[skwasm] use temporary RawPaint objects (attempt #2) (#55035)

Relands #54917. The change is the same as before, except now the native resources for `SkwasmColorFilter` and `SkwasmImageFilter` classes are no longer GC'd. Instead, we use manually managed native handles (vended and scoped by `withRawColorFilter` and `withRawImageFilter`). The bug in the previous PR was that filter objects were disposed with the paint while the framework continued holding onto them. When GC kicked the finalization registry, it attempted to double-free the filters.

Author: yjbanov

lib/web_ui/lib/src/engine/skwasm/skwasm_impl/canvas.dart

@@ -29,27 +29,33 @@ class SkwasmCanvas implements SceneCanvas {
 
   @override
   void saveLayer(ui.Rect? bounds, ui.Paint paint) {
-    paint as SkwasmPaint;
+    final paintHandle = (paint as SkwasmPaint).toRawPaint();
     if (bounds != null) {
       withStackScope((StackScope s) {
-        canvasSaveLayer(_handle, s.convertRectToNative(bounds), paint.handle, nullptr);
+        canvasSaveLayer(_handle, s.convertRectToNative(bounds), paintHandle, nullptr);
       });
     } else {
-      canvasSaveLayer(_handle, nullptr, paint.handle, nullptr);
+      canvasSaveLayer(_handle, nullptr, paintHandle, nullptr);
     }
+    paintDispose(paintHandle);
   }
 
   @override
   void saveLayerWithFilter(ui.Rect? bounds, ui.Paint paint, ui.ImageFilter imageFilter) {
     final SkwasmImageFilter nativeFilter = SkwasmImageFilter.fromUiFilter(imageFilter);
-    paint as SkwasmPaint;
+    final paintHandle = (paint as SkwasmPaint).toRawPaint();
     if (bounds != null) {
       withStackScope((StackScope s) {
-        canvasSaveLayer(_handle, s.convertRectToNative(bounds), paint.handle, nativeFilter.handle);
+        nativeFilter.withRawImageFilter((nativeFilterHandle) {
+          canvasSaveLayer(_handle, s.convertRectToNative(bounds), paintHandle, nativeFilterHandle);
+        });
       });
     } else {
-      canvasSaveLayer(_handle, nullptr, paint.handle, nativeFilter.handle);
+      nativeFilter.withRawImageFilter((nativeFilterHandle) {
+        canvasSaveLayer(_handle, nullptr, paintHandle, nativeFilterHandle);
+      });
     }
+    paintDispose(paintHandle);
   }
 
   @override
@@ -111,136 +117,158 @@ class SkwasmCanvas implements SceneCanvas {
 
   @override
   void drawLine(ui.Offset p1, ui.Offset p2, ui.Paint paint) {
-    paint as SkwasmPaint;
-    canvasDrawLine(_handle, p1.dx, p1.dy, p2.dx, p2.dy, paint.handle);
+    final paintHandle = (paint as SkwasmPaint).toRawPaint();
+    canvasDrawLine(_handle, p1.dx, p1.dy, p2.dx, p2.dy, paintHandle);
+    paintDispose(paintHandle);
   }
 
   @override
   void drawPaint(ui.Paint paint) {
-    paint as SkwasmPaint;
-    canvasDrawPaint(_handle, paint.handle);
+    final paintHandle = (paint as SkwasmPaint).toRawPaint();
+    canvasDrawPaint(_handle, paintHandle);
+    paintDispose(paintHandle);
   }
 
   @override
   void drawRect(ui.Rect rect, ui.Paint paint) {
-    paint as SkwasmPaint;
+    final paintHandle = (paint as SkwasmPaint).toRawPaint();
     withStackScope((StackScope s) {
       canvasDrawRect(
         _handle,
         s.convertRectToNative(rect),
-        paint.handle
+        paintHandle
       );
     });
+    paintDispose(paintHandle);
   }
 
   @override
   void drawRRect(ui.RRect rrect, ui.Paint paint) {
-    paint as SkwasmPaint;
+    final paintHandle = (paint as SkwasmPaint).toRawPaint();
     withStackScope((StackScope s) {
       canvasDrawRRect(
         _handle,
         s.convertRRectToNative(rrect),
-        paint.handle
+        paintHandle
       );
     });
+    paintDispose(paintHandle);
   }
 
   @override
   void drawDRRect(ui.RRect outer, ui.RRect inner, ui.Paint paint) {
-    paint as SkwasmPaint;
+    final paintHandle = (paint as SkwasmPaint).toRawPaint();
     withStackScope((StackScope s) {
       canvasDrawDRRect(
         _handle,
         s.convertRRectToNative(outer),
         s.convertRRectToNative(inner),
-        paint.handle
+        paintHandle
       );
     });
+    paintDispose(paintHandle);
   }
 
   @override
   void drawOval(ui.Rect rect, ui.Paint paint) {
-    paint as SkwasmPaint;
+    final paintHandle = (paint as SkwasmPaint).toRawPaint();
     withStackScope((StackScope s) {
-      canvasDrawOval(_handle, s.convertRectToNative(rect), paint.handle);
+      canvasDrawOval(_handle, s.convertRectToNative(rect), paintHandle);
     });
+    paintDispose(paintHandle);
   }
 
   @override
   void drawCircle(ui.Offset center, double radius, ui.Paint paint) {
-    paint as SkwasmPaint;
-    canvasDrawCircle(_handle, center.dx, center.dy, radius, paint.handle);
+    final paintHandle = (paint as SkwasmPaint).toRawPaint();
+    canvasDrawCircle(_handle, center.dx, center.dy, radius, paintHandle);
+    paintDispose(paintHandle);
   }
 
   @override
   void drawArc(ui.Rect rect, double startAngle, double sweepAngle,
       bool useCenter, ui.Paint paint) {
-    paint as SkwasmPaint;
+    final paintHandle = (paint as SkwasmPaint).toRawPaint();
     withStackScope((StackScope s) {
       canvasDrawArc(
         _handle,
         s.convertRectToNative(rect),
         ui.toDegrees(startAngle),
         ui.toDegrees(sweepAngle),
         useCenter,
-        paint.handle
+        paintHandle,
       );
     });
+    paintDispose(paintHandle);
   }
 
   @override
   void drawPath(ui.Path path, ui.Paint paint) {
-    paint as SkwasmPaint;
     path as SkwasmPath;
-    canvasDrawPath(_handle, path.handle, paint.handle);
+    final paintHandle = (paint as SkwasmPaint).toRawPaint();
+    canvasDrawPath(_handle, path.handle, paintHandle);
+    paintDispose(paintHandle);
   }
 
   @override
-  void drawImage(ui.Image image, ui.Offset offset, ui.Paint paint) =>
+  void drawImage(ui.Image image, ui.Offset offset, ui.Paint paint) {
+    final paintHandle = (paint as SkwasmPaint).toRawPaint();
     canvasDrawImage(
       _handle,
       (image as SkwasmImage).handle,
       offset.dx,
       offset.dy,
-      (paint as SkwasmPaint).handle,
+      paintHandle,
       paint.filterQuality.index,
     );
+    paintDispose(paintHandle);
+  }
 
   @override
   void drawImageRect(
     ui.Image image,
     ui.Rect src,
     ui.Rect dst,
-    ui.Paint paint) => withStackScope((StackScope scope) {
-    final Pointer<Float> sourceRect = scope.convertRectToNative(src);
-    final Pointer<Float> destRect = scope.convertRectToNative(dst);
-    canvasDrawImageRect(
-      _handle,
-      (image as SkwasmImage).handle,
-      sourceRect,
-      destRect,
-      (paint as SkwasmPaint).handle,
-      paint.filterQuality.index,
-    );
-  });
+    ui.Paint paint,
+  ) {
+    withStackScope((StackScope scope) {
+      final Pointer<Float> sourceRect = scope.convertRectToNative(src);
+      final Pointer<Float> destRect = scope.convertRectToNative(dst);
+      final paintHandle = (paint as SkwasmPaint).toRawPaint();
+      canvasDrawImageRect(
+        _handle,
+        (image as SkwasmImage).handle,
+        sourceRect,
+        destRect,
+        paintHandle,
+        paint.filterQuality.index,
+      );
+      paintDispose(paintHandle);
+    });
+  }
 
   @override
   void drawImageNine(
     ui.Image image,
     ui.Rect center,
     ui.Rect dst,
-    ui.Paint paint) => withStackScope((StackScope scope) {
-    final Pointer<Int32> centerRect = scope.convertIRectToNative(center);
-    final Pointer<Float> destRect = scope.convertRectToNative(dst);
-    canvasDrawImageNine(
-      _handle,
-      (image as SkwasmImage).handle,
-      centerRect,
-      destRect,
-      (paint as SkwasmPaint).handle,
-      paint.filterQuality.index,
-    );
-  });
+    ui.Paint paint,
+  ) {
+    withStackScope((StackScope scope) {
+      final Pointer<Int32> centerRect = scope.convertIRectToNative(center);
+      final Pointer<Float> destRect = scope.convertRectToNative(dst);
+      final paintHandle = (paint as SkwasmPaint).toRawPaint();
+      canvasDrawImageNine(
+        _handle,
+        (image as SkwasmImage).handle,
+        centerRect,
+        destRect,
+        paintHandle,
+        paint.filterQuality.index,
+      );
+      paintDispose(paintHandle);
+    });
+  }
 
   @override
   void drawPicture(ui.Picture picture) {
@@ -264,13 +292,15 @@ class SkwasmCanvas implements SceneCanvas {
     ui.Paint paint
   ) => withStackScope((StackScope scope) {
     final RawPointArray rawPoints = scope.convertPointArrayToNative(points);
+    final paintHandle = (paint as SkwasmPaint).toRawPaint();
     canvasDrawPoints(
       _handle,
       pointMode.index,
       rawPoints,
       points.length,
-      (paint as SkwasmPaint).handle,
+      paintHandle,
     );
+    paintDispose(paintHandle);
   });
 
   @override
@@ -280,26 +310,32 @@ class SkwasmCanvas implements SceneCanvas {
     ui.Paint paint
   ) => withStackScope((StackScope scope) {
     final RawPointArray rawPoints = scope.convertDoublesToNative(points);
+    final paintHandle = (paint as SkwasmPaint).toRawPaint();
     canvasDrawPoints(
       _handle,
       pointMode.index,
       rawPoints,
       points.length ~/ 2,
-      (paint as SkwasmPaint).handle,
+      paintHandle,
     );
+    paintDispose(paintHandle);
   });
 
   @override
   void drawVertices(
     ui.Vertices vertices,
     ui.BlendMode blendMode,
     ui.Paint paint,
-  ) => canvasDrawVertices(
-    _handle,
-    (vertices as SkwasmVertices).handle,
-    blendMode.index,
-    (paint as SkwasmPaint).handle,
-  );
+  ) {
+    final paintHandle = (paint as SkwasmPaint).toRawPaint();
+    canvasDrawVertices(
+      _handle,
+      (vertices as SkwasmVertices).handle,
+      blendMode.index,
+      paintHandle,
+    );
+    paintDispose(paintHandle);
+  }
 
   @override
   void drawAtlas(
@@ -319,6 +355,7 @@ class SkwasmCanvas implements SceneCanvas {
     final RawRect rawCullRect = cullRect != null
       ? scope.convertRectToNative(cullRect)
       : nullptr;
+    final paintHandle = (paint as SkwasmPaint).toRawPaint();
     canvasDrawAtlas(
       _handle,
       (atlas as SkwasmImage).handle,
@@ -328,8 +365,9 @@ class SkwasmCanvas implements SceneCanvas {
       transforms.length,
       (blendMode ?? ui.BlendMode.src).index,
       rawCullRect,
-      (paint as SkwasmPaint).handle,
+      paintHandle,
     );
+    paintDispose(paintHandle);
   });
 
   @override
@@ -350,6 +388,7 @@ class SkwasmCanvas implements SceneCanvas {
     final RawRect rawCullRect = cullRect != null
       ? scope.convertRectToNative(cullRect)
       : nullptr;
+    final paintHandle = (paint as SkwasmPaint).toRawPaint();
     canvasDrawAtlas(
       _handle,
       (atlas as SkwasmImage).handle,
@@ -359,8 +398,9 @@ class SkwasmCanvas implements SceneCanvas {
       rstTransforms.length ~/ 4,
       (blendMode ?? ui.BlendMode.src).index,
       rawCullRect,
-      (paint as SkwasmPaint).handle,
+      paintHandle,
     );
+    paintDispose(paintHandle);
   });
 
   @override