++

lib/web_ui/lib/src/engine/canvaskit/picture.dart

@@ -2,8 +2,12 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+import 'dart:typed_data';
+
 import 'package:ui/ui.dart' as ui;
 
+import '../../engine.dart';
+import '../configuration.dart';
 import '../profiler.dart';
 import '../util.dart';
 import 'canvas.dart';
@@ -99,7 +103,16 @@ class CkPicture extends ManagedSkiaObject<SkPicture> implements ui.Picture {
 
   @override
   ui.Image toImageSync(int width, int height) {
+    SurfaceFactory.instance.baseSurface.ensureSurface();
+    if (SurfaceFactory.instance.baseSurface.usingSoftwareBackend) {
+      return toImageSyncSoftware(width, height);
+    }
+    return toImageSyncGPU(width, height);
+  }
+
+  ui.Image toImageSyncGPU(int width, int height) {
     assert(debugCheckNotDisposed('Cannot convert picture to image.'));
+
     final CkSurface ckSurface = SurfaceFactory.instance.baseSurface
       .createRenderTargetSurface(ui.Size(width.toDouble(), height.toDouble()));
     final CkCanvas ckCanvas = ckSurface.getCanvas();
@@ -110,6 +123,31 @@ class CkPicture extends ManagedSkiaObject<SkPicture> implements ui.Picture {
     return CkImage(skImage);
   }
 
+  ui.Image toImageSyncSoftware(int width, int height) {
+    assert(debugCheckNotDisposed('Cannot convert picture to image.'));
+
+    final Surface surface = SurfaceFactory.instance.pictureToImageSurface;
+    final CkSurface ckSurface =
+      surface.createOrUpdateSurface(ui.Size(width.toDouble(), height.toDouble()));
+    final CkCanvas ckCanvas = ckSurface.getCanvas();
+    ckCanvas.clear(const ui.Color(0x00000000));
+    ckCanvas.drawPicture(this);
+    final SkImage skImage = ckSurface.surface.makeImageSnapshot();
+    final SkImageInfo imageInfo = SkImageInfo(
+      alphaType: canvasKit.AlphaType.Premul,
+      colorType: canvasKit.ColorType.RGBA_8888,
+      colorSpace: SkColorSpaceSRGB,
+      width: width.toDouble(),
+      height: height.toDouble(),
+    );
+    final Uint8List pixels = skImage.readPixels(0, 0, imageInfo);
+    final SkImage? rasterImage = canvasKit.MakeImage(imageInfo, pixels, (4 * width).toDouble());
+    if (rasterImage == null) {
+      throw StateError('Unable to convert image pixels into SkImage.');
+    }
+    return CkImage(rasterImage);
+  }
+
   @override
   bool get isResurrectionExpensive => true;
 

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

@@ -141,30 +141,34 @@ class Surface {
   ui.Size? _currentSurfaceSize;
   double _currentDevicePixelRatio = -1;
 
-  CkSurface createRenderTargetSurface(ui.Size size) {
+  /// This is only valid after the first frame or if [ensureSurface] has been
+  /// called
+  bool get usingSoftwareBackend => _glContext == null ||
+      _grContext == null || webGLVersion == -1 || !configuration.canvasKitForceCpuOnly;
+
+  /// Ensure that the initial surface, gl/grcontext have been populated so
+  /// that software rendering can be detected.
+  void ensureSurface() {
     // If the GrContext hasn't been setup yet then we need to force initialization
     // of the canvas and initial surface.
-    if (_surface == null) {
-      // TODO(jonahwilliams): this is somewhat wasteful. We should probably
-      // eagerly setup this surface instead of delaying until the first frame?
-      // Or at least cache the estimated window size.
-      createOrUpdateSurface(const ui.Size(1, 1));
-    }
-    // No context means software rendering.
-    if (_glContext == null ||_grContext == null ||
-        webGLVersion == -1 || configuration.canvasKitForceCpuOnly) {
-      return _makeSoftwareCanvasSurface(
-          htmlCanvas!, 'Failed to initialize WebGL surface');
+    if (_surface != null) {
+      return;
     }
-    final SkSurface? skSurface = canvasKit.MakeRenderTarget(
+    // TODO(jonahwilliams): this is somewhat wasteful. We should probably
+    // eagerly setup this surface instead of delaying until the first frame?
+    // Or at least cache the estimated window size.
+    createOrUpdateSurface(const ui.Size(1, 1));
+  }
+
+  /// This method is not supported if software rendering is used.
+  CkSurface createRenderTargetSurface(ui.Size size) {
+    assert(!usingSoftwareBackend);
+
+    final SkSurface skSurface = canvasKit.MakeRenderTarget(
       _grContext!,
       size.width.ceil(),
       size.height.ceil(),
-    );
-    if (skSurface == null) {
-      return _makeSoftwareCanvasSurface(
-          htmlCanvas!, 'Failed to initialize WebGL surface');
-    }
+    )!;
     return CkSurface(skSurface, _glContext);
   }
 

lib/web_ui/lib/src/engine/canvaskit/surface_factory.dart

@@ -49,6 +49,10 @@ class SurfaceFactory {
   /// The maximum number of surfaces which can be live at once.
   final int maximumSurfaces;
 
+  /// A surface used specifically for `Picture.toImage` when software rendering
+  /// is supported.
+  late final Surface pictureToImageSurface = Surface();
+
   /// The maximum number of assignable overlays.
   ///
   /// This is just `maximumSurfaces - 1` (the maximum number of surfaces minus