Fix cursor decoding in some special cases

Signed-off-by: Hans Kokx <hans.d.kokx@gmail.com>

lib/src/cursor_handler.dart

@@ -260,6 +260,11 @@ void _startAnimation(String name, bool rtl) {
   _animationTimer?.cancel();
   final registration = _animated[name];
   if (registration == null) return;
+  registration.index = 0;
+  // Show the first frame immediately; a held frame (e.g. a long first delay)
+  // should still be visible the moment the cursor is activated.
+  final suffix = rtl ? _rtlSuffix : "";
+  unawaited(setCursor("$name#0$suffix"));
   _scheduleFrame(name, rtl);
 }
 

lib/src/decoders/ani_decoder.dart

@@ -10,8 +10,9 @@ import "cur_decoder.dart";
 /// Decodes Windows animated cursor (`.ani`) resources.
 ///
 /// An `.ani` file is a RIFF `ACON` container holding an `anih` header, a
-/// `LIST fram` of `icon` subchunks (each a single-frame `.cur`), and an
-/// optional `seq ` chunk that plays frames out of order. This decoder reads
+/// `LIST fram` of `icon` subchunks (each a single-frame `.cur`), an optional
+/// `seq ` chunk that plays frames out of order, and an optional `rate` chunk
+/// giving each play step's duration in 1/60ths of a second. This decoder reads
 /// those structures and produces an [AnimatedCursor].
 class AniDecoder {
   AniDecoder._();
@@ -28,7 +29,8 @@ class AniDecoder {
     // Walk the top-level RIFF chunks.
     var baseDelayMicros = 16 * 1000;
     final frames = <Cursor>[];
-    List<(int, int)>? seq;
+    List<int>? seq;
+    List<int>? rates;
     for (var offset = 12; offset + 8 <= bytes.length;) {
       final id = _fourCc(view, offset);
       final size = view.getUint32(offset + 4, Endian.little);
@@ -49,15 +51,18 @@ class AniDecoder {
           frames.addAll(await _parseFrames(view, body + 4, body + size));
         }
       } else if (id == "seq ") {
-        // The seq chunk is a list of (frameIndex, delay) pairs; the delay is
-        // a per-step rate in 1/60ths of a second (0 meaning "use iDispRate").
-        final pairCount = size ~/ 4;
+        // The seq chunk is an array of frame indices into the fram LIST,
+        // defining the playback order (frames may repeat).
         seq = [
-          for (var i = 0; i < pairCount; i++)
-            (
-              view.getUint16(body + i * 4, Endian.little),
-              view.getUint16(body + i * 4 + 2, Endian.little),
-            ),
+          for (var i = 0; i < size ~/ 4; i++)
+            view.getUint32(body + i * 4, Endian.little),
+        ];
+      } else if (id == "rate") {
+        // The rate chunk arrays a display rate in 1/60ths of a second for each
+        // step of the seq chunk (or each frame in index order when absent).
+        rates = [
+          for (var i = 0; i < size ~/ 4; i++)
+            view.getUint32(body + i * 4, Endian.little),
         ];
       }
 
@@ -67,20 +72,16 @@ class AniDecoder {
 
     if (frames.isEmpty) throw const FormatException("ani has no frames");
 
+    final play = seq ?? List<int>.generate(frames.length, (i) => i);
     final ordered = <Cursor>[];
     final delays = <Duration>[];
-    if (seq != null) {
-      for (final (index, delay) in seq) {
-        if (index < 0 || index >= frames.length) continue;
-        ordered.add(frames[index]);
-        final micros = delay > 0 ? delay * 16666 : baseDelayMicros;
-        delays.add(Duration(microseconds: micros));
-      }
-    } else {
-      ordered.addAll(frames);
-      for (var i = 0; i < frames.length; i++) {
-        delays.add(Duration(microseconds: baseDelayMicros));
-      }
+    for (var i = 0; i < play.length; i++) {
+      final index = play[i];
+      if (index < 0 || index >= frames.length) continue;
+      ordered.add(frames[index]);
+      final rate = rates != null && i < rates.length ? rates[i] : 0;
+      final micros = rate > 0 ? rate * 16666 : baseDelayMicros;
+      delays.add(Duration(microseconds: micros));
     }
     if (ordered.isEmpty)
       throw const FormatException("ani has no playable frames");
@@ -89,6 +90,11 @@ class AniDecoder {
   }
 
   /// Decodes [bytes] into an animated cursor, scaling frames per [options].
+  ///
+  /// A `seq ` chunk may reference the same frame (and so the same
+  /// [Cursor.image]) multiple times in different play steps. Scaling reuses
+  /// the result for each duplicate so the shared source image is consumed
+  /// exactly once.
   static Future<AnimatedCursor> decodeWithOptions(
     Uint8List bytes,
     DecodeOptions options,
@@ -97,31 +103,42 @@ class AniDecoder {
     final target = options.targetSize;
     if (target == null && options.systemScale == 1.0) return animated;
 
+    final cache = <Cursor, Future<Cursor>>{};
     final frames = <Cursor>[];
     for (final cursor in animated.frames) {
-      if (target != null) {
-        frames.add(
-          await CursorScaler.scaleTo(
-            cursor.image,
-            cursor.hotspotX,
-            cursor.hotspotY,
-            target,
-          ),
-        );
-      } else {
-        frames.add(
-          await CursorScaler.scaleTo(
-            cursor.image,
-            cursor.hotspotX,
-            cursor.hotspotY,
-            cursor.image.width * options.systemScale,
-          ),
-        );
+      final cached = cache[cursor];
+      if (cached != null) {
+        frames.add(await cached);
+        continue;
       }
+      final scaled = _scaleFrame(cursor, target, options.systemScale);
+      cache[cursor] = scaled;
+      frames.add(await scaled);
     }
     return AnimatedCursor(frames: frames, frameDelays: animated.frameDelays);
   }
 
+  static Future<Cursor> _scaleFrame(
+    Cursor cursor,
+    double? target,
+    double systemScale,
+  ) async {
+    if (target != null) {
+      return CursorScaler.scaleTo(
+        cursor.image,
+        cursor.hotspotX,
+        cursor.hotspotY,
+        target,
+      );
+    }
+    return CursorScaler.scaleTo(
+      cursor.image,
+      cursor.hotspotX,
+      cursor.hotspotY,
+      cursor.image.width * systemScale,
+    );
+  }
+
   /// Parses consecutive `icon` subchunks starting at [start] (inclusive) up to
   /// [end] (exclusive) within the `LIST fram` body.
   static Future<List<Cursor>> _parseFrames(

lib/src/decoders/cur_decoder.dart

@@ -71,6 +71,23 @@ class CurDecoder {
       throw const FormatException("cursor bitmap data truncated");
     }
 
+    final data = Uint8List.sublistView(bytes, offset, offset + size);
+    // Modern cursors may embed a full PNG (or other compressed image) instead
+    // of a raw DIB bitmap. Detect it and hand it to the image codec directly.
+    if (data.length >= 8 &&
+        data[0] == 0x89 && // PNG magic
+        data[1] == 0x50 && // 'P'
+        data[2] == 0x4e && // 'N'
+        data[3] == 0x47) {
+      // 'G'
+      final image = await _decodeCompressed(data);
+      return Cursor(
+        image: image,
+        hotspotX: hotspotX.clamp(0, image.width - 1),
+        hotspotY: hotspotY.clamp(0, image.height - 1),
+      );
+    }
+
     final dib = ByteData.sublistView(bytes, offset, offset + size);
     if (dib.lengthInBytes < 40) {
       throw const FormatException("cursor DIB data too small");
@@ -208,4 +225,18 @@ class CurDecoder {
     );
     return completer.future;
   }
+
+  static Future<ui.Image> _decodeCompressed(Uint8List bytes) async {
+    try {
+      final codec = await ui.instantiateImageCodec(bytes);
+      try {
+        final frame = await codec.getNextFrame();
+        return frame.image;
+      } finally {
+        codec.dispose();
+      }
+    } on Exception {
+      throw const FormatException("unsupported compressed cursor data");
+    }
+  }
 }