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Merged
veloce merged 3 commits into from
Feb 13, 2026
Merged

feat: teach Chessboard to support DropMoves #84

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36dc899
feat: teach Chessboard to support DropMoves
tom-anders Feb 3, 2026
e049c09
fix: don't call onMove for invalid DropMoves
tom-anders Feb 4, 2026
1c15643
add test to verify that pawns cannot be dropped on backrank
tom-anders Feb 4, 2026
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181 changes: 142 additions & 39 deletions example/lib/main.dart
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Original file line number Diff line number Diff line change
Expand Up @@ -75,9 +75,9 @@ class _HomePageState extends State<HomePage> {
Position position = Chess.initial;
Side orientation = Side.white;
String fen = kInitialBoardFEN;
NormalMove? lastMove;
Move? lastMove;
NormalMove? promotionMove;
NormalMove? premove;
Move? premove;
ValidMoves validMoves = IMap(const {});
Side sideToMove = Side.white;
PieceSet pieceSet = PieceSet.gioco;
Expand All @@ -87,19 +87,31 @@ class _HomePageState extends State<HomePage> {
bool drawMode = true;
bool pieceAnimation = true;
bool dragMagnify = true;
bool testDropMoves = false;
Mode playMode = Mode.botPlay;
Position? lastPos;
ISet<Shape> shapes = ISet();
bool showBorder = false;

Position get initialPosition => testDropMoves
? Crazyhouse.initial.copyWith(
// Fill initial pockets for easier testing
pockets: Pockets.empty
.increment(Side.white, Role.pawn)
.increment(Side.white, Role.knight)
.increment(Side.white, Role.bishop)
.increment(Side.white, Role.rook)
.increment(Side.white, Role.queen))
: Chess.initial;

@override
Widget build(BuildContext context) {
Widget _buildNewRoundButton() => FilledButton.icon(
icon: const Icon(Icons.refresh_rounded),
label: const Text('New Round'),
onPressed: () {
setState(() {
position = Chess.initial;
position = initialPosition;
fen = position.fen;
validMoves = makeLegalMoves(position);
lastMove = null;
Expand Down Expand Up @@ -280,6 +292,15 @@ class _HomePageState extends State<HomePage> {
},
),
),
_buildSettingsButton(
label: 'Test Drop Moves',
value: testDropMoves ? 'ON' : 'OFF',
onPressed: () {
setState(() {
testDropMoves = !testDropMoves;
position = initialPosition;
});
}),
],
),
],
Expand All @@ -299,41 +320,42 @@ class _HomePageState extends State<HomePage> {
},
);

final settings = ChessboardSettings(
pieceAssets: pieceSet.assets,
colorScheme: boardTheme.colors,
border: showBorder
? BoardBorder(
width: 16.0,
color: _darken(boardTheme.colors.darkSquare, 0.2),
)
: null,
enableCoordinates: true,
animationDuration:
pieceAnimation ? const Duration(milliseconds: 200) : Duration.zero,
dragFeedbackScale: dragMagnify ? 2.0 : 1.0,
dragTargetKind: dragTargetKind,
drawShape: DrawShapeOptions(
enable: drawMode,
onCompleteShape: _onCompleteShape,
onClearShapes: () {
setState(() {
shapes = ISet();
});
},
),
pieceShiftMethod: pieceShiftMethod,
autoQueenPromotionOnPremove: false,
pieceOrientationBehavior: playMode == Mode.freePlay
? PieceOrientationBehavior.opponentUpsideDown
: PieceOrientationBehavior.facingUser,
enableDropMoves: testDropMoves,
);
Widget _buildChessBoardWidget() => Center(
child: LayoutBuilder(
builder: (context, constraints) {
return Chessboard(
final chessboard = Chessboard(
size: min(constraints.maxWidth, constraints.maxHeight),
settings: ChessboardSettings(
pieceAssets: pieceSet.assets,
colorScheme: boardTheme.colors,
border: showBorder
? BoardBorder(
width: 16.0,
color: _darken(boardTheme.colors.darkSquare, 0.2),
)
: null,
enableCoordinates: true,
animationDuration: pieceAnimation
? const Duration(milliseconds: 200)
: Duration.zero,
dragFeedbackScale: dragMagnify ? 2.0 : 1.0,
dragTargetKind: dragTargetKind,
drawShape: DrawShapeOptions(
enable: drawMode,
onCompleteShape: _onCompleteShape,
onClearShapes: () {
setState(() {
shapes = ISet();
});
},
),
pieceShiftMethod: pieceShiftMethod,
autoQueenPromotionOnPremove: false,
pieceOrientationBehavior: playMode == Mode.freePlay
? PieceOrientationBehavior.opponentUpsideDown
: PieceOrientationBehavior.facingUser,
),
settings: settings,
orientation: orientation,
fen: fen,
lastMove: lastMove,
Expand All @@ -360,6 +382,29 @@ class _HomePageState extends State<HomePage> {
),
shapes: shapes.isNotEmpty ? shapes : null,
);

return Column(
crossAxisAlignment: CrossAxisAlignment.stretch,
children: [
if (testDropMoves)
CrazyhouseMenu(
position: position,
side: Side.black,
pieceSet: pieceSet,
squareSize: chessboard.squareSize,
settings: settings,
),
chessboard,
if (testDropMoves)
CrazyhouseMenu(
position: position,
side: Side.white,
pieceSet: pieceSet,
squareSize: chessboard.squareSize,
settings: settings,
),
],
);
},
),
);
Expand Down Expand Up @@ -564,7 +609,7 @@ class _HomePageState extends State<HomePage> {
super.initState();
}

void _onSetPremove(NormalMove? move) {
void _onSetPremove(Move? move) {
setState(() {
premove = move;
});
Expand All @@ -588,9 +633,9 @@ class _HomePageState extends State<HomePage> {
});
}

void _playMove(NormalMove move, {bool? isDrop, bool? isPremove}) {
void _playMove(Move move, {bool? isDrop, bool? isPremove}) {
lastPos = position;
if (isPromotionPawnMove(move)) {
if (move is NormalMove && isPromotionPawnMove(move)) {
setState(() {
promotionMove = move;
});
Expand All @@ -608,9 +653,9 @@ class _HomePageState extends State<HomePage> {
}
}

void _onUserMoveAgainstBot(NormalMove move, {isDrop}) async {
void _onUserMoveAgainstBot(Move move, {isDrop}) async {
lastPos = position;
if (isPromotionPawnMove(move)) {
if (move is NormalMove && isPromotionPawnMove(move)) {
setState(() {
promotionMove = move;
});
Expand Down Expand Up @@ -673,3 +718,61 @@ Color _darken(Color c, [double amount = .1]) {
assert(amount >= 0 && amount <= 1);
return Color.lerp(c, const Color(0xFF000000), amount) ?? c;
}

class CrazyhouseMenu extends StatelessWidget {
const CrazyhouseMenu({
super.key,
required this.side,
required this.pieceSet,
required this.squareSize,
required this.settings,
required this.position,
});

final Side side;
final PieceSet pieceSet;
final double squareSize;
final Position position;

final ChessboardSettings settings;

@override
Widget build(BuildContext context) {
return Container(
color: Colors.grey,
child: Row(
mainAxisSize: MainAxisSize.min,
mainAxisAlignment: MainAxisAlignment.center,
children: Role.values.where((role) => role != Role.king).map(
(role) {
final piece = Piece(role: role, color: side);

final hasPieceInPocket =
(position.pockets?.of(side, role) ?? 0) > 0;

return IgnorePointer(
ignoring: !hasPieceInPocket,
child: Draggable(
data: piece,
feedback: PieceDragFeedback(
scale: settings.dragFeedbackScale,
squareSize: squareSize,
piece: piece,
pieceAssets: pieceSet.assets,
),
child: PieceWidget(
piece: piece,
size: squareSize,
pieceAssets: pieceSet.assets,
opacity: hasPieceInPocket
? null
: const AlwaysStoppedAnimation(0.3),
),
),
);
},
).toList(),
),
);
}
}
10 changes: 9 additions & 1 deletion lib/src/board_settings.dart
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Original file line number Diff line number Diff line change
Expand Up @@ -106,6 +106,7 @@ class ChessboardSettings {
this.autoQueenPromotion = false,
this.autoQueenPromotionOnPremove = true,
this.pieceShiftMethod = PieceShiftMethod.either,
this.enableDropMoves = false,
});

/// Theme of the board
Expand Down Expand Up @@ -175,6 +176,9 @@ class ChessboardSettings {
/// Controls how moves are made.
final PieceShiftMethod pieceShiftMethod;

/// Whether dragging a [Draggable<Piece>] onto the board triggers a [DropMove].
final bool enableDropMoves;

/// Shape drawing options object containing data about how new shapes can be drawn.
final DrawShapeOptions drawShape;

Expand Down Expand Up @@ -205,7 +209,8 @@ class ChessboardSettings {
other.autoQueenPromotion == autoQueenPromotion &&
other.autoQueenPromotionOnPremove == autoQueenPromotionOnPremove &&
other.pieceShiftMethod == pieceShiftMethod &&
other.drawShape == drawShape;
other.drawShape == drawShape &&
other.enableDropMoves == enableDropMoves;
}

@override
Expand All @@ -229,6 +234,7 @@ class ChessboardSettings {
autoQueenPromotionOnPremove,
pieceShiftMethod,
drawShape,
enableDropMoves,
);

ChessboardSettings copyWith({
Expand All @@ -252,6 +258,7 @@ class ChessboardSettings {
bool? autoQueenPromotionOnPremove,
PieceShiftMethod? pieceShiftMethod,
DrawShapeOptions? drawShape,
bool? enableDropMoves,
}) {
return ChessboardSettings(
colorScheme: colorScheme ?? this.colorScheme,
Expand All @@ -278,6 +285,7 @@ class ChessboardSettings {
autoQueenPromotion: autoQueenPromotion ?? this.autoQueenPromotion,
pieceShiftMethod: pieceShiftMethod ?? this.pieceShiftMethod,
drawShape: drawShape ?? this.drawShape,
enableDropMoves: enableDropMoves ?? this.enableDropMoves,
);
}
}
6 changes: 3 additions & 3 deletions lib/src/models.dart
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Original file line number Diff line number Diff line change
Expand Up @@ -56,7 +56,7 @@ class GameData {
/// Callback called after a move has been made.
///
/// If the move has been made with drag and drop, `isDrop` will be true.
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Copilot AI Feb 4, 2026

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The documentation comment states "If the move has been made with drag and drop, isDrop will be true." However, this is now ambiguous. The isDrop parameter could mean either:

  1. A drag-and-drop interaction (vs tap-to-select)
  2. A DropMove (vs NormalMove)

Consider updating the documentation to clarify this distinction, especially since the code at line 420 in board.dart sets isDrop: true specifically for DropMoves (pieces dragged from outside the board), not for all drag-and-drop moves.

Suggested change
/// If the move has been made with drag and drop, `isDrop` will be true.
/// The optional [isDrop] flag is `true` when the move is a drop move,
/// i.e. a piece is placed onto the board from outside (as opposed to a
/// normal move of a piece already on the board). It does not indicate
/// whether the user interaction was performed via drag-and-drop or
/// tap-to-select.

Copilot uses AI. Check for mistakes.
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@tom-anders tom-anders Feb 4, 2026

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@veloce I also thought about this, do we want to rename to viaDragAndDrop maybe?

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@veloce veloce Feb 5, 2026

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I think this is not even used by the app... But we should leave it in case other folks use it. In any case it is BC so major version.

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@veloce veloce Feb 5, 2026

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IIRC I added that because the old app was using this metadata to send to server (don't remember why).

final void Function(NormalMove, {bool? isDrop}) onMove;
final void Function(Move, {bool? isDrop}) onMove;

/// Callback called after a piece has been selected for promotion.
///
Expand All @@ -77,12 +77,12 @@ typedef Premovable =
/// Will be shown on the board as a preview move.
///
/// Chessground will not play the premove automatically, it is up to the library user to play it.
NormalMove? premove,
Move? premove,

/// Callback called after a premove has been set/unset.
///
/// If `null`, the premove will be unset.
void Function(NormalMove?) onSetPremove,
void Function(Move?) onSetPremove,
});

/// Describes a set of piece assets.
Expand Down
4 changes: 2 additions & 2 deletions lib/src/widgets/animation.dart
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Original file line number Diff line number Diff line change
Expand Up @@ -17,15 +17,15 @@ typedef FadingPieces = Map<Square, Piece>;
(TranslatingPieces, FadingPieces) preparePieceAnimations(
Pieces oldPosition,
Pieces newPosition, {
NormalMove? lastDrop,
Move? lastDrop,
}) {
final Map<Square, ({Piece piece, Square from})> translatingPieces = {};
final Map<Square, Piece> fadingPieces = {};
final List<(Piece, Square)> newOnSquare = [];
final List<(Piece, Square)> missingOnSquare = [];
final Set<Square> animatedOrigins = {};
for (final s in Square.values) {
if (s == lastDrop?.from || s == lastDrop?.to) {
if ((lastDrop is NormalMove && s == lastDrop.from) || s == lastDrop?.to) {
continue;
}
final oldP = oldPosition[s];
Expand Down
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