[canvaskit] Makes access to CkSurface null-safer (flutter/engine#54895)

Handles exceptions coming from `MakeSWCanvasSurface` and `MakeOffscreenSWCanvasSurface`.

Also makes surface size a member of `CkSurface` to make sure that it's always in sync with `surface`.

Fixes https://github.com/flutter/flutter/issues/154402

[C++, Objective-C, Java style guides]: https://github.com/flutter/engine/blob/main/CONTRIBUTING.md#style

engine/src/flutter/lib/web_ui/lib/src/engine/canvaskit/surface.dart

@@ -71,6 +71,10 @@ class Surface extends DisplayCanvas {
   bool _contextLost = false;
   bool get debugContextLost => _contextLost;
 
+  /// Forces AssertionError when attempting to create a CPU-based surface.
+  /// Only for tests.
+  bool debugThrowOnSoftwareSurfaceCreation = false;
+
   /// A cached copy of the most recently created `webglcontextlost` listener.
   ///
   /// We must cache this function because each time we access the tear-off it
@@ -182,7 +186,6 @@ class Surface extends DisplayCanvas {
   }
 
   BitmapSize? _currentCanvasPhysicalSize;
-  BitmapSize? _currentSurfaceSize;
 
   /// Sets the CSS size of the canvas so that canvas pixels are 1:1 with device
   /// pixels.
@@ -250,7 +253,7 @@ class Surface extends DisplayCanvas {
     if (!_forceNewContext) {
       // Check if the window is the same size as before, and if so, don't allocate
       // a new canvas as the previous canvas is big enough to fit everything.
-      final BitmapSize? previousSurfaceSize = _currentSurfaceSize;
+      final BitmapSize? previousSurfaceSize = _surface?._size;
       if (previousSurfaceSize != null &&
           size.width == previousSurfaceSize.width &&
           size.height == previousSurfaceSize.height) {
@@ -299,10 +302,8 @@ class Surface extends DisplayCanvas {
       _currentCanvasPhysicalSize = size;
     }
 
-    _currentSurfaceSize = size;
     _surface?.dispose();
-    _surface = _createNewSurface(size);
+    return _surface = _createNewSurface(size);
-    return _surface!;
   }
 
   JSVoid _contextRestoredListener(DomEvent event) {
@@ -462,11 +463,17 @@ class Surface extends DisplayCanvas {
   CkSurface _createNewSurface(BitmapSize size) {
     assert(_offscreenCanvas != null || _canvasElement != null);
     if (webGLVersion == -1) {
-      return _makeSoftwareCanvasSurface('WebGL support not detected');
+      return _makeSoftwareCanvasSurface('WebGL support not detected', size);
     } else if (configuration.canvasKitForceCpuOnly) {
-      return _makeSoftwareCanvasSurface('CPU rendering forced by application');
+      return _makeSoftwareCanvasSurface(
+        'CPU rendering forced by application',
+        size,
+      );
     } else if (_glContext == 0) {
-      return _makeSoftwareCanvasSurface('Failed to initialize WebGL context');
+      return _makeSoftwareCanvasSurface(
+        'Failed to initialize WebGL context',
+        size,
+      );
     } else {
       final SkSurface? skSurface = canvasKit.MakeOnScreenGLSurface(
           _grContext!,
@@ -477,31 +484,37 @@ class Surface extends DisplayCanvas {
           _stencilBits);
 
       if (skSurface == null) {
-        return _makeSoftwareCanvasSurface('Failed to initialize WebGL surface');
+        return _makeSoftwareCanvasSurface(
+          'Failed to initialize WebGL surface',
+          size,
+        );
       }
 
-      return CkSurface(skSurface, _glContext);
+      return CkSurface(skSurface, _glContext, size);
     }
   }
 
   static bool _didWarnAboutWebGlInitializationFailure = false;
 
-  CkSurface _makeSoftwareCanvasSurface(String reason) {
+  CkSurface _makeSoftwareCanvasSurface(String reason, BitmapSize size) {
     if (!_didWarnAboutWebGlInitializationFailure) {
       printWarning('WARNING: Falling back to CPU-only rendering. $reason.');
       _didWarnAboutWebGlInitializationFailure = true;
     }
 
+    try {
+      assert(!debugThrowOnSoftwareSurfaceCreation);
+
       SkSurface surface;
       if (useOffscreenCanvas) {
         surface = canvasKit.MakeOffscreenSWCanvasSurface(_offscreenCanvas!);
       } else {
         surface = canvasKit.MakeSWCanvasSurface(_canvasElement!);
       }
-    return CkSurface(
+      return CkSurface(surface, null, size);
-      surface,
+    } catch (error) {
-      null,
+      throw CanvasKitError('Failed to create CPU-based surface: $error.');
-    );
+    }
   }
 
   bool _presentSurface() {
@@ -534,9 +547,9 @@ class Surface extends DisplayCanvas {
       browserSupportsOffscreenCanvas && !isSafari;
 }
 
-/// A Dart wrapper around Skia's CkSurface.
+/// A Dart wrapper around Skia's SkSurface.
 class CkSurface {
-  CkSurface(this.surface, this._glContext);
+  CkSurface(this.surface, this._glContext, this._size);
 
   CkCanvas getCanvas() {
     assert(!_isDisposed, 'Attempting to use the canvas of a disposed surface');
@@ -549,6 +562,8 @@ class CkSurface {
   /// at any moment. Storing it may lead to dangling pointer bugs.
   final SkSurface surface;
 
+  final BitmapSize _size;
+
   final int? _glContext;
 
   /// Flushes the graphics to be rendered on screen.

engine/src/flutter/lib/web_ui/test/canvaskit/surface_test.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+import 'dart:js_interop';
 import 'dart:js_util' as js_util;
 
 import 'package:test/bootstrap/browser.dart';
@@ -292,6 +293,29 @@ void testMain() {
       },
       skip: !Surface.offscreenCanvasSupported,
     );
+
+    test('can recover from MakeSWCanvasSurface failure', () async {
+      debugOverrideJsConfiguration(<String, Object?>{
+        'canvasKitForceCpuOnly': true,
+      }.jsify() as JsFlutterConfiguration?);
+      addTearDown(() => debugOverrideJsConfiguration(null));
+
+      final Surface surface = Surface();
+      surface.debugThrowOnSoftwareSurfaceCreation = true;
+      expect(
+        () => surface.createOrUpdateSurface(const BitmapSize(12, 34)),
+        throwsA(isA<CanvasKitError>()),
+      );
+      await Future<void>.delayed(Duration.zero);
+
+      expect(surface.debugForceNewContext, isFalse);
+
+      surface.debugThrowOnSoftwareSurfaceCreation = false;
+      final ckSurface = surface.createOrUpdateSurface(const BitmapSize(12, 34));
+
+      expect(ckSurface.surface.width(), 12);
+      expect(ckSurface.surface.height(), 34);
+    });
   });
 }