DancerRight }],
-    ]);
+    return handsInLongLines(args.wavy);
   }
 }
 export function handToDancerToSideInCircleFacingAcross(which: CirclePosition): Map<Hand, HandConnection> {
@@ -463,3 +589,93 @@ export function handToDancerToSideInCircleFacingUpOrDown(which: CirclePosition):
       : [Hand.Left, { hand: Hand.Right, to: HandTo.DancerLeft }]
   ]);
 }
+
+export function facingAdjacent(pos: SemanticPosition, otherPos: SemanticPosition): Facing | undefined {
+  if (pos.kind !== otherPos.kind) {
+    return undefined;
+  }
+
+  if (pos.kind === PositionKind.ShortLines) {
+    if (otherPos.kind !== PositionKind.ShortLines) {
+      return undefined;
+    }
+    if ((pos.setOffset ?? 0) !== (otherPos.setOffset ?? 0)) {
+      return undefined;
+    }
+    if ((pos.lineOffset ?? 0) !== (otherPos.lineOffset ?? 0)) {
+      if (pos.which === ShortLinesPosition.FarLeft && otherPos.which === ShortLinesPosition.FarRight
+          && ((pos.lineOffset ?? 0) - 1) === (otherPos.lineOffset ?? 0)) {
+        return Facing.Left;
+      } else if (pos.which === ShortLinesPosition.FarRight && otherPos.which === ShortLinesPosition.FarLeft
+          && ((pos.lineOffset ?? 0) + 1) === (otherPos.lineOffset ?? 0)) {
+        return Facing.Right;
+      } else {
+        return undefined;
+      }
+    }
+
+    if (otherPos.which.isToLeftOf(pos.which)) {
+      return Facing.Left;
+    } else {
+      return Facing.Right;
+    }
+  } else if (pos.kind === PositionKind.Circle) {
+    if (otherPos.kind !== PositionKind.Circle) {
+      return undefined;
+    }
+
+    if ((pos.lineOffset ?? 0) !== (otherPos.lineOffset ?? 0)) {
+      // TODO
+      return undefined;
+    }
+    if ((pos.setOffset ?? 0) !== (otherPos.setOffset ?? 0)) {
+      // TODO
+      return undefined;
+    }
+
+    if (pos.which.leftRightSide() === otherPos.which.leftRightSide()) {
+      if (pos.which.topBottomSide() === otherPos.which.topBottomSide()) {
+        return undefined;
+      }
+
+      if ((pos.lineOffset ?? 0) !== (otherPos.lineOffset ?? 0)) {
+        return undefined;
+      }
+
+      if ((pos.setOffset ?? 0) === (otherPos.setOffset ?? 0)) {
+        return pos.which.facingUpOrDown();
+      } else if (((pos.setOffset ?? 0) + 1) === (otherPos.setOffset ?? 0) && pos.which.isTop()) {
+        return Facing.Up;
+      } else if (((pos.setOffset ?? 0) - 1) === (otherPos.setOffset ?? 0) && !pos.which.isTop()) {
+        return Facing.Down;
+      }
+    } else if (pos.which.topBottomSide() === otherPos.which.topBottomSide()) {
+      if ((pos.setOffset ?? 0) === (otherPos.setOffset ?? 0)) {
+        return undefined;
+      }
+
+      if ((pos.lineOffset ?? 0) !== (otherPos.lineOffset ?? 0)) {
+        return pos.which.facingAcross();
+      } else if (((pos.lineOffset ?? 0) + 1) === (otherPos.lineOffset ?? 0) && pos.which.isLeft()) {
+        return Facing.Left;
+      } else if (((pos.lineOffset ?? 0) - 1) === (otherPos.lineOffset ?? 0) && !pos.which.isLeft()) {
+        return Facing.Right;
+      }
+    } else {
+      // Opposite corners of circle.
+      return undefined;
+    }
+  } else {
+    throw new Error("Unexpected PositionKind: " + otherPos.kind);
+  }
+}
+
+export function facingRequireAdjacent(pos: SemanticPosition, otherPos: SemanticPosition, moveName: string): Facing {
+  const res = facingAdjacent(pos, otherPos);
+
+  if (!res) {
+    throw new Error("Cannot " + moveName + " when not adjacent to paired dancer.");
+  }
+
+  return res;
+}

www/js/libfigureMapper.ts

@@ -34,7 +34,7 @@ type chooser_slice_return = "straight" | "diagonal" | "none";
 type chooser_all_or_center_or_outsides = "all" | "center" | "outsides";
 type chooser_down_the_hall_ender = "turn-alone" | "turn-couple" | "circle" | "cozy" | "cloverleaf" | "thread-needle" | "right-high" | "sliding-doors" | "";
 type chooser_zig_zag_ender = "" | "ring" | "allemande";
-type chooser_hey_length = "full" | "half" | "less than half" | "between half and full";
+type chooser_hey_length = "full" | "half" | "less than half" | "between half and full" | { dancer: chooser_pairz, time: 1 | 2};
 type chooser_swing_prefix = "none" | "balance" | "meltdown";
 type chooser_dancers = "everyone" | "gentlespoon" | "gentlespoons" | "ladle" | "ladles" | "partners" | "neighbors" | "ones" | "twos" | "same roles" | "first corners" | "second corners" | "first gentlespoon" | "first ladle" | "second gentlespoon" | "second ladle" | "shadows";
 type chooser_pair = "gentlespoons" | "ladles" | "ones" | "twos" | "first corners" | "second corners";
@@ -410,8 +410,21 @@ export function nameLibFigureParameters(move: LibFigureMove): Move {
     .map((v, i, a) => a.indexOf(v) === i && a.lastIndexOf(v) === i ? v : v + (a.slice(0, i).filter(el => el === v).length + 1));
   const parameters = {};
   for (let i = 0; i < parameterNames.length; i++) {
+    if (parameterNames[i] === "until") {
+      // parse chooser_hey_length
+      const hey_length: string = move.parameter_values[i];
+      if (hey_length.includes('%%')) {
+        parameters[parameterNames[i]] = {
+          dancer: hey_length.slice(0, -3),
+          time: parseInt(hey_length.at(-1)!),
+        };
+      } else {
+        parameters[parameterNames[i]] = hey_length;
+      }
+    } else {
       parameters[parameterNames[i]] = move.parameter_values[i];
     }
+  }
   const beats: number = parameters["beats"];
   parameters["beats"] = undefined;
   return {

www/js/lowLevelMove.ts

@@ -77,6 +77,8 @@ export type SemanticAnimation = {
 
   // If true, move in close while rotating.
   close: boolean,
+
+  facing?: animation.RotationAnimationFacing,
 } | {
   kind: SemanticAnimationKind.Swing,
 
@@ -292,7 +294,7 @@ function SemanticToSetPosition(semantic: SemanticPosition): DancerSetPosition {
           && (semantic.balance === BalanceWeight.Backward || semantic.balance === BalanceWeight.Forward)) {
           balanceOffset = {
             x: 0,
-            y: position.y * (
+            y: Math.sign(position.y) * (
               semantic.balance === BalanceWeight.Forward
                 ? -balanceAmount
                 : balanceAmount)
@@ -352,9 +354,9 @@ function SemanticToSetPosition(semantic: SemanticPosition): DancerSetPosition {
           case HandTo.DancerRight:
             return OffsetPlus({ x: +1, y: 0 }, balanceHandAdjustment);
           case HandTo.DancerForward:
-            const armLength = yAmount + (semantic.balance === BalanceWeight.Backward ? balanceAmount : 0);
+            const armLength = yAmount + (semantic.balance === BalanceWeight.Backward ? balanceAmount : semantic.balance === BalanceWeight.Forward ? -balanceAmount : 0);
             if (hand === connection.hand) {
-              return { x: 0, y: +armLength/2 };
+              return { x: 0, y: +armLength };
             } else {
               return { x: dancerWidth / 2 * (hand === Hand.Left ? -1 : +1), y: +armLength };
             }
@@ -655,7 +657,7 @@ function animateLowLevelMoveWithoutSlide(move: LowLevelMove): animation.Animatio
                 width: 1,
                 height: 1,
               },
-              facing: animation.RotationAnimationFacing.Forward,
+              facing: move.movementPattern.facing ?? animation.RotationAnimationFacing.Forward,
               closer: move.movementPattern.close ? {
                 transitionBeats: 1,
                 minDistance: 1,

www/js/main.ts

@@ -421,6 +421,46 @@ displaySettingsDiv.appendChild(document.createElement('br'));
 displaySettingsDiv.appendChild(extraLinesLabel);
 displaySettingsDiv.appendChild(extraLinesSelector);
 
+const trailIncrementsSelector = document.createElement('input');
+trailIncrementsSelector.type = 'number';
+trailIncrementsSelector.min = '0';
+trailIncrementsSelector.step = '1';
+trailIncrementsSelector.value = r.trailIncrements!.toString();
+trailIncrementsSelector.id = 'trailIncrements';
+trailIncrementsSelector.style.width = '3em';
+trailIncrementsSelector.addEventListener('input', (ev) => {
+  r.trailIncrements = trailIncrementsSelector.valueAsNumber;
+  drawAtCurrentBeat();
+  restartAnimation(false);
+})
+const trailIncrementsLabel = document.createElement('label');
+trailIncrementsLabel.innerText = '# trails (faded previous positions): ';
+trailIncrementsLabel.htmlFor = 'trailIncrements';
+
+displaySettingsDiv.appendChild(document.createElement('br'));
+displaySettingsDiv.appendChild(trailIncrementsLabel);
+displaySettingsDiv.appendChild(trailIncrementsSelector);
+
+const trailBeatsSelector = document.createElement('input');
+trailBeatsSelector.type = 'number';
+trailBeatsSelector.min = '0';
+trailBeatsSelector.step = '0.1';
+trailBeatsSelector.value = r.trailLengthInBeats!.toPrecision(1);
+trailBeatsSelector.id = 'trailBeats';
+trailBeatsSelector.style.width = '3em';
+trailBeatsSelector.addEventListener('input', (ev) => {
+  r.trailLengthInBeats = trailBeatsSelector.valueAsNumber;
+  drawAtCurrentBeat();
+  restartAnimation(false);
+})
+const trailBeatsLabel = document.createElement('label');
+trailBeatsLabel.innerText = '# max age of trails (faded previous positions) in beats: ';
+trailBeatsLabel.htmlFor = 'trailBeats';
+
+displaySettingsDiv.appendChild(document.createElement('br'));
+displaySettingsDiv.appendChild(trailBeatsLabel);
+displaySettingsDiv.appendChild(trailBeatsSelector);
+
 displaySettingsDiv.appendChild(document.createElement('br'));
 displaySettingsDiv.appendChild(debugRender);
 displaySettingsDiv.appendChild(debugRenderLabel);

www/js/moves/_moveInterpreter.ts

@@ -1,5 +1,5 @@
 import { CoupleRole, DanceRole, DancerIdentity, ExtendedDancerIdentity } from "../danceCommon.js";
-import { CirclePosition, CircleSideOrCenter, PositionKind, SemanticPosition } from "../interpreterCommon.js";
+import { BalanceWeight, CirclePosition, CircleSideOrCenter, DancerDistance, LongLines, PositionKind, SemanticPosition } from "../interpreterCommon.js";
 import { Move, chooser_pairz } from "../libfigureMapper.js";
 import { LowLevelMove, SemanticAnimation, SemanticAnimationKind } from "../lowLevelMove.js";
 
@@ -9,7 +9,7 @@ export const moveInterpreters: Map<MoveName, MoveInterpreterCtor<MoveName>> = ne
 
 export interface MoveInterpreterCtorArgs<N extends MoveName> {
   move: Move & { move: N };
-  nextMove: Move;
+  nextMove?: Move;
   numProgessions: number;
 }
 export type SemanticPositionsForAllDancers = Map<DancerIdentity, SemanticPosition>;
@@ -18,11 +18,13 @@ export interface MoveAsLowLevelMovesArgs {
 }
 export type LowLevelMovesForAllDancers = Map<DancerIdentity, LowLevelMove[]>;
 export interface Variant {
-  previousMoveVariant?: string,
+  previousMoveVariant: string,
   lowLevelMoves: LowLevelMovesForAllDancers,
 };
 export type VariantCollection = Map<string, Variant>;
 
+export type AllVariantsForMoveArgs = Map<string, MoveAsLowLevelMovesArgs>;
+
 export type PartialLowLevelMove = {
   remarks?: string,
   beats: number,
@@ -32,8 +34,7 @@ export type PartialLowLevelMove = {
 };
 
 export interface ISingleVariantMoveInterpreter {
-  moveAsLowLevelMoves: () => LowLevelMovesForAllDancers;
-  moveAsVariants: () => VariantCollection;
+  moveAsVariants: (previousMoveVariant: string | undefined) => VariantCollection;
 };
 
 export abstract class SingleVariantMoveInterpreter<T extends MoveInterpreter<N>, N extends MoveName> implements ISingleVariantMoveInterpreter {
@@ -43,17 +44,38 @@ export abstract class SingleVariantMoveInterpreter<T extends MoveInterpreter<N>,
   constructor(moveInterpreter: T, startingPos: SemanticPositionsForAllDancers) {
     this.moveInterpreter = moveInterpreter;
     this.startingPos = startingPos;
+
+    const checkDistance = !this.moveInterpreter.allowStartingClose();
+    const checkBalance = !this.moveInterpreter.allowStartingBalance();
+    const checkLongLines = !this.moveInterpreter.allowStartingLongLines();
+    if (checkBalance || checkDistance || checkLongLines) {
+      for (const [id, startPos] of this.startingPos) {
+        if (checkBalance && startPos.balance) {
+          throw new Error("Can not start " + this.move.move + " with balance weight " + startPos.balance);
+        }
+        if (checkDistance && startPos.dancerDistance && startPos.dancerDistance !== DancerDistance.Normal) {
+          throw new Error("Can not start " + this.move.move + " at dancerDistance " + startPos.dancerDistance);
+        }
+        if (checkLongLines && startPos.longLines) {
+          throw new Error("Can not start " + this.move.move + " at long lines " + startPos.longLines);
+        }
+      }
+    }
   }
 
   get move() : Move & { move: N } {
     return this.moveInterpreter.move;
   }
 
-  abstract moveAsLowLevelMoves(): LowLevelMovesForAllDancers;
+  moveAsLowLevelMoves(): LowLevelMovesForAllDancers {
+    throw new Error("You must implement either moveAsLowLevelMoves() or moveAsVariants().");
+  }
 
-  moveAsVariants(): VariantCollection {
+  // TODO It would make more sense for previousMoveVariant to get passed into the constructor...
+  //      ... but that requires touching every subclass, so it's an annoying refactor.
+  moveAsVariants(previousMoveVariant: string): VariantCollection {
     return new Map<string, Variant>([
-      ["default", { lowLevelMoves: this.moveAsLowLevelMoves() }]
+      ["default", { lowLevelMoves: this.moveAsLowLevelMoves(), previousMoveVariant }]
     ]);
   }
 
@@ -293,10 +315,10 @@ export abstract class SingleVariantMoveInterpreter<T extends MoveInterpreter<N>,
     } : undefined);
   }
 
-  errorStandStill() {
+  errorStandStill(error?: string) {
     return this.handleMove(({ startPos }) => {
       return [{
-        interpreterError: "UNKNOWN MOVE '" + this.move.move + "': standing still",
+        interpreterError: error ?? ("UNKNOWN MOVE '" + this.move.move + "': standing still"),
         move: this.move,
         startBeat: 0,
         beats: this.move.beats,
@@ -312,7 +334,7 @@ export abstract class SingleVariantMoveInterpreter<T extends MoveInterpreter<N>,
 
 export abstract class MoveInterpreter<N extends MoveName> {
   public readonly move: Move & { move: N };
-  public readonly nextMove: Move;
+  public readonly nextMove?: Move;
   public readonly numProgressions: number;
 
   constructor({ move, nextMove, numProgessions }: MoveInterpreterCtorArgs<N>) {
@@ -321,21 +343,97 @@ export abstract class MoveInterpreter<N extends MoveName> {
     this.numProgressions = numProgessions;
   }
 
+  allowStartingClose(): boolean {
+    // Swings can end close, but most moves can't start close, so do this check by default for all moves.
+    return false;
+  }
+
+  allowStartingBalance(): boolean {
+    // Make moves that support balance beforehand explicitly opt-in.
+    return false;
+  }
+
+  allowStartingLongLines(): boolean {
+    // Long lines is used for tweaking positioning; most moves don't know about it.
+    return false;
+  }
+
   abstract buildSingleVariantMoveInterpreter(startingPos: SemanticPositionsForAllDancers): ISingleVariantMoveInterpreter;
 
-  moveAsLowLevelMoves({ startingPos }: MoveAsLowLevelMovesArgs): LowLevelMovesForAllDancers {
-    return this.buildSingleVariantMoveInterpreter(startingPos).moveAsLowLevelMoves();
+  // TODO Better name?
+  moveAsVariants({ startingPos }: MoveAsLowLevelMovesArgs, previousMoveVariant: string): VariantCollection {
+    return this.buildSingleVariantMoveInterpreter(startingPos).moveAsVariants(previousMoveVariant);
+  }
+
+  allVariantsForMove(args: AllVariantsForMoveArgs): VariantCollection {
+    const res = new Map<string, Variant>();
+    let error;
+
+    for (const [variantName, variantArgs] of args.entries()) {
+      let newVariants: VariantCollection;
+      try {
+        newVariants = this.moveAsVariants(variantArgs, variantName);
+      } catch (ex) {
+        // TODO Maybe have a way to distinguish invalid start from error processing move?
+        error = ex;
+        // If this variant can't be processed, just continue.
+        continue;
+      }
+
+      for (const [newVariantName, variant] of newVariants) {
+        let combinedVariantName: string;
+        if (args.size === 1) {
+          combinedVariantName = newVariantName;
+        } else if (newVariants.size === 1) {
+          combinedVariantName = variantName;
+        } else {
+          combinedVariantName = newVariantName + "_from_" + variantName;
+        }
+
+        res.set(combinedVariantName, variant);
+      }
+    }
+
+    if (res.size === 0) throw error;
+    else if (res.size > 1) {
+      // TODO Try to reduce variants if possible.
+      // XXX TODO Simple hack: perfer starting improper in a circle.
+      if ([...res.values()].find(v => v.previousMoveVariant === "InitialCircle")) {
+        for (const key of [...res.entries()].filter(([k, v]) => v.previousMoveVariant !== "InitialCircle").map(([k, v]) => k)) {
+          res.delete(key);
+        }
+      }
+    }
+    return res;
   }
 }
 
-class DefaultSingleVariantMoveInterpreter extends SingleVariantMoveInterpreter<DefaultMoveInterpreter, MoveName> {
+class ErrorSingleVariantMoveInterpreter extends SingleVariantMoveInterpreter<ErrorMoveInterpreter, MoveName> {
   moveAsLowLevelMoves(): LowLevelMovesForAllDancers {
-    return this.errorStandStill();
+    return this.errorStandStill(this.moveInterpreter.error);
   }
 }
-class DefaultMoveInterpreter extends MoveInterpreter<MoveName> {
+export class ErrorMoveInterpreter extends MoveInterpreter<MoveName> {
+  public readonly error?: string;
+
+  constructor(args: MoveInterpreterCtorArgs<MoveName>, error?: string) {
+    super(args);
+    this.error = error;
+  }
+
+  override allowStartingBalance(): boolean {
+    return true;
+  }
+  override allowStartingClose(): boolean {
+    return true;
+  }
+  override allowStartingLongLines(): boolean {
+    return true;
+  }
+
   buildSingleVariantMoveInterpreter(startingPos: SemanticPositionsForAllDancers): ISingleVariantMoveInterpreter {
-    throw new Error("Method not implemented.");
+    //throw new Error("Method not implemented.");
+    return new ErrorSingleVariantMoveInterpreter(this, startingPos);
   }
 }
-export const errorMoveInterpreterCtor: MoveInterpreterCtor<MoveName> = DefaultMoveInterpreter;
+export const errorMoveInterpreterCtor: MoveInterpreterCtor<MoveName> = ErrorMoveInterpreter;Error

www/js/moves/allemande.ts

@@ -1,7 +1,7 @@
-import { SemanticPosition, PositionKind, CircleSide, Facing, CirclePosition, LongLines, HandConnection } from "../interpreterCommon.js";
+import { SemanticPosition, PositionKind, CircleSide, Facing, CirclePosition, LongLines, HandConnection, DancerDistance } from "../interpreterCommon.js";
 import { SemanticAnimationKind } from "../lowLevelMove.js";
 import { Hand } from "../rendererConstants.js";
-import { ISingleVariantMoveInterpreter, LowLevelMovesForAllDancers, MoveInterpreter, SemanticPositionsForAllDancers, SingleVariantMoveInterpreter, moveInterpreters } from "./_moveInterpreter.js";
+import { ISingleVariantMoveInterpreter, LowLevelMovesForAllDancers, MoveInterpreter, MoveInterpreterCtorArgs, SemanticPositionsForAllDancers, SingleVariantMoveInterpreter, moveInterpreters } from "./_moveInterpreter.js";
 
 type allemandeMoves = "allemande" | "allemande orbit" | "gyre";
 
@@ -10,32 +10,36 @@ class AllemandeSingleVariant extends SingleVariantMoveInterpreter<Allemande, all
     // Need to store this locally so checking move.move restricts move.parameters.
     const move = this.move;
 
-    const allemandeCircling = move.move === "allemande orbit" ? move.parameters.circling1 : move.parameters.circling;
-    const byHandOrShoulder = (move.move === "gyre" ? move.parameters.shoulder : move.parameters.hand) ? Hand.Right : Hand.Left;
-
-    // TODO Not sure if this is right.
-    const swap = allemandeCircling % 360 === 180;
-    const returnToStart = allemandeCircling % 360 === 0;
-    const intoWave = !swap && !returnToStart && allemandeCircling % 90 == 0;
-    const intoWavePositions = !intoWave ? 0 : (allemandeCircling % 360 === 90) === (byHandOrShoulder === Hand.Left) ? 1 : -1;
-    if (!swap && !returnToStart && !intoWave) {
-      // TODO Support allemande that's not a swap or no-op.
-      throw "Unsupported allemande circle amount: " + allemandeCircling;
+    for (const [id, pos] of this.startingPos.entries()) {
+      if (this.findPairOpposite(this.move.parameters.who, id) === null) {
+        if (pos.dancerDistance && pos.dancerDistance !== DancerDistance.Normal) {
+          throw new Error("Dancers not involved in allemande must start at normal dancer distance.");
+        }
+        if (pos.longLines) {
+          throw new Error("Dancers not involved in allemande must start not in long lines.");
+        }
+      }
     }
 
-    return this.handlePairedMove(move.parameters.who, ({ startPos, around, withId, withPos }) => {
-      let endPosition: SemanticPosition = startPos;
-      let startingPos = startPos;
-      if (swap) {
+    return this.handlePairedMove(this.move.parameters.who, ({ startPos, around, withId, withPos }) => {
+      if (startPos.kind === PositionKind.ShortLines && withPos.kind === PositionKind.ShortLines
+          && startPos.which.leftRightSide() != withPos.which.leftRightSide()
+          && (!startPos.which.isMiddle() || !withPos.which.isMiddle())) {
+        throw new Error("Allemande in short lines must either be on same side of set or in the middle.");
+      }
+
+      let endPosition: SemanticPosition = {...startPos, dancerDistance: undefined, longLines: undefined, balance: undefined };
+      let startingPos = {...startPos };
+      if (this.moveInterpreter.swap) {
         // TODO This was more complicated. Is this wrong?
-        endPosition = withPos;
-      } else if (intoWave) {
+        endPosition = {...withPos, dancerDistance: undefined, longLines: undefined, balance: undefined };
+      } else if (this.moveInterpreter.intoWave) {
         if (startPos.kind === PositionKind.ShortLines) {
           if (around === CircleSide.Left || around === CircleSide.Right) {
             // Fix startPos if necessary. Needed because pass through always swaps but sometimes shouldn't.
             let startWhich = startPos.which;
             if ((startPos.facing === Facing.Up || startPos.facing === Facing.Down) &&
-              ((byHandOrShoulder === Hand.Right)
+              ((this.moveInterpreter.byHandOrShoulder === Hand.Right)
                 !== (startPos.facing === Facing.Up)
                 !== startPos.which.isLeftOfSide())) {
               startWhich = startPos.which.swapOnSide()
@@ -47,14 +51,14 @@ class AllemandeSingleVariant extends SingleVariantMoveInterpreter<Allemande, all
 
             const endWhich = CirclePosition.fromSides(startingPos.which.leftRightSide(),
               startWhich.isLeftOfSide()
-                !== (byHandOrShoulder === Hand.Right)
-                !== (intoWavePositions === 1)
+                !== (this.moveInterpreter.byHandOrShoulder === Hand.Right)
+                !== (this.moveInterpreter.intoWavePositions === 1)
                 ? CircleSide.Top
                 : CircleSide.Bottom);
             endPosition = {
               kind: PositionKind.Circle,
               which: endWhich,
-              facing: (startingPos.facing === Facing.Up) === (intoWavePositions === 1)
+              facing: (startingPos.facing === Facing.Up) === (this.moveInterpreter.intoWavePositions === 1)
                 ? endWhich.facingAcross()
                 : endWhich.facingOut(),
               setOffset: startingPos.setOffset,
@@ -66,7 +70,7 @@ class AllemandeSingleVariant extends SingleVariantMoveInterpreter<Allemande, all
         } else {
           if (around === "Center") {
             const startCenter = startPos.longLines === LongLines.Center;
-            const endWhich = startPos.which.circleRight(intoWavePositions);
+            const endWhich = startPos.which.circleRight(this.moveInterpreter.intoWavePositions);
             endPosition = {
               kind: PositionKind.Circle,
               which: endWhich,
@@ -76,11 +80,11 @@ class AllemandeSingleVariant extends SingleVariantMoveInterpreter<Allemande, all
               lineOffset: startPos.lineOffset,
             }
           } else {
-            const endWhich = startPos.which.toShortLines(intoWavePositions === 1 ? Hand.Right : Hand.Left);
+            const endWhich = startPos.which.toShortLines(this.moveInterpreter.intoWavePositions === 1 ? Hand.Right : Hand.Left);
             endPosition = {
               kind: PositionKind.ShortLines,
               which: endWhich,
-              facing: endWhich.isLeftOfSide() === (byHandOrShoulder === Hand.Left) ? Facing.Up : Facing.Down,
+              facing: endWhich.isLeftOfSide() === (this.moveInterpreter.byHandOrShoulder === Hand.Left) ? Facing.Up : Facing.Down,
               setOffset: startPos.setOffset,
               lineOffset: startPos.lineOffset,
             }
@@ -90,30 +94,23 @@ class AllemandeSingleVariant extends SingleVariantMoveInterpreter<Allemande, all
 
       return this.combine([
         {
-          beats: move.beats,
+          beats: this.move.beats,
           endPosition,
           movementPattern: {
             kind: SemanticAnimationKind.RotateAround,
-            minAmount: byHandOrShoulder === Hand.Right ? allemandeCircling : -allemandeCircling,
+            minAmount: this.moveInterpreter.byHandOrShoulder === Hand.Right ? this.moveInterpreter.allemandeCircling : -this.moveInterpreter.allemandeCircling,
             around,
-            byHand: move.move === "allemande" || move.move === "allemande orbit" ? byHandOrShoulder : undefined,
+            byHand: move.move === "allemande" || move.move === "allemande orbit" ? this.moveInterpreter.byHandOrShoulder : undefined,
             close: true,
           },
         },
       ], {
         ...startingPos,
         hands: startPos.hands && move.move !== "gyre"
-          ? new Map<Hand, HandConnection>([...startPos.hands.entries()].filter(([h, c]) => h === byHandOrShoulder))
+          ? new Map<Hand, HandConnection>([...startPos.hands.entries()].filter(([h, c]) => h === this.moveInterpreter.byHandOrShoulder))
           : undefined
       });
     }, move.move !== "allemande orbit" ? undefined : ({ id, startPos }) => {
-      const orbitAmount = move.parameters.circling2;
-      const swap = orbitAmount % 360 === 180;
-      if (!swap && orbitAmount % 360 !== 0) {
-        // TODO Support allemande that's not a swap or no-op.
-        throw "Unsupported allemande orbit amount: " + orbitAmount;
-      }
-
       const startingPos: SemanticPosition = {
         ...startPos,
         hands: undefined,
@@ -121,7 +118,7 @@ class AllemandeSingleVariant extends SingleVariantMoveInterpreter<Allemande, all
         dancerDistance: undefined,
       }
       let endPosition: SemanticPosition;
-      if (swap) {
+      if (this.moveInterpreter.orbitSwap) {
         if (startingPos.kind === PositionKind.Circle) {
           endPosition =
           {
@@ -148,7 +145,7 @@ class AllemandeSingleVariant extends SingleVariantMoveInterpreter<Allemande, all
           movementPattern: {
             kind: SemanticAnimationKind.RotateAround,
             // Orbit is opposite direction of allemande.
-            minAmount: byHandOrShoulder === Hand.Right ? -orbitAmount : +orbitAmount,
+            minAmount: this.moveInterpreter.byHandOrShoulder === Hand.Right ? -this.moveInterpreter.orbitCircling : +this.moveInterpreter.orbitCircling,
             around: "Center",
             byHand: undefined,
             close: false,
@@ -160,6 +157,55 @@ class AllemandeSingleVariant extends SingleVariantMoveInterpreter<Allemande, all
 }
 
 class Allemande extends MoveInterpreter<allemandeMoves> {
+  public readonly allemandeCircling: number;
+  public readonly orbitCircling: number;
+  public readonly byHandOrShoulder: Hand;
+  public readonly swap: boolean;
+  public readonly orbitSwap: boolean;
+  public readonly returnToStart: boolean;
+  public readonly intoWave: boolean;
+  public readonly intoWavePositions: number;
+
+  constructor(args: MoveInterpreterCtorArgs<allemandeMoves>) {
+    super(args);
+
+    this.allemandeCircling = this.move.move === "allemande orbit" ? this.move.parameters.circling1 : this.move.parameters.circling;
+    this.byHandOrShoulder = (this.move.move === "gyre" ? this.move.parameters.shoulder : this.move.parameters.hand) ? Hand.Right : Hand.Left;
+
+    // TODO Not sure if this is right.
+    this.swap = this.allemandeCircling % 360 === 180;
+    this.returnToStart = this.allemandeCircling % 360 === 0;
+    this.intoWave = !this.swap && !this.returnToStart && this.allemandeCircling % 90 == 0;
+    this.intoWavePositions = !this.intoWave
+      ? 0
+      : (this.allemandeCircling % 360 === 90) === (this.byHandOrShoulder === Hand.Left)
+        ? +1
+        : -1;
+    if (!this.swap && !this.returnToStart && !this.intoWave) {
+      // TODO Support allemande that's not a swap or no-op.
+      throw "Unsupported allemande circle amount: " + this.allemandeCircling;
+    }
+
+    if (this.move.move === "allemande orbit") {
+      this.orbitCircling = this.move.parameters.circling2;
+      this.orbitSwap = this.orbitCircling % 360 === 180;
+      if (!this.orbitSwap && this.orbitCircling % 360 !== 0) {
+        // TODO Support allemande that's not a swap or no-op.
+        throw "Unsupported allemande orbit amount: " + this.orbitCircling;
+      }
+    } else {
+      this.orbitCircling = 0;
+      this.orbitSwap = false;
+    }
+  }
+
+  override allowStartingClose(): boolean {
+    return true;
+  }
+  override allowStartingLongLines(): boolean {
+    return true;
+  }
+
   buildSingleVariantMoveInterpreter(startingPos: SemanticPositionsForAllDancers): ISingleVariantMoveInterpreter {
     return new AllemandeSingleVariant(this, startingPos);
   }

www/js/moves/balance.ts

@@ -1,39 +1,100 @@
-import { BalanceWeight } from "../interpreterCommon.js";
+import { BalanceWeight, Facing, HandConnection, HandTo, PositionKind, facingAdjacent, facingRequireAdjacent } from "../interpreterCommon.js";
 import { SemanticAnimationKind } from "../lowLevelMove.js";
-import { ISingleVariantMoveInterpreter, LowLevelMovesForAllDancers, MoveInterpreter, MoveInterpreterCtorArgs, SemanticPositionsForAllDancers, SingleVariantMoveInterpreter, moveInterpreters } from "./_moveInterpreter.js";
+import { Hand } from "../rendererConstants.js";
+import { ISingleVariantMoveInterpreter, LowLevelMovesForAllDancers, MoveInterpreter, MoveInterpreterCtorArgs, SemanticPositionsForAllDancers, SingleVariantMoveInterpreter, Variant, VariantCollection, moveInterpreters } from "./_moveInterpreter.js";
 
-class BalanceSingleVariant extends SingleVariantMoveInterpreter<Balance, "balance"> {
-  moveAsLowLevelMoves(): LowLevelMovesForAllDancers {
+const moveName = "balance";
+
+class BalanceSingleVariant extends SingleVariantMoveInterpreter<Balance, typeof moveName> {
+  private static readonly balanceOptions : [BalanceWeight, BalanceWeight | undefined, Hand | undefined][]= [
+    // TODO Any others?
+    [BalanceWeight.Forward, undefined, undefined],
+    [BalanceWeight.Forward, BalanceWeight.Backward, undefined],
+    // TODO Should be left/right/inside/outside hands?
+    [BalanceWeight.Forward, BalanceWeight.Backward, Hand.Left],
+    [BalanceWeight.Forward, BalanceWeight.Backward, Hand.Right],
+    [BalanceWeight.Right, BalanceWeight.Backward, undefined],
+    [BalanceWeight.Right, BalanceWeight.Left, undefined],
+    [BalanceWeight.Left, BalanceWeight.Right, undefined],
+  ];
+
+  moveAsVariants(previousMoveVariant: string): VariantCollection {
+    const res = new Map<string, Variant>();
+
+    for (const [firstWeight, secondWeight, hand] of BalanceSingleVariant.balanceOptions) {
+      // If balancing someone, need to know by which hand.
+      if ((hand === undefined) !== (this.move.parameters.who === "everyone")) continue;
+      try {
+        res.set((firstWeight?.toString() ?? "") + (secondWeight?.toString() ?? "") + (hand === undefined ? "" : hand.toString() + "Hand"), {
+          lowLevelMoves: this.moveAsLowLevelMovesWeights(firstWeight, secondWeight, hand),
+          previousMoveVariant
+        });
+      }
+      catch { }
+    }
+
+    return res;
+  }
+
+  moveAsLowLevelMovesWeights(firstWeight?: BalanceWeight, secondWeight?: BalanceWeight, hand?: Hand): LowLevelMovesForAllDancers {
+    if (this.move.parameters.who !== "everyone") {
+      return this.handlePairedMove(this.move.parameters.who, ({ startPos, withPos }) => {
+        // TODO Does this need to support balancing inside/outside hands? If so how to identify them?
+        const hands = hand === undefined ? startPos.hands : new Map<Hand, HandConnection>([[hand, {hand, to: HandTo.DancerForward}]]);
+
+        const facing = facingRequireAdjacent(startPos, withPos, this.move.move);
+
+        const startingPos = {...startPos, facing, hands};
+
+        return this.combine([
+          {
+            beats: this.moveInterpreter.balancePartBeats,
+            endPosition: { ...startingPos, balance: firstWeight, hands },
+            movementPattern: { kind: SemanticAnimationKind.Linear },
+          },
+          {
+            beats: this.moveInterpreter.balancePartBeats,
+            endPosition: { ...startingPos, balance: secondWeight, hands },
+            movementPattern: { kind: SemanticAnimationKind.Linear },
+          },
+        ], startingPos);
+      });
+    } else {
       return this.handleMove(({ startPos }) => {
         // TODO Use who to determine facing?
         // TODO Could be left to right, not back and forth?
         // TODO How to determine hand... by next move, I guess?
+        if (startPos.kind === PositionKind.Circle && startPos.facing === Facing.CenterOfCircle) {
+          if (firstWeight === BalanceWeight.Left || firstWeight === BalanceWeight.Right || firstWeight === BalanceWeight.Backward
+            || secondWeight === BalanceWeight.Left || secondWeight === BalanceWeight.Right || secondWeight === BalanceWeight.Backward) {
+            throw new Error("Balancing left or right in a circle is unsupported.");
+          }
+        }
 
         return this.combine([
           {
-          beats: this.moveInterpreter.forwardBeats,
-          endPosition: { ...startPos, balance: BalanceWeight.Forward },
+            beats: this.moveInterpreter.balancePartBeats,
+            endPosition: { ...startPos, balance: firstWeight },
             movementPattern: { kind: SemanticAnimationKind.Linear },
           },
           {
-          beats: this.moveInterpreter.backwardBeats,
-          endPosition: { ...startPos, balance: BalanceWeight.Backward },
+            beats: this.moveInterpreter.balancePartBeats,
+            endPosition: { ...startPos, balance: secondWeight },
             movementPattern: { kind: SemanticAnimationKind.Linear },
           },
         ], startPos);
       });
     }
+  }
 }
 
-class Balance extends MoveInterpreter<"balance"> {
-  public readonly forwardBeats: number;
-  public readonly backwardBeats: number;
+class Balance extends MoveInterpreter<typeof moveName> {
+  public readonly balancePartBeats: number;
 
-  constructor(args: MoveInterpreterCtorArgs<"balance">) {
+  constructor(args: MoveInterpreterCtorArgs<typeof moveName>) {
     super(args);
 
-    this.forwardBeats = this.move.beats / 2;
-    this.backwardBeats = this.move.beats - this.forwardBeats;
+    this.balancePartBeats = this.move.beats / 2;
   }
 
   buildSingleVariantMoveInterpreter(startingPos: SemanticPositionsForAllDancers): ISingleVariantMoveInterpreter {
@@ -41,4 +102,4 @@ class Balance extends MoveInterpreter<"balance"> {
   }
 }
 
-moveInterpreters.set("balance", Balance);
+moveInterpreters.set(moveName, Balance);

www/js/moves/balanceTheRing.ts

@@ -1,4 +1,4 @@
-import { BalanceWeight, Facing, HandConnection, HandTo, PositionKind, SemanticPosition } from "../interpreterCommon.js";
+import { BalanceWeight, Facing, HandConnection, HandTo, PositionKind, SemanticPosition, handsInCircle } from "../interpreterCommon.js";
 import { Move } from "../libfigureMapper.js";
 import { LowLevelMove, SemanticAnimationKind } from "../lowLevelMove.js";
 import { Hand } from "../rendererConstants.js";
@@ -11,14 +11,11 @@ export function balanceCircleInAndOut(move: Move, startPos: SemanticPosition, ba
   }
 
   balanceBeats ??= 4;
-  const balancePartBeats = balanceBeats/2;
+  const balancePartBeats = balanceBeats / 2;
 
   const holdingHandsInCircle: SemanticPosition = {...startPos,
     facing: Facing.CenterOfCircle,
-    hands: new Map<Hand, HandConnection>([
-      [Hand.Left, { hand: Hand.Right, to: HandTo.LeftInCircle }],
-      [Hand.Right, { hand: Hand.Left, to: HandTo.RightInCircle }],
-    ]),
+    hands: handsInCircle,
   };
   const circleBalancedIn: SemanticPosition = {...holdingHandsInCircle,
     balance: BalanceWeight.Forward,

www/js/moves/boxCirculate.ts

@@ -1,14 +1,30 @@
 import { DanceRole, CoupleRole } from "../danceCommon.js";
-import { SemanticPosition, Facing, HandConnection, HandTo, BalanceWeight } from "../interpreterCommon.js";
+import { SemanticPosition, Facing, HandConnection, HandTo, BalanceWeight, handsInLine, LongLines } from "../interpreterCommon.js";
 import { Move } from "../libfigureMapper.js";
 import { SemanticAnimationKind } from "../lowLevelMove.js";
 import { Hand } from "../rendererConstants.js";
-import { ISingleVariantMoveInterpreter, LowLevelMovesForAllDancers, MoveInterpreter, PartialLowLevelMove, SemanticPositionsForAllDancers, SingleVariantMoveInterpreter, moveInterpreters } from "./_moveInterpreter.js";
+import { ISingleVariantMoveInterpreter, LowLevelMovesForAllDancers, MoveInterpreter, PartialLowLevelMove, SemanticPositionsForAllDancers, SingleVariantMoveInterpreter, Variant, VariantCollection, moveInterpreters } from "./_moveInterpreter.js";
 
 const moveName: Move["move"] = "box circulate";
 
 class BoxCirculateSingleVariant extends SingleVariantMoveInterpreter<BoxCirculate, typeof moveName> {
-  moveAsLowLevelMoves(): LowLevelMovesForAllDancers {
+  moveAsVariants(previousMoveVariant: string): VariantCollection {
+    const res = new Map<string, Variant>();
+
+    for (const crossPartway of (this.move.note?.includes("catch") ? [true] : [true, false])) {
+      try {
+        res.set(crossPartway ? "CrossPartway" : "Normal", {
+          lowLevelMoves: this.moveAsLowLevelMovesCross(crossPartway),
+          previousMoveVariant
+        });
+      }
+      catch { }
+    }
+
+    return res;
+  }
+
+  moveAsLowLevelMovesCross(crossPartway: boolean): LowLevelMovesForAllDancers {
     const circulateRight: boolean = this.move.parameters.hand;
     const whoCrosses = this.move.parameters.who;
     return this.handleCircleMove(({ id, startPos }) => {
@@ -34,7 +50,7 @@ class BoxCirculateSingleVariant extends SingleVariantMoveInterpreter<BoxCirculat
       // Starts in long wavy lines.
       const startingPos: SemanticPosition = {
         ...startPos,
-        facing: isCrossing === startPos.which.isLeft() ? Facing.Right : Facing.Left,
+        facing: isCrossing ? startPos.which.facingAcross() : startPos.which.facingOut(),
         hands: new Map<Hand, HandConnection>([
           [Hand.Left, { hand: Hand.Left, to: HandTo.DancerLeft }],
           [Hand.Right, { hand: Hand.Right, to: HandTo.DancerRight }],
@@ -61,6 +77,7 @@ class BoxCirculateSingleVariant extends SingleVariantMoveInterpreter<BoxCirculat
           ...startingPos,
           which: isCrossing ? startingPos.which.swapAcross() : startingPos.which.swapUpAndDown(),
           facing: isCrossing ? startingPos.facing : startingPos.facing === Facing.Right ? Facing.Left : Facing.Right,
+          longLines: isCrossing && crossPartway ? LongLines.Center : undefined,
         },
         movementPattern: {
           // TODO Not sure loop should really be linear...

www/js/moves/boxTheGnat.ts

@@ -1,44 +1,41 @@
-import { HandConnection, HandTo, BalanceWeight } from "../interpreterCommon.js";
-import { Move } from "../libfigureMapper.js";
+import { HandConnection, HandTo, BalanceWeight, facingRequireAdjacent } from "../interpreterCommon.js";
 import { SemanticAnimationKind } from "../lowLevelMove.js";
 import { Hand } from "../rendererConstants.js";
-import { ISingleVariantMoveInterpreter, LowLevelMovesForAllDancers, MoveInterpreter, PartialLowLevelMove, SemanticPositionsForAllDancers, SingleVariantMoveInterpreter, moveInterpreters } from "./_moveInterpreter.js";
+import { ISingleVariantMoveInterpreter, LowLevelMovesForAllDancers, MoveInterpreter, MoveInterpreterCtorArgs, PartialLowLevelMove, SemanticPositionsForAllDancers, SingleVariantMoveInterpreter, moveInterpreters } from "./_moveInterpreter.js";
 
-const moveName: Move["move"] = "box the gnat";
+const moveName = "box the gnat";
 
 class BoxTheGnatSingleVariant extends SingleVariantMoveInterpreter<BoxTheGnat, typeof moveName> {
   moveAsLowLevelMoves(): LowLevelMovesForAllDancers {
     return this.handlePairedMove(this.move.parameters.who, ({ startPos, around, withPos }) => {
-      const hand = this.move.parameters.hand ? Hand.Right : Hand.Left;
-      const balanceBeats = this.move.parameters.bal
-        ? this.move.beats > 4
-          ? this.move.beats - 4
-          : 2
-        : 0;
-      const balancePartBeats = balanceBeats / 2;
-      const twirlBeats = this.move.beats - balanceBeats;
+      if (startPos.hands && startPos.hands.get(Hand.Right) === undefined && startPos.hands.get(Hand.Left)?.hand === Hand.Left) {
+        throw new Error(this.move.move + " shouldn't start with holding left hands. Something went wrong.");
+      }
+      if (startPos.balance && startPos.balance !== BalanceWeight.Backward) {
+        throw new Error(this.move.move + " shouldn't start with balance weight " + startPos.balance);
+      }
 
-      // TODO Adjust facing?
-      const startPosition = { ...startPos, hands: new Map<Hand, HandConnection>([[hand, { hand, to: HandTo.DancerForward }]]) };
+      const facing = facingRequireAdjacent(startPos, withPos, this.move.move);
+      const startPosition = { ...startPos, hands: this.moveInterpreter.hands, facing };
 
       if (around === "Center") {
         throw "TwirlSwap around center is unsupported.";
       }
 
       const twirl: PartialLowLevelMove = {
-        beats: twirlBeats,
-        endPosition: withPos,
+        beats: this.moveInterpreter.twirlBeats,
+        endPosition: { ...withPos, balance: undefined },
         movementPattern: {
           kind: SemanticAnimationKind.TwirlSwap,
           around,
-          hand,
+          hand: this.moveInterpreter.hand,
         }
       };
 
       if (this.move.parameters.bal) {
         return this.combine([
           {
-            beats: balancePartBeats,
+            beats: this.moveInterpreter.balancePartBeats,
             endPosition: {
               ...startPosition,
               balance: BalanceWeight.Forward,
@@ -48,7 +45,7 @@ class BoxTheGnatSingleVariant extends SingleVariantMoveInterpreter<BoxTheGnat, t
             }
           },
           {
-            beats: balancePartBeats,
+            beats: this.moveInterpreter.balancePartBeats,
             endPosition: {
               ...startPosition,
               balance: BalanceWeight.Backward,
@@ -66,6 +63,29 @@ class BoxTheGnatSingleVariant extends SingleVariantMoveInterpreter<BoxTheGnat, t
 }
 
 class BoxTheGnat extends MoveInterpreter<typeof moveName> {
+  public readonly hand: Hand;
+  public readonly hands: Map<Hand, HandConnection>;
+  public readonly balancePartBeats: number;
+  public readonly twirlBeats: number;
+
+  constructor(args: MoveInterpreterCtorArgs<typeof moveName>) {
+    super(args);
+
+    this.hand = this.move.parameters.hand ? Hand.Right : Hand.Left;
+    this.hands = new Map<Hand, HandConnection>([[this.hand, { hand: this.hand, to: HandTo.DancerForward }]]);
+    const balanceBeats = this.move.parameters.bal
+      ? this.move.beats > 4
+        ? this.move.beats - 4
+        : this.move.beats / 2
+      : 0;
+    this.balancePartBeats = balanceBeats / 2;
+    this.twirlBeats = this.move.beats - balanceBeats;
+  }
+
+  override allowStartingBalance(): boolean {
+    return true;
+  }
+
   buildSingleVariantMoveInterpreter(startingPos: SemanticPositionsForAllDancers): ISingleVariantMoveInterpreter {
     return new BoxTheGnatSingleVariant(this, startingPos);
   }

www/js/moves/butterflyWhirl.ts

@@ -1,3 +1,4 @@
+import { RotationAnimationFacing } from "../animation.js";
 import { Move } from "../libfigureMapper.js";
 import { SemanticAnimationKind } from "../lowLevelMove.js";
 import { Hand } from "../rendererConstants.js";
@@ -14,8 +15,10 @@ class ButterflyWhirlSingleVariant extends SingleVariantMoveInterpreter<Butterfly
         movementPattern: {
           kind: SemanticAnimationKind.RotateAround,
           around: startPos.which.leftRightSide(),
-          // TODO hand around isn't the same as allemande...
           byHand: startPos.which.isOnLeftLookingAcross() ? Hand.Right : Hand.Left,
+          facing: startPos.which.isOnLeftLookingAcross()
+                    ? RotationAnimationFacing.Forward
+                    : RotationAnimationFacing.Backward,
           close: true,
           minAmount: 360,
         }
@@ -25,6 +28,10 @@ class ButterflyWhirlSingleVariant extends SingleVariantMoveInterpreter<Butterfly
 }
 
 class ButterflyWhirl extends MoveInterpreter<typeof moveName> {
+  override allowStartingClose(): boolean {
+    return true;
+  }
+
   buildSingleVariantMoveInterpreter(startingPos: SemanticPositionsForAllDancers): ISingleVariantMoveInterpreter {
     return new ButterflyWhirlSingleVariant(this, startingPos);
   }

www/js/moves/californiaTwirl.ts

@@ -1,4 +1,4 @@
-import { HandConnection, HandTo, CircleSide, Facing } from "../interpreterCommon.js";
+import { HandConnection, HandTo, CircleSide, Facing, facingInAround, oppositeFacing } from "../interpreterCommon.js";
 import { Move } from "../libfigureMapper.js";
 import { SemanticAnimationKind } from "../lowLevelMove.js";
 import { Hand } from "../rendererConstants.js";
@@ -8,10 +8,17 @@ const moveName: Move["move"] = "California twirl";
 
 class CaliforniaTwirlSingleVariant extends SingleVariantMoveInterpreter<CaliforniaTwirl, typeof moveName> {
   moveAsLowLevelMoves(): LowLevelMovesForAllDancers {
-    return this.handleCirclePairedMove(this.move.parameters.who, ({ startPos }) => {
-      // TODO does "who" matter here or is it entirely positional? At least need to know who to omit.
+    return this.handleCirclePairedMove(this.move.parameters.who, ({ startPos, around }) => {
+      if (around === "Center") {
+        throw new Error("Don't know how to " + this.move.move + " around the center.");
+      }
 
-      const onLeft: boolean = startPos.which.isOnLeftLookingUpAndDown();
+      if (startPos.facing === Facing.LeftInCircle || startPos.facing === Facing.RightInCircle) {
+        throw new Error("Don't know how to " + this.move.move + " starting facing " + startPos.facing);
+      }
+
+      const facing = startPos.facing === Facing.CenterOfCircle ? facingInAround(around) : startPos.facing;
+      const onLeft: boolean = startPos.which.isOnLeft(around, startPos.facing);
       // TODO get rid of this 1 beat set up and make it part of TwirlSwap?
       return this.combine([
         {
@@ -21,7 +28,7 @@ class CaliforniaTwirlSingleVariant extends SingleVariantMoveInterpreter<Californ
             hands: new Map<Hand, HandConnection>([onLeft
               ? [Hand.Right, { to: HandTo.DancerRight, hand: Hand.Left }]
               : [Hand.Left, { to: HandTo.DancerLeft, hand: Hand.Right }]]),
-            facing: startPos.which.topBottomSide() === CircleSide.Top ? Facing.Down : Facing.Up,
+            facing,
           },
           movementPattern: {
             kind: SemanticAnimationKind.Linear,
@@ -31,12 +38,12 @@ class CaliforniaTwirlSingleVariant extends SingleVariantMoveInterpreter<Californ
           beats: this.move.beats - 1,
           endPosition: {
             ...startPos,
-            which: startPos.which.swapAcross(),
-            facing: startPos.which.topBottomSide() === CircleSide.Top ? Facing.Up : Facing.Down,
+            which: startPos.which.swapOnSide(around),
+            facing: oppositeFacing(facing),
           },
           movementPattern: {
             kind: SemanticAnimationKind.TwirlSwap,
-            around: startPos.which.topBottomSide(),
+            around,
             hand: onLeft ? Hand.Right : Hand.Left,
           }
         }], startPos);

www/js/moves/circle.ts

@@ -1,4 +1,4 @@
-import { Facing, handsInCircle } from "../interpreterCommon.js";
+import { DancerDistance, Facing, handsInCircle } from "../interpreterCommon.js";
 import { Move } from "../libfigureMapper.js";
 import { SemanticAnimationKind } from "../lowLevelMove.js";
 import { ISingleVariantMoveInterpreter, LowLevelMovesForAllDancers, MoveInterpreter, SemanticPositionsForAllDancers, SingleVariantMoveInterpreter, moveInterpreters } from "./_moveInterpreter.js";

www/js/moves/downTheHall.ts

@@ -22,6 +22,9 @@ class DownTheHallSingleVariant extends SingleVariantMoveInterpreter<DownTheHall,
     }
     return this.handleMove(({ startPos }) => {
       const startFacing = this.move.parameters.facing === "backward" ? Facing.Up : Facing.Down;
+      if (startPos.facing !== startFacing && (startPos.facing === Facing.Up || startPos.facing === Facing.Down)) {
+        throw new Error("Started facing the wrong direction.");
+      }
       const startWhich: ShortLinesPosition = startPos.kind === PositionKind.ShortLines
         ? startPos.which
         // TODO Is this always the right way to convert circle to short lines?

www/js/moves/hey.ts

@@ -1,45 +1,18 @@
 import { DancerIdentity } from "../danceCommon.js";
 import { SemanticPosition, PositionKind, ShortLinesPosition, CirclePosition, CircleSide, Facing } from "../interpreterCommon.js";
-import { Move } from "../libfigureMapper.js";
 import { LowLevelMove, SemanticAnimationKind } from "../lowLevelMove.js";
 import { Hand } from "../rendererConstants.js";
-import { ISingleVariantMoveInterpreter, LowLevelMovesForAllDancers, MoveInterpreter, PartialLowLevelMove, SemanticPositionsForAllDancers, SingleVariantMoveInterpreter, moveInterpreters } from "./_moveInterpreter.js";
+import { ISingleVariantMoveInterpreter, LowLevelMovesForAllDancers, MoveInterpreter, MoveInterpreterCtorArgs, PartialLowLevelMove, SemanticPositionsForAllDancers, SingleVariantMoveInterpreter, moveInterpreters } from "./_moveInterpreter.js";
 import { dancerIsPair } from "../libfigure/util.js";
 
-const moveName: Move["move"] = "hey";
+const moveName = "hey";
 
-class HeySingleVariant extends SingleVariantMoveInterpreter<Hey, typeof moveName> {
-  moveAsLowLevelMoves(): LowLevelMovesForAllDancers {
-    // Needed for inner functions... that probably should be methods.
-    const move = this.move;
-
-    type HeyStep = {
+type HeyStep = {
   kind: "StandStill" | "Loop" | "CenterPass" | "EndsPassIn" | "EndsPassOut" | "Ricochet",
   endPosition: SemanticPosition,
-    }
+}
 
-    if (this.move.parameters.dir !== "across") {
-      throw new Error("Unsupported hey direction: " + this.move.parameters.dir);
-    }
-
-    let heyParts: number;
-    switch (this.move.parameters.until) {
-      case "half":
-        heyParts = 4;
-        break;
-      case "full":
-        heyParts = 8;
-        break;
-      default:
-        throw new Error("Unsupported hey 'until': " + this.move.parameters.until);
-    }
-    const heyPartBeats: number = this.move.beats / heyParts;
-    // TODO is this right?
-    const firstPassInCenter: boolean = dancerIsPair(this.move.parameters.who);
-    const centerShoulder = firstPassInCenter === this.move.parameters.shoulder ? Hand.Right : Hand.Left;
-    const endsShoulder = centerShoulder.opposite();
-
-    function fixupHeyOtherPath(withoutOtherPath: Map<DancerIdentity, (LowLevelMove & { heyStep?: HeyStep })[]>): Map<DancerIdentity, LowLevelMove[]> {
+function fixupHeyOtherPath(withoutOtherPath: Map<DancerIdentity, (LowLevelMove & { heyStep?: HeyStep })[]>): Map<DancerIdentity, LowLevelMove[]> {
   const numSteps = withoutOtherPath.get(DancerIdentity.OnesLark)!.length;
   for (let i = 0; i < numSteps; i++) {
     for (const id of withoutOtherPath.keys()) {
@@ -105,13 +78,12 @@ class HeySingleVariant extends SingleVariantMoveInterpreter<Hey, typeof moveName
 
   // Object was mutated.
   return withoutOtherPath;
-    }
+}
 
-    return fixupHeyOtherPath(this.handleMove(({ id, startPos }) => {
-      const endsInCircle = startPos.kind === PositionKind.Circle;
-      function heyStepToPartialLowLevelMove(heyStep: HeyStep): PartialLowLevelMove & { heyStep: HeyStep } {
+class HeySingleVariant extends SingleVariantMoveInterpreter<Hey, typeof moveName> {
+  heyStepToPartialLowLevelMove(heyStep: HeyStep): PartialLowLevelMove & { heyStep: HeyStep } {
     return {
-          beats: heyPartBeats,
+      beats: this.moveInterpreter.heyPartBeats,
       // TODO use circle positions on ends? ... unless hey ends in a box the gnat or similar...
       endPosition: heyStep.endPosition,
       movementPattern: heyStep.kind === "StandStill" ? {
@@ -119,7 +91,7 @@ class HeySingleVariant extends SingleVariantMoveInterpreter<Hey, typeof moveName
       } : heyStep.kind === "Loop" ? {
         // TODO Loop should probably be its own kind? Or RotateAround?
         kind: SemanticAnimationKind.Linear,
-            minRotation: endsShoulder === Hand.Right ? +180 : -180,
+        minRotation: this.moveInterpreter.endsShoulder === Hand.Right ? +180 : -180,
       } : heyStep.kind === "Ricochet" ? {
         // TODO This is a hack.
         kind: SemanticAnimationKind.PassBy,
@@ -127,21 +99,24 @@ class HeySingleVariant extends SingleVariantMoveInterpreter<Hey, typeof moveName
         withHands: false,
         otherPath: "Swap",
         facing: "Start",
-            side: endsShoulder,
+        side: this.moveInterpreter.endsShoulder,
       } : {
         kind: SemanticAnimationKind.PassBy,
         around: heyStep.kind === "CenterPass" ? "Center" : heyStep.endPosition.which.leftRightSide(),
         withHands: false,
-            side: heyStep.kind === "CenterPass" ? centerShoulder : endsShoulder,
+        side: heyStep.kind === "CenterPass" ? this.moveInterpreter.centerShoulder : this.moveInterpreter.endsShoulder,
         facing: "Start",
         otherPath: undefined!, // Placeholder, fixup later.
       },
       heyStep,
     };
   }
-      function continueHey(prevStep: HeyStep, stepsLeft: number, beenInCenter: boolean): HeyStep {
+
+  continueHey(prevStep: HeyStep, stepsLeft: number,
+      { beenInCenter, endsInCircle, inCenterFirst }:
+        { beenInCenter: boolean, endsInCircle: boolean, inCenterFirst: boolean }): HeyStep {
     // TODO Not sure why type checker requires rechecking this here.
-        if (move.move !== "hey") throw new Error("Unreachable.");
+    if (this.move.move !== "hey") throw new Error("Unreachable.");
 
     // Continuing hey so everyone is either passing (in center or on ends) or looping on ends.
     if (prevStep.endPosition.kind === PositionKind.Circle) {
@@ -201,19 +176,19 @@ class HeySingleVariant extends SingleVariantMoveInterpreter<Hey, typeof moveName
             ...prevStep.endPosition,
             kind: PositionKind.Circle,
             which: prevStep.endPosition.which.isLeft()
-                  ? (endsShoulder === Hand.Right ? CirclePosition.TopLeft : CirclePosition.BottomLeft)
-                  : (endsShoulder === Hand.Right ? CirclePosition.BottomRight : CirclePosition.TopRight),
+              ? (this.moveInterpreter.endsShoulder === Hand.Right ? CirclePosition.TopLeft : CirclePosition.BottomLeft)
+              : (this.moveInterpreter.endsShoulder === Hand.Right ? CirclePosition.BottomRight : CirclePosition.TopRight),
           },
         }
       }
       else if (!isFacingSide) {
         const rico = inCenterFirst
           ? beenInCenter
-                ? move.parameters.rico3
-                : move.parameters.rico1
+            ? this.move.parameters.rico3
+            : this.move.parameters.rico1
           : beenInCenter
-                ? move.parameters.rico4
-                : move.parameters.rico2;
+            ? this.move.parameters.rico4
+            : this.move.parameters.rico2;
 
         if (rico) {
           const onLeftSide = prevStep.endPosition.which.isLeft();
@@ -224,7 +199,7 @@ class HeySingleVariant extends SingleVariantMoveInterpreter<Hey, typeof moveName
               kind: PositionKind.Circle,
               which: CirclePosition.fromSides(prevStep.endPosition.which.leftRightSide(),
                 // TODO might be swapped
-                    (endsShoulder === Hand.Left) === onLeftSide ? CircleSide.Top : CircleSide.Bottom),
+                (this.moveInterpreter.endsShoulder === Hand.Left) === onLeftSide ? CircleSide.Top : CircleSide.Bottom),
               facing: onLeftSide ? Facing.Left : Facing.Right,
             }
           }
@@ -252,12 +227,16 @@ class HeySingleVariant extends SingleVariantMoveInterpreter<Hey, typeof moveName
     }
   }
 
-      const inCenterFirst = firstPassInCenter && this.findPairOpposite(this.move.parameters.who, id) !== null
-        || this.move.parameters.who2 && this.findPairOpposite(this.move.parameters.who2, id) !== null;
+  moveAsLowLevelMoves(): LowLevelMovesForAllDancers {
+    return fixupHeyOtherPath(this.handleMove(({ id, startPos }) => {
+      const endsInCircle = startPos.kind === PositionKind.Circle;
+
+      const inCenterFirst = this.moveInterpreter.firstPassInCenter && (this.findPairOpposite(this.move.parameters.who, id) !== null)
+        || !!this.move.parameters.who2 && (this.findPairOpposite(this.move.parameters.who2, id) !== null);
 
       let firstHeyStep: HeyStep;
       let startingPos: SemanticPosition;
-      if (firstPassInCenter) {
+      if (this.moveInterpreter.firstPassInCenter) {
         if (startPos.kind !== PositionKind.Circle) {
           throw new Error("Hey starting in center not from circle is unsupported.");
         }
@@ -319,18 +298,60 @@ class HeySingleVariant extends SingleVariantMoveInterpreter<Hey, typeof moveName
 
       const heySteps: HeyStep[] = [firstHeyStep];
       let beenInCenter = firstHeyStep.kind === "CenterPass" || firstHeyStep.kind === "Ricochet";
-      for (let i = 1; i < heyParts; i++) {
-        const isLast = i === heyParts - 1;
-        const nextHeyStep = continueHey(heySteps[i - 1], heyParts - i - 1, beenInCenter);
+      for (let i = 1; i < this.moveInterpreter.heyParts; i++) {
+        const nextHeyStep = this.continueHey(heySteps[i - 1], this.moveInterpreter.heyParts - i - 1, {beenInCenter, endsInCircle, inCenterFirst});
         beenInCenter ||= nextHeyStep.kind === "CenterPass" || nextHeyStep.kind === "Ricochet";
         heySteps.push(nextHeyStep);
       }
-      return this.combine(heySteps.map(heyStepToPartialLowLevelMove), { ...startingPos, hands: undefined });
+      return this.combine(heySteps.map(s => this.heyStepToPartialLowLevelMove(s)), { ...startingPos, hands: undefined });
     }));
   }
 }
 
 class Hey extends MoveInterpreter<typeof moveName> {
+  public readonly heyParts: number;
+  public readonly heyPartBeats: number;
+  public readonly firstPassInCenter: boolean;
+  public readonly centerShoulder: Hand;
+  public readonly endsShoulder: Hand;
+
+  constructor(args: MoveInterpreterCtorArgs<typeof moveName>) {
+    super(args);
+
+    if (this.move.parameters.dir !== "across") {
+      throw new Error("Unsupported hey direction: " + this.move.parameters.dir);
+    }
+
+    if (typeof this.move.parameters.until === "string") {
+      switch (this.move.parameters.until) {
+        case "half":
+          this.heyParts = 4;
+          break;
+        case "full":
+          this.heyParts = 8;
+          break;
+        // TODO Are these right? Can it sometimes be 1 or 3 instead of 2?
+        case "less than half":
+          this.heyParts = 2;
+          break;
+        case "between half and full":
+          this.heyParts = 6;
+        default:
+          throw new Error("Unsupported hey 'until': " + this.move.parameters.until);
+      }
+    }
+    else {
+      // TODO Is this actually this simple?
+      this.heyParts = this.move.parameters.until.time === 1 ? 2 : 6;
+      //throw new Error("Unsupported hey 'until': " + this.move.parameters.until.dancer + " time " + this.move.parameters.until.time);
+    }
+    this.heyPartBeats = this.move.beats / this.heyParts;
+    // TODO is this right?
+    this.firstPassInCenter = dancerIsPair(this.move.parameters.who);
+    this.centerShoulder = this.firstPassInCenter === this.move.parameters.shoulder ? Hand.Right : Hand.Left;
+    this.endsShoulder = this.centerShoulder.opposite();
+  }
+
   buildSingleVariantMoveInterpreter(startingPos: SemanticPositionsForAllDancers): ISingleVariantMoveInterpreter {
     return new HeySingleVariant(this, startingPos);
   }

www/js/moves/madRobin.ts

@@ -1,4 +1,4 @@
-import { SemanticPosition, PositionKind } from "../interpreterCommon.js";
+import { SemanticPosition, PositionKind, DancerDistance } from "../interpreterCommon.js";
 import { Move } from "../libfigureMapper.js";
 import { SemanticAnimationKind } from "../lowLevelMove.js";
 import { ISingleVariantMoveInterpreter, LowLevelMovesForAllDancers, MoveInterpreter, SemanticPositionsForAllDancers, SingleVariantMoveInterpreter, moveInterpreters } from "./_moveInterpreter.js";
@@ -12,6 +12,10 @@ class MadRobinSingleVariant extends SingleVariantMoveInterpreter<MadRobin, typeo
     }
 
     return this.handleCircleMove(({ id, startPos }) => {
+      if (startPos.dancerDistance && startPos.dancerDistance !== DancerDistance.Normal) {
+        throw new Error(this.move.move + " can only start in normal DancerDistance.");
+      }
+
       // Read who of mad robin to decide direction.
       const madRobinClockwise: boolean = (this.findPairOpposite(this.move.parameters.who, id) !== null) === startPos.which.isOnLeftLookingAcross();
 

www/js/moves/pullByDancers.ts

@@ -1,43 +1,71 @@
-import { HandConnection, HandTo, BalanceWeight } from "../interpreterCommon.js";
-import { Move } from "../libfigureMapper.js";
+import { HandConnection, HandTo, BalanceWeight, PositionKind, ShortLinesPosition, SemanticPosition } from "../interpreterCommon.js";
 import { SemanticAnimationKind } from "../lowLevelMove.js";
 import { Hand } from "../rendererConstants.js";
-import { ISingleVariantMoveInterpreter, LowLevelMovesForAllDancers, MoveInterpreter, PartialLowLevelMove, SemanticPositionsForAllDancers, SingleVariantMoveInterpreter, moveInterpreters } from "./_moveInterpreter.js";
+import { ISingleVariantMoveInterpreter, LowLevelMovesForAllDancers, MoveInterpreter, MoveInterpreterCtorArgs, PartialLowLevelMove, SemanticPositionsForAllDancers, SingleVariantMoveInterpreter, Variant, VariantCollection, moveInterpreters } from "./_moveInterpreter.js";
 
-const moveName: Move["move"] = "pull by dancers";
+const moveName = "pull by dancers";
 
 class PullByDancersSingleVariant extends SingleVariantMoveInterpreter<PullByDancers, typeof moveName> {
-  moveAsLowLevelMoves(): LowLevelMovesForAllDancers {
+  moveAsVariants(previousMoveVariant: string): VariantCollection {
+    const res = new Map<string, Variant>();
+
+    for (const toShortLines of [true, false]) {
+      try {
+        res.set(toShortLines ? "ToShortLines" : "FullPullBy", {
+          lowLevelMoves: this.moveAsLowLevelMovesTo(toShortLines),
+          previousMoveVariant
+        });
+      }
+      catch { }
+    }
+
+    return res;
+  }
+
+
+  moveAsLowLevelMovesTo(toShortLines: boolean): LowLevelMovesForAllDancers {
     // TODO Might make sense to think of pull by as not a full swap?
     //  e.g., in Blue and Green Candles, it's treated as only getting to
     //        ShortLinesPosition.Middle* before doing an allemande.
     return this.handlePairedMove(this.move.parameters.who, ({ startPos, around, withPos }) => {
-      const hand = this.move.parameters.hand ? Hand.Right : Hand.Left;
-      const balanceBeats = this.move.parameters.bal
-        ? this.move.beats > 4
-          ? this.move.beats - 4
-          : 2
-        : 0;
-      const balancePartBeats = balanceBeats / 2;
-      const pullBeats = this.move.beats - balanceBeats;
+      if (toShortLines) {
+        if (startPos.kind !== PositionKind.Circle) {
+          throw new Error("ToShortLines variant of " + this.move.move + " only makes sense starting from a circle.");
+        }
+      }
 
       // TODO Adjust facing?
       const startPosition = {
         ...startPos,
         hands: new Map<Hand, HandConnection>([
           [
-            hand,
-            { hand, to: around === "Center" ? HandTo.DiagonalAcrossCircle : HandTo.DancerForward }
-          ]])
+            this.moveInterpreter.hand,
+            { hand: this.moveInterpreter.hand, to: around === "Center" ? HandTo.DiagonalAcrossCircle : HandTo.DancerForward }
+          ]]),
+        facing: startPos.which.facingAcross(),
       };
 
+      const endPos: SemanticPosition = toShortLines
+        ? {
+          ...withPos,
+          hands: undefined,
+          facing: startPosition.facing,
+          kind: PositionKind.ShortLines,
+          which: ShortLinesPosition.fromSide(withPos.which.leftRightSide(), "Middle"),
+          longLines: undefined, // Needed to satisfy type-checker.
+        }
+        : {
+          ...withPos,
+          hands: undefined,
+          facing: startPosition.facing,
+        };
       const passBy: PartialLowLevelMove = {
-        beats: pullBeats,
-        endPosition: { ...withPos, facing: startPos.facing },
+        beats: this.moveInterpreter.pullBeats,
+        endPosition: endPos,
         movementPattern: {
           kind: SemanticAnimationKind.PassBy,
           around,
-          side: hand,
+          side: this.moveInterpreter.hand,
           withHands: true,
           facing: "Start",
           otherPath: "Swap",
@@ -47,7 +75,7 @@ class PullByDancersSingleVariant extends SingleVariantMoveInterpreter<PullByDanc
       if (this.move.parameters.bal) {
         return this.combine([
           {
-            beats: balancePartBeats,
+            beats: this.moveInterpreter.balancePartBeats,
             endPosition: {
               ...startPosition,
               balance: BalanceWeight.Forward,
@@ -57,7 +85,7 @@ class PullByDancersSingleVariant extends SingleVariantMoveInterpreter<PullByDanc
             }
           },
           {
-            beats: balancePartBeats,
+            beats: this.moveInterpreter.balancePartBeats,
             endPosition: {
               ...startPosition,
               balance: BalanceWeight.Backward,
@@ -70,11 +98,45 @@ class PullByDancersSingleVariant extends SingleVariantMoveInterpreter<PullByDanc
       } else {
         return this.combine([passBy], startPosition);
       }
+    }, !toShortLines ? undefined : ({startPos}) => {
+      return this.combine([{
+        beats: this.move.beats,
+        movementPattern: {
+          kind: SemanticAnimationKind.Linear,
+        },
+        endPosition: {
+          ...startPos,
+          kind: PositionKind.ShortLines,
+          which: ShortLinesPosition.fromSide(startPos.which.leftRightSide(), "Far"),
+          facing: startPos.which.facingAcross(),
+          hands: undefined,
+          longLines: undefined,
+        }
+      }], startPos);
     });
   }
 }
 
 class PullByDancers extends MoveInterpreter<typeof moveName> {
+  public readonly hand: Hand;
+  public readonly balancePartBeats: number;
+  public readonly pullBeats: number; 
+
+  constructor(args: MoveInterpreterCtorArgs<typeof moveName>) {
+    super(args);
+
+    this.hand = this.move.parameters.hand ? Hand.Right : Hand.Left;
+    const balanceBeats = this.move.parameters.bal
+      ? this.move.beats > 4
+        ? this.move.beats - 4
+        : this.move.beats > 2
+          ? 2
+          : this.move.beats / 2
+      : 0;
+    this.balancePartBeats = balanceBeats / 2;
+    this.pullBeats = this.move.beats - balanceBeats;
+  }
+
   buildSingleVariantMoveInterpreter(startingPos: SemanticPositionsForAllDancers): ISingleVariantMoveInterpreter {
     return new PullByDancersSingleVariant(this, startingPos);
   }

www/js/moves/rollAway.ts

@@ -9,7 +9,7 @@ const moveName: Move["move"] = "roll away";
 class RollAwaySingleVariant extends SingleVariantMoveInterpreter<RollAway, typeof moveName> {
   moveAsLowLevelMoves(): LowLevelMovesForAllDancers {
     // TODO maybe can roll away in short lines?
-    return this.handleCirclePairedMove(this.move.parameters.who, ({ id, startPos, withPos }) => {
+    return this.handleCirclePairedMove(this.move.parameters.whom, ({ id, startPos, withPos }) => {
       let isRoller: boolean;
       switch (this.move.parameters.who) {
         case "gentlespoons":

www/js/moves/roryOMore.ts

@@ -1,24 +1,14 @@
-import { PositionKind, SemanticPosition, Facing, BalanceWeight, handsInLine } from "../interpreterCommon.js";
-import { Move } from "../libfigureMapper.js";
+import { PositionKind, SemanticPosition, Facing, BalanceWeight, handsInLine, CircleSide, handsInLongLines } from "../interpreterCommon.js";
 import { SemanticAnimationKind } from "../lowLevelMove.js";
 import { Hand } from "../rendererConstants.js";
-import { ISingleVariantMoveInterpreter, LowLevelMovesForAllDancers, MoveInterpreter, PartialLowLevelMove, SemanticPositionsForAllDancers, SingleVariantMoveInterpreter, moveInterpreters } from "./_moveInterpreter.js";
+import { ISingleVariantMoveInterpreter, LowLevelMovesForAllDancers, MoveInterpreter, MoveInterpreterCtorArgs, PartialLowLevelMove, SemanticPositionsForAllDancers, SingleVariantMoveInterpreter, moveInterpreters } from "./_moveInterpreter.js";
 
-const moveName: Move["move"] = "Rory O'More";
+const moveName = "Rory O'More";
 class RoryOMoreSingleVariant extends SingleVariantMoveInterpreter<RoryOMore, typeof moveName> {
   moveAsLowLevelMoves(): LowLevelMovesForAllDancers {
-    if (this.move.parameters.who !== "everyone") {
-      throw new Error(this.move.move + " that doesn't include everyone is unsupported.");
-    }
 
     // TODO Could be in long or short lines.
-    const roryDir = this.move.parameters.slide ? Hand.Left : Hand.Right;
-    const balBeats = this.move.parameters.bal ? this.move.beats / 2 : 0;
-    const balPartBeats = balBeats / 2;
-    const roryBeats = this.move.beats - balBeats;
     return this.handleMove(({ startPos }) => {
-      const isShortLines: boolean = startPos.kind === PositionKind.ShortLines;
-
       const startingPos: SemanticPosition = {
         ...startPos,
         hands: handsInLine({ wavy: true, which: startPos.which, facing: startPos.facing })
@@ -27,38 +17,61 @@ class RoryOMoreSingleVariant extends SingleVariantMoveInterpreter<RoryOMore, typ
       let endPos: SemanticPosition;
       if (startPos.kind === PositionKind.ShortLines) {
         if (startPos.facing !== Facing.Up && startPos.facing !== Facing.Down) {
-          throw new Error("To be in wavy lines, must be facing up or down, not " + startPos.facing);
+          throw new Error("To be in short wavy lines, must be facing up or down, not " + startPos.facing);
+        }
+        const { newPos: endWhich, wrap } = startPos.which.shiftWithWrap(this.moveInterpreter.dir, startPos.facing);
+        const endLineOffset = !wrap
+          ? startPos.lineOffset
+          : (startPos.lineOffset ?? 0) + wrap;
+        if (wrap) {
+          startingPos.hands = handsInLongLines(true)
         }
-        const endWhich = startPos.which.shift(roryDir, startPos.facing);
         endPos = {
           ...startPos,
           which: endWhich,
-          hands: handsInLine({ wavy: true, which: endWhich, facing: startPos.facing })
+          hands: handsInLine({ wavy: true, which: endWhich, facing: startPos.facing }),
+          lineOffset: endLineOffset,
         };
       } else {
-        throw new Error(this.move.move + " is currently only supported in short lines.");
+        if (startPos.facing !== Facing.Left && startPos.facing !== Facing.Right) {
+          throw new Error("To be in long wavy lines, must be facing left or right, not " + startPos.facing);
+        }
+        const endWhich = startPos.which.swapUpAndDown();
+        const sideTowards = (startPos.facing === Facing.Right)
+                            === (this.moveInterpreter.dir === Hand.Left)
+                              ? CircleSide.Bottom
+                              : CircleSide.Top;
+        const endSetOffset = sideTowards === endWhich.topBottomSide()
+          ? startPos.setOffset
+          : (startPos.setOffset ?? 0) + (sideTowards === CircleSide.Bottom ? +1 : -1);
+        endPos = {
+          ...startPos,
+          which: endWhich,
+          hands: handsInLine({ wavy: true, which: endWhich, facing: startPos.facing }),
+          setOffset: endSetOffset,
+        };
       }
 
       const maybeBalance: PartialLowLevelMove[] = (this.move.parameters.bal ? [
         {
-          beats: balPartBeats,
-          endPosition: { ...startingPos, balance: roryDir === Hand.Left ? BalanceWeight.Left : BalanceWeight.Right },
+          beats: this.moveInterpreter.balPartBeats,
+          endPosition: { ...startingPos, balance: this.moveInterpreter.dir === Hand.Left ? BalanceWeight.Left : BalanceWeight.Right },
           movementPattern: { kind: SemanticAnimationKind.Linear },
         },
         {
-          beats: balPartBeats,
-          endPosition: { ...startingPos, balance: roryDir === Hand.Left ? BalanceWeight.Right : BalanceWeight.Left },
+          beats: this.moveInterpreter.balPartBeats,
+          endPosition: { ...startingPos, balance: this.moveInterpreter.dir === Hand.Left ? BalanceWeight.Right : BalanceWeight.Left },
           movementPattern: { kind: SemanticAnimationKind.Linear },
         },
       ] : []);
 
       return this.combine([...maybeBalance,
       {
-        beats: roryBeats,
+        beats: this.moveInterpreter.roryBeats,
         endPosition: endPos,
         movementPattern: {
           kind: SemanticAnimationKind.Linear,
-          minRotation: roryDir === Hand.Right ? +360 : -360,
+          minRotation: this.moveInterpreter.dir === Hand.Right ? +360 : -360,
           handsDuring: "None",
         },
       }
@@ -68,6 +81,23 @@ class RoryOMoreSingleVariant extends SingleVariantMoveInterpreter<RoryOMore, typ
 }
 
 class RoryOMore extends MoveInterpreter<typeof moveName> {
+  public readonly dir: Hand;
+  public readonly balPartBeats: number;
+  public readonly roryBeats: number;
+
+  constructor(args: MoveInterpreterCtorArgs<typeof moveName>) {
+    super(args);
+
+    if (this.move.parameters.who !== "everyone") {
+      throw new Error(this.move.move + " that doesn't include everyone is unsupported.");
+    }
+
+    this.dir = this.move.parameters.slide ? Hand.Left : Hand.Right;
+    const balBeats = this.move.parameters.bal ? this.move.beats / 2 : 0;
+    this.balPartBeats = balBeats / 2;
+    this.roryBeats = this.move.beats - balBeats;
+  }
+
   buildSingleVariantMoveInterpreter(startingPos: SemanticPositionsForAllDancers): ISingleVariantMoveInterpreter {
     return new RoryOMoreSingleVariant(this, startingPos);
   }

www/js/moves/starPromenade.ts

@@ -1,24 +1,17 @@
 import { DancerDistance, handToDancerToSideInCircleFacingAcross } from "../interpreterCommon.js";
-import { Move } from "../libfigureMapper.js";
 import { SemanticAnimationKind } from "../lowLevelMove.js";
 import { Hand } from "../rendererConstants.js";
-import { ISingleVariantMoveInterpreter, LowLevelMovesForAllDancers, MoveInterpreter, SemanticPositionsForAllDancers, SingleVariantMoveInterpreter, moveInterpreters } from "./_moveInterpreter.js";
+import { ISingleVariantMoveInterpreter, LowLevelMovesForAllDancers, MoveInterpreter, MoveInterpreterCtorArgs, SemanticPositionsForAllDancers, SingleVariantMoveInterpreter, moveInterpreters } from "./_moveInterpreter.js";
 
-const moveName: Move["move"] = "star promenade";
+const moveName = "star promenade";
 
 class StarPromenadeSingleVariant extends SingleVariantMoveInterpreter<StarPromenade, typeof moveName> {
   moveAsLowLevelMoves(): LowLevelMovesForAllDancers {
-    const starPromenadeHand = this.move.parameters.hand ? Hand.Right : Hand.Left;
-    const starPromenadeSwap = (this.move.parameters.circling % 360) === 180;
-    if (!starPromenadeSwap && (this.move.parameters.circling % 360 !== 0)) {
-      throw new Error(this.move.move + " circling by not a multiple of 180 degrees is unsupported.");
-    }
-
     // TODO start promenade hands/show dancers close
     return this.handleCircleMove(({ id, startPos }) => {
       const inCenter = this.findPairOpposite(this.move.parameters.who, id) !== null;
       // TODO Actually, does star promenade end facing out and butterfly whirl swaps?
-      const endWhich = starPromenadeSwap ? startPos.which.swapDiagonal() : startPos.which;
+      const endWhich = this.moveInterpreter.swap ? startPos.which.swapDiagonal() : startPos.which;
       const endFacing = endWhich.facingAcross();
       return this.combine([{
         beats: this.move.beats,
@@ -29,11 +22,13 @@ class StarPromenadeSingleVariant extends SingleVariantMoveInterpreter<StarPromen
           dancerDistance: DancerDistance.Compact,
           // TODO Perhaps different hands indication for "scooped"?
           hands: handToDancerToSideInCircleFacingAcross(endWhich),
+          longLines: undefined,
+          balance: undefined,
         },
         movementPattern: {
           kind: SemanticAnimationKind.RotateAround,
           around: "Center",
-          byHand: inCenter ? starPromenadeHand : undefined,
+          byHand: inCenter ? this.moveInterpreter.hand : undefined,
           close: inCenter,
           minAmount: this.move.parameters.hand ? this.move.parameters.circling : -this.move.parameters.circling,
         }
@@ -43,6 +38,23 @@ class StarPromenadeSingleVariant extends SingleVariantMoveInterpreter<StarPromen
 }
 
 class StarPromenade extends MoveInterpreter<typeof moveName> {
+  public readonly hand: Hand;
+  public readonly swap: boolean;
+
+  constructor(args: MoveInterpreterCtorArgs<typeof moveName>) {
+    super(args);
+
+    this.hand = this.move.parameters.hand ? Hand.Right : Hand.Left;
+    this.swap = (this.move.parameters.circling % 360) === 180;
+    if (!this.swap && (this.move.parameters.circling % 360 !== 0)) {
+      throw new Error(this.move.move + " circling by not a multiple of 180 degrees is unsupported.");
+    }
+  }
+
+  override allowStartingLongLines(): boolean {
+    return true;
+  }
+
   buildSingleVariantMoveInterpreter(startingPos: SemanticPositionsForAllDancers): ISingleVariantMoveInterpreter {
     return new StarPromenadeSingleVariant(this, startingPos);
   }

www/js/moves/swing.ts

@@ -1,39 +1,77 @@
 import { CoupleRole, DanceRole } from "../danceCommon.js";
-import { LongLines, CircleSide, SemanticPosition, CirclePosition, Facing, PositionKind, HandConnection, HandTo, ShortLinesPosition, handsInLine, BalanceWeight, DancerDistance } from "../interpreterCommon.js";
-import { Move } from "../libfigureMapper.js";
+import { LongLines, CircleSide, SemanticPosition, CirclePosition, Facing, PositionKind, HandConnection, HandTo, ShortLinesPosition, handsInLine, BalanceWeight, DancerDistance, isFacingUpOrDown, isLeftRightCircleSide } from "../interpreterCommon.js";
 import { SemanticAnimationKind } from "../lowLevelMove.js";
 import { Hand } from "../rendererConstants.js";
-import { ISingleVariantMoveInterpreter, LowLevelMovesForAllDancers, MoveInterpreter, PartialLowLevelMove, SemanticPositionsForAllDancers, SingleVariantMoveInterpreter, moveInterpreters } from "./_moveInterpreter.js";
+import { ISingleVariantMoveInterpreter, LowLevelMovesForAllDancers, MoveInterpreter, MoveInterpreterCtorArgs, PartialLowLevelMove, SemanticPositionsForAllDancers, SingleVariantMoveInterpreter, Variant, VariantCollection, moveInterpreters } from "./_moveInterpreter.js";
 
-const moveName: Move["move"] = "swing";
+const moveName = "swing";
+
+/* Possible swings:
+ *  - default: start on left/right side, end facing across
+ *  - give and take: start in one corner, end facing across
+ *  - contra corners: just one pair, start on top/bottom side, end facing in to new circle
+ *  - to short lines: start on left/right side, end facing up/down in short lines
+ *  - same role: larks/robins go into center, end facing out
+ *  - join short lines: just one pair in center, joins hands in short lines after
+ *  - ... ?
+ */
+interface SwingEnd {
+  facing: "Across" | Facing.Up | Facing.Down,
+  close: boolean,
+}
+function swingEndString(swingEnd: SwingEnd): string {
+  return swingEnd.facing + (swingEnd.close ? "Close" : "");
+}
+const swingEndValues: SwingEnd[] = [
+  { facing: "Across", close: false},
+  { facing: "Across", close: true},
+  { facing: Facing.Up, close: false},
+  { facing: Facing.Up, close: true},
+  { facing: Facing.Down, close: false},
+  { facing: Facing.Down, close: true},
+];
 
 class SwingSingleVariant extends SingleVariantMoveInterpreter<Swing, typeof moveName> {
-  moveAsLowLevelMoves(): LowLevelMovesForAllDancers {
-    // TODO Use variants instead of nextMove
-    const nextMove = this.moveInterpreter.nextMove;
+  moveAsVariants(previousMoveVariant: string): VariantCollection {
+    const res = new Map<string, Variant>();
 
+    for (const swingEnd of swingEndValues) {
+      try {
+        res.set(swingEndString(swingEnd), {
+          lowLevelMoves: this.moveAsLowLevelMovesFacing(swingEnd),
+          previousMoveVariant
+        });
+      }
+      catch { }
+    }
+
+    return res;
+  }
+
+  moveAsLowLevelMovesFacing(swingEnd: SwingEnd): LowLevelMovesForAllDancers {
     return this.handlePairedMove(this.move.parameters.who, ({ id, startPos, around, withId, withPos }) => {
-      // TODO swing can start from non-circle positions.
-      // TODO swing end is only in notes / looking at next move.
+      if (startPos.longLines && startPos.longLines !== LongLines.Near) {
+        throw new Error(this.move.move + " shouldn't start with long lines " + startPos.longLines);
+      }
 
-      // TODO better way to detect swing end?
-      // TODO more structured way to do this than enumerating next moves here?
-      //      maybe instead of nextMove an optional endPosition for fixing up positions?
-      //      ... but then every move would have to handle that...
       const afterTake = startPos.longLines === LongLines.Near || withPos.longLines === LongLines.Near;
-      const toShortLines = nextMove.move === "down the hall" || nextMove.move === "up the hall";
-      const endFacingAcross = (around === CircleSide.Left || around === CircleSide.Right) && !toShortLines;
+
+      if (around === "Center" && swingEnd.facing === "Across") {
+        throw new Error("Cannot end a swing around the center facing across.");
+      }
+
+      const toShortLines = around === "Center" || (isLeftRightCircleSide(around) && isFacingUpOrDown(swingEnd.facing));
 
       const startWhich = startPos.which;
       const startPosition: SemanticPosition = {
         ...startPos,
-        facing: around === CircleSide.Left || CircleSide.Right
+        facing: isLeftRightCircleSide(around)
           ? (startWhich instanceof CirclePosition
             ? afterTake
               ? startPos.longLines === LongLines.Near ? startWhich.facingOut() : startWhich.facingAcross()
-              : (startWhich.topBottomSide() === CircleSide.Bottom ? Facing.Up : Facing.Down)
+              : startWhich.facingUpOrDown()
             : startWhich.facingSide())
-          : (startWhich.isLeft() ? Facing.Right : Facing.Left),
+          : startWhich.facingAcross(),
       };
 
       const swingRole = id.danceRole != withId.setIdentity.danceRole
@@ -47,71 +85,43 @@ class SwingSingleVariant extends SingleVariantMoveInterpreter<Swing, typeof move
               ? (withId.relativeLine > 0 ? DanceRole.Lark : DanceRole.Robin)
               : /* should be unreachable as this means withId is equal to id */ DanceRole.Lark;
 
-      // TODO This assumes swing around right/left, not center or top/bottom.
-      let endPosition: SemanticPosition;
-      if (endFacingAcross) {
-        endPosition = {
-          ...startPos,
-          kind: PositionKind.Circle,
-          which: startWhich instanceof CirclePosition
-            ? (startWhich.isOnLeftLookingAcross() === (swingRole === DanceRole.Lark)
-              ? startWhich
-              : startWhich.swapUpAndDown())
-            : (startWhich.isLeft()
-              ? (swingRole === DanceRole.Lark ? CirclePosition.BottomLeft : CirclePosition.TopLeft)
-              : (swingRole === DanceRole.Lark ? CirclePosition.TopRight : CirclePosition.BottomRight)),
-          facing: startWhich.leftRightSide() === CircleSide.Left ? Facing.Right : Facing.Left,
-          balance: undefined,
-          dancerDistance: undefined,
-          longLines: undefined,
-          hands: new Map<Hand, HandConnection>([swingRole === DanceRole.Lark
+      const endFacing = swingEnd.facing === "Across" ? startWhich.facingAcross() : swingEnd.facing;
+      const endWhich = toShortLines && /*always true, just for type-checker*/isFacingUpOrDown(swingEnd.facing)
+        ? ShortLinesPosition.fromSwing(around, swingRole, swingEnd.facing)
+        : CirclePosition.fromSwing(/*always true, just for type-checker*/<CircleSide>around, swingRole, swingEnd.facing)
+
+      const endHands = toShortLines
+        ? handsInLine({ wavy: false, which: endWhich, facing: endFacing })
+        : new Map<Hand, HandConnection>([swingRole === DanceRole.Lark
             ? [Hand.Right, { to: HandTo.DancerRight, hand: Hand.Left }]
-            : [Hand.Left, { to: HandTo.DancerLeft, hand: Hand.Right }]]),
-        };
-      } else if (toShortLines) {
-        const endFacing = nextMove.move === "down the hall" !== (nextMove.parameters.facing === "backward")
-          ? Facing.Down
-          : Facing.Up;
-        const endWhich = startWhich.isLeft()
-          ? ((endFacing === Facing.Down) === (swingRole === DanceRole.Lark) ? ShortLinesPosition.FarLeft : ShortLinesPosition.MiddleLeft)
-          : ((endFacing === Facing.Down) === (swingRole === DanceRole.Lark) ? ShortLinesPosition.MiddleRight : ShortLinesPosition.FarRight)
-        endPosition = {
+            : [Hand.Left, { to: HandTo.DancerLeft, hand: Hand.Right }]]);
+
+      const partialEndPosition = {
         ...startPos,
-          kind: PositionKind.ShortLines,
-          which: endWhich,
         facing: endFacing,
         balance: undefined,
-          dancerDistance: undefined,
+        dancerDistance: swingEnd.close ? DancerDistance.Compact : undefined,
         longLines: undefined,
-          hands: handsInLine({ wavy: false, which: endWhich, facing: endFacing }),
-        };
+        hands: endHands,
       }
-      else {
-        // TODO Need to figure out the logic of knowing if this should be facing up or down.
-        //  Probably based on knowing Ones vs. Twos? Also then the not-participating-dancers need their
-        //  "standing still" to update that they are in a new set...
-        //throw new Error("Swing to new circle currently unsupported.");
-        endPosition = {
-          // end not facing across or in short lines, so transitioning to new circle like in many contra corners dances.
-          ...startPos,
-        };
+      let endPosition: SemanticPosition = toShortLines ? {
+        ...partialEndPosition,
+        kind: PositionKind.ShortLines,
+        which: <ShortLinesPosition>endWhich,
+      } : {
+        ...partialEndPosition,
+        kind: PositionKind.Circle,
+        which: <CirclePosition>endWhich,
       }
 
-      const swingBeats = this.move.parameters.prefix === "none" ? this.move.beats
-        : this.move.parameters.prefix === "balance"
-          ? this.move.beats > 8 ? 8 : this.move.beats - 4
-          : this.move.parameters.prefix === "meltdown"
-            ? this.move.beats - 4
-            : (() => { throw "Unknown swing prefix: " + this.move.parameters.prefix })();
-
       const swing: PartialLowLevelMove = {
-        beats: swingBeats,
+        beats: this.moveInterpreter.swingBeats,
         endPosition: endPosition,
         movementPattern: {
           kind: SemanticAnimationKind.Swing,
           minAmount: 360,
           around,
-          endFacing: startWhich.leftRightSide() === CircleSide.Left ? Facing.Right : Facing.Left,
+          endFacing,
           swingRole,
           afterTake,
         },
@@ -121,8 +131,6 @@ class SwingSingleVariant extends SingleVariantMoveInterpreter<Swing, typeof move
         case "none":
           return this.combine([swing,], startPosition);
         case "balance":
-          // TODO Right length for balance?
-          const balancePartBeats = this.move.beats > 8 ? (this.move.beats - 8) / 2 : 2;
           const startWithBalHands = {
             ...startPosition,
             hands: new Map<Hand, HandConnection>([
@@ -142,13 +150,13 @@ class SwingSingleVariant extends SingleVariantMoveInterpreter<Swing, typeof move
             };
           return this.combine([
             {
-              beats: balancePartBeats,
+              beats: this.moveInterpreter.balancePartBeats,
               startPosition: startWithBalHands,
               endPosition: balForwardPos,
               movementPattern: { kind: SemanticAnimationKind.Linear, },
             },
             prevEnd => ({
-              beats: balancePartBeats,
+              beats: this.moveInterpreter.balancePartBeats,
               endPosition: {
                 ...prevEnd,
                 balance: BalanceWeight.Backward,
@@ -158,10 +166,9 @@ class SwingSingleVariant extends SingleVariantMoveInterpreter<Swing, typeof move
             swing,
           ], startPosition);
         case "meltdown":
-          const meltdownBeats = 4; // TODO right number here?
           return this.combine([
             prevEnd => ({
-              beats: meltdownBeats,
+              beats: this.moveInterpreter.meltdownBeats,
               endPosition: { ...prevEnd, dancerDistance: DancerDistance.Compact },
               movementPattern: {
                 kind: SemanticAnimationKind.RotateAround,
@@ -179,6 +186,53 @@ class SwingSingleVariant extends SingleVariantMoveInterpreter<Swing, typeof move
 }
 
 class Swing extends MoveInterpreter<typeof moveName> {
+  public readonly swingBeats: number;
+  public readonly balancePartBeats: number;
+  public readonly meltdownBeats: number;
+
+  constructor(args: MoveInterpreterCtorArgs<typeof moveName>) {
+    super(args);
+
+    switch(this.move.parameters.prefix) {
+      case "none":
+        this.balancePartBeats = 0;
+        this.meltdownBeats = 0;
+        this.swingBeats = this.move.beats;
+        break;
+      case "balance":
+        this.meltdownBeats = 0;
+        this.balancePartBeats = this.move.beats > 8
+          ? (this.move.beats - 8) / 2
+          : this.move.beats > 4
+            ? 2
+            : this.move.beats / 4;
+        this.swingBeats = this.move.beats - this.balancePartBeats * 2;
+        break;
+      case "meltdown":
+        this.balancePartBeats = 0;
+        this.meltdownBeats = this.move.beats >= 8 ? 4 : this.move.beats / 2;
+        this.swingBeats = this.move.beats - this.meltdownBeats;
+        break;
+      default:
+        throw new Error ("Unknown swing prefix: " + this.move.parameters.prefix);
+    }
+    this.swingBeats = this.move.parameters.prefix === "none" ? this.move.beats
+      : this.move.parameters.prefix === "balance"
+        ? this.move.beats > 8 ? 8 : this.move.beats - 4
+        : this.move.parameters.prefix === "meltdown"
+          ? this.move.beats - 4
+          : (() => { throw "Unknown swing prefix: " + this.move.parameters.prefix })();
+  }
+
+  override allowStartingClose(): boolean {
+    return true;
+  }
+
+  override allowStartingLongLines(): boolean {
+    // Long lines is used for LongLines.Near after give and take.
+    return true;
+  }
+
   buildSingleVariantMoveInterpreter(startingPos: SemanticPositionsForAllDancers): ISingleVariantMoveInterpreter {
     return new SwingSingleVariant(this, startingPos);
   }

www/js/renderer.ts

@@ -52,6 +52,8 @@ export class Renderer {
   animation?: Animation;
   extraSets?: number;
   extraLines?: number;
+  trailIncrements: number = 6;
+  trailLengthInBeats: number = 1;
   drawDebug: boolean = false;
 
   constructor(canvas: HTMLCanvasElement, ctx: CanvasRenderingContext2D) {
@@ -170,16 +172,15 @@ export class Renderer {
     if (!this.animation) throw new Error("Attempted to render before setting animation.");
 
     this.clear();
-    const increments = 7;
-    const trailLengthInBeats = 1;
-    const incrementLength = trailLengthInBeats / increments;
+    const increments = this.trailLengthInBeats > 0 && this.trailIncrements > 0 ? this.trailIncrements : 0;
+    const incrementLength = this.trailLengthInBeats / (increments + 1);
     progression ??= 0;
     const offsetSets = this.animation.progression.y === 0
       ? 0
       : -((progression - (progression % 2)) / 2) / ((this.animation.progression.y * 2) / setDistance);
     for (var i = increments; i >= 0; i--) {
-      const beatToDraw = beat - i*incrementLength;
-      this.ctx.globalAlpha = i == 0 ? 1 : (1 - i/increments)*0.3;
+      const beatToDraw = i == 0 ? beat : beat - i*incrementLength;
+      this.ctx.globalAlpha = i == 0 ? 1 : (1 - i / (increments + 1)) * 0.3;
       const positions = this.animation.positionsAtBeat(beatToDraw, progression % 2);
       if (this.drawDebug) this.drawSets(positions, offsetSets, true, true);
       this.drawSets(positions, offsetSets, i === 0, false);