[web] Prevent crash when restore is called incorrectly after recording ends. (#19948)

* Prevent crash when restore is called after picture recording ends
* Addressed reviewer comments

lib/web_ui/lib/src/engine/bitmap_canvas.dart

@@ -814,7 +814,6 @@ class BitmapCanvas extends EngineCanvas {
 
   @override
   void endOfPaint() {
-    assert(_saveCount == 0);
     _canvasPool.endOfPaint();
     _elementCache?.commitFrame();
   }

lib/web_ui/lib/src/engine/surface/recording_canvas.dart

@@ -58,7 +58,7 @@ class RecordingCanvas {
   /// method for more details.
   ui.Rect? get pictureBounds {
     assert(
-      _debugRecordingEnded,
+      _recordingEnded,
       'Picture bounds not available yet. Call [endRecording] before accessing picture bounds.',
     );
     return _pictureBounds;
@@ -101,9 +101,14 @@ class RecordingCanvas {
   bool get didDraw => _didDraw;
   bool _didDraw = false;
 
-  /// When assertions are enabled used to ensure that [endRecording] is called
-  /// before calling [apply] or [pictureBounds].
-  bool _debugRecordingEnded = false;
+  /// Used to ensure that [endRecording] is called before calling [apply] or
+  /// [pictureBounds].
+  ///
+  /// When [PaintingContext] is used by [ClipContext], the painter may
+  /// end a recording and start a new one and cause [ClipContext] to call
+  /// restore on a new canvas before prior save calls, [_recordingEnded]
+  /// prevents transforms removals in that case.
+  bool _recordingEnded = false;
 
   /// Stops recording drawing commands and computes paint bounds.
   ///
@@ -114,9 +119,7 @@ class RecordingCanvas {
   /// directly it is up to you to call this method explicitly.
   void endRecording() {
     _pictureBounds = _paintBounds.computeBounds();
-    if (assertionsEnabled) {
-      _debugRecordingEnded = true;
-    }
+    _recordingEnded = true;
   }
 
   /// Applies the recorded commands onto an [engineCanvas].
@@ -126,7 +129,7 @@ class RecordingCanvas {
   /// not applied to the [engineCanvas]. A command must have a non-zero
   /// intersection with the clip in order to be applied.
   void apply(EngineCanvas? engineCanvas, ui.Rect? clipRect) {
-    assert(_debugRecordingEnded);
+    assert(_recordingEnded);
     if (_debugDumpPaintCommands) {
       final StringBuffer debugBuf = StringBuffer();
       int skips = 0;
@@ -199,14 +202,14 @@ class RecordingCanvas {
   }
 
   void save() {
-    assert(!_debugRecordingEnded);
+    assert(!_recordingEnded);
     _paintBounds.saveTransformsAndClip();
     _commands.add(const PaintSave());
     _saveCount++;
   }
 
   void saveLayerWithoutBounds(SurfacePaint paint) {
-    assert(!_debugRecordingEnded);
+    assert(!_recordingEnded);
     _hasArbitraryPaint = true;
     // TODO(het): Implement this correctly using another canvas.
     _commands.add(const PaintSave());
@@ -215,7 +218,7 @@ class RecordingCanvas {
   }
 
   void saveLayer(ui.Rect bounds, SurfacePaint paint) {
-    assert(!_debugRecordingEnded);
+    assert(!_recordingEnded);
     _hasArbitraryPaint = true;
     // TODO(het): Implement this correctly using another canvas.
     _commands.add(const PaintSave());
@@ -224,8 +227,9 @@ class RecordingCanvas {
   }
 
   void restore() {
-    assert(!_debugRecordingEnded);
-    _paintBounds.restoreTransformsAndClip();
+    if (!_recordingEnded) {
+      _paintBounds.restoreTransformsAndClip();
+    }
     if (_commands.isNotEmpty && _commands.last is PaintSave) {
       // A restore followed a save without any drawing operations in between.
       // This means that the save didn't have any effect on drawing operations
@@ -239,38 +243,38 @@ class RecordingCanvas {
   }
 
   void translate(double dx, double dy) {
-    assert(!_debugRecordingEnded);
+    assert(!_recordingEnded);
     _paintBounds.translate(dx, dy);
     _commands.add(PaintTranslate(dx, dy));
   }
 
   void scale(double sx, double sy) {
-    assert(!_debugRecordingEnded);
+    assert(!_recordingEnded);
     _paintBounds.scale(sx, sy);
     _commands.add(PaintScale(sx, sy));
   }
 
   void rotate(double radians) {
-    assert(!_debugRecordingEnded);
+    assert(!_recordingEnded);
     _paintBounds.rotateZ(radians);
     _commands.add(PaintRotate(radians));
   }
 
   void transform(Float32List matrix4) {
-    assert(!_debugRecordingEnded);
+    assert(!_recordingEnded);
     _paintBounds.transform(matrix4);
     _commands.add(PaintTransform(matrix4));
   }
 
   void skew(double sx, double sy) {
-    assert(!_debugRecordingEnded);
+    assert(!_recordingEnded);
     _hasArbitraryPaint = true;
     _paintBounds.skew(sx, sy);
     _commands.add(PaintSkew(sx, sy));
   }
 
   void clipRect(ui.Rect rect) {
-    assert(!_debugRecordingEnded);
+    assert(!_recordingEnded);
     final PaintClipRect command = PaintClipRect(rect);
     _paintBounds.clipRect(rect, command);
     _hasArbitraryPaint = true;
@@ -278,7 +282,7 @@ class RecordingCanvas {
   }
 
   void clipRRect(ui.RRect rrect) {
-    assert(!_debugRecordingEnded);
+    assert(!_recordingEnded);
     final PaintClipRRect command = PaintClipRRect(rrect);
     _paintBounds.clipRect(rrect.outerRect, command);
     _hasArbitraryPaint = true;
@@ -286,7 +290,7 @@ class RecordingCanvas {
   }
 
   void clipPath(ui.Path path, {bool doAntiAlias = true}) {
-    assert(!_debugRecordingEnded);
+    assert(!_recordingEnded);
     final PaintClipPath command = PaintClipPath(path as SurfacePath);
     _paintBounds.clipRect(path.getBounds(), command);
     _hasArbitraryPaint = true;
@@ -294,14 +298,14 @@ class RecordingCanvas {
   }
 
   void drawColor(ui.Color color, ui.BlendMode blendMode) {
-    assert(!_debugRecordingEnded);
+    assert(!_recordingEnded);
     final PaintDrawColor command = PaintDrawColor(color, blendMode);
     _commands.add(command);
     _paintBounds.grow(_paintBounds.maxPaintBounds, command);
   }
 
   void drawLine(ui.Offset p1, ui.Offset p2, SurfacePaint paint) {
-    assert(!_debugRecordingEnded);
+    assert(!_recordingEnded);
     final double paintSpread = math.max(_getPaintSpread(paint), 1.0);
     final PaintDrawLine command = PaintDrawLine(p1, p2, paint.paintData);
     // TODO(yjbanov): This can be optimized. Currently we create a box around
@@ -324,7 +328,7 @@ class RecordingCanvas {
   }
 
   void drawPaint(SurfacePaint paint) {
-    assert(!_debugRecordingEnded);
+    assert(!_recordingEnded);
     _hasArbitraryPaint = true;
     _didDraw = true;
     final PaintDrawPaint command = PaintDrawPaint(paint.paintData);
@@ -333,7 +337,7 @@ class RecordingCanvas {
   }
 
   void drawRect(ui.Rect rect, SurfacePaint paint) {
-    assert(!_debugRecordingEnded);
+    assert(!_recordingEnded);
     if (paint.shader != null) {
       _hasArbitraryPaint = true;
     }
@@ -349,7 +353,7 @@ class RecordingCanvas {
   }
 
   void drawRRect(ui.RRect rrect, SurfacePaint paint) {
-    assert(!_debugRecordingEnded);
+    assert(!_recordingEnded);
     if (paint.shader != null || !rrect.webOnlyUniformRadii) {
       _hasArbitraryPaint = true;
     }
@@ -365,7 +369,7 @@ class RecordingCanvas {
   }
 
   void drawDRRect(ui.RRect outer, ui.RRect inner, SurfacePaint paint) {
-    assert(!_debugRecordingEnded);
+    assert(!_recordingEnded);
     // Check the inner bounds are contained within the outer bounds
     // see: https://cs.chromium.org/chromium/src/third_party/skia/src/core/SkCanvas.cpp?l=1787-1789
     ui.Rect innerRect = inner.outerRect;
@@ -418,7 +422,7 @@ class RecordingCanvas {
   }
 
   void drawOval(ui.Rect rect, SurfacePaint paint) {
-    assert(!_debugRecordingEnded);
+    assert(!_recordingEnded);
     _hasArbitraryPaint = true;
     _didDraw = true;
     final double paintSpread = _getPaintSpread(paint);
@@ -432,7 +436,7 @@ class RecordingCanvas {
   }
 
   void drawCircle(ui.Offset c, double radius, SurfacePaint paint) {
-    assert(!_debugRecordingEnded);
+    assert(!_recordingEnded);
     _hasArbitraryPaint = true;
     _didDraw = true;
     final double paintSpread = _getPaintSpread(paint);
@@ -449,7 +453,7 @@ class RecordingCanvas {
   }
 
   void drawPath(ui.Path path, SurfacePaint paint) {
-    assert(!_debugRecordingEnded);
+    assert(!_recordingEnded);
     if (paint.shader == null) {
       // For Rect/RoundedRect paths use drawRect/drawRRect code paths for
       // DomCanvas optimization.
@@ -484,7 +488,7 @@ class RecordingCanvas {
   }
 
   void drawImage(ui.Image image, ui.Offset offset, SurfacePaint paint) {
-    assert(!_debugRecordingEnded);
+    assert(!_recordingEnded);
     _hasArbitraryPaint = true;
     _didDraw = true;
     final double left = offset.dx;
@@ -496,7 +500,7 @@ class RecordingCanvas {
 
   void drawImageRect(
       ui.Image image, ui.Rect src, ui.Rect dst, SurfacePaint paint) {
-    assert(!_debugRecordingEnded);
+    assert(!_recordingEnded);
     _hasArbitraryPaint = true;
     _didDraw = true;
     final PaintDrawImageRect command = PaintDrawImageRect(image, src, dst, paint.paintData);
@@ -505,7 +509,7 @@ class RecordingCanvas {
   }
 
   void drawParagraph(ui.Paragraph paragraph, ui.Offset offset) {
-    assert(!_debugRecordingEnded);
+    assert(!_recordingEnded);
     final EngineParagraph engineParagraph = paragraph as EngineParagraph;
     if (!engineParagraph._isLaidOut) {
       // Ignore non-laid out paragraphs. This matches Flutter's behavior.
@@ -531,7 +535,7 @@ class RecordingCanvas {
 
   void drawShadow(ui.Path path, ui.Color color, double elevation,
       bool transparentOccluder) {
-    assert(!_debugRecordingEnded);
+    assert(!_recordingEnded);
     _hasArbitraryPaint = true;
     _didDraw = true;
     final ui.Rect shadowRect =
@@ -543,7 +547,7 @@ class RecordingCanvas {
 
   void drawVertices(
       SurfaceVertices vertices, ui.BlendMode blendMode, SurfacePaint paint) {
-    assert(!_debugRecordingEnded);
+    assert(!_recordingEnded);
     _hasArbitraryPaint = true;
     _didDraw = true;
     final PaintDrawVertices command = PaintDrawVertices(vertices, blendMode, paint.paintData);
@@ -553,7 +557,7 @@ class RecordingCanvas {
 
   void drawRawPoints(
       ui.PointMode pointMode, Float32List points, SurfacePaint paint) {
-    assert(!_debugRecordingEnded);
+    assert(!_recordingEnded);
     _hasArbitraryPaint = true;
     _didDraw = true;
     final PaintDrawPoints command = PaintDrawPoints(pointMode, points, paint.paintData);

lib/web_ui/test/engine/recording_canvas_test.dart

@@ -187,6 +187,14 @@ void main() {
     expect(mockCanvas.methodCallLog[2].methodName, 'restore');
     expect(mockCanvas.methodCallLog[3].methodName, 'endOfPaint');
   });
+
+  // Regression test for https://github.com/flutter/flutter/issues/61697.
+  test('Allows restore calls after recording has ended', () {
+    final RecordingCanvas rc = RecordingCanvas(Rect.fromLTRB(0, 0, 200, 400));
+    rc.endRecording();
+    // Should not throw exception on restore.
+    expect(() => rc.restore(), returnsNormally);
+  });
 }
 
 // Expect a drawDRRect call to be registered in the mock call log, with the expectedArguments