Remove root_surface_transformation from PaintContext (#6213)

It should be sufficient to provide the matrix to preroll.

flow/layers/layer.h

@@ -57,7 +57,6 @@ class Layer {
 
   struct PaintContext {
     SkCanvas& canvas;
-    const SkMatrix& root_surface_transformation;
     const Stopwatch& frame_time;
     const Stopwatch& engine_time;
     TextureRegistry& texture_registry;

flow/layers/layer_tree.cc

@@ -32,7 +32,7 @@ void LayerTree::Preroll(CompositorContext::ScopedFrame& frame,
       SkRect::MakeEmpty(),
   };
 
-  root_layer_->Preroll(&context, SkMatrix::I());
+  root_layer_->Preroll(&context, frame.root_surface_transformation());
 }
 
 #if defined(OS_FUCHSIA)
@@ -63,12 +63,11 @@ void LayerTree::UpdateScene(SceneUpdateContext& context,
 void LayerTree::Paint(CompositorContext::ScopedFrame& frame) const {
   TRACE_EVENT0("flutter", "LayerTree::Paint");
   Layer::PaintContext context = {
-      *frame.canvas(),                      //
-      frame.root_surface_transformation(),  //
-      frame.context().frame_time(),         //
-      frame.context().engine_time(),        //
-      frame.context().texture_registry(),   //
-      checkerboard_offscreen_layers_        //
+      *frame.canvas(),                     //
+      frame.context().frame_time(),        //
+      frame.context().engine_time(),       //
+      frame.context().texture_registry(),  //
+      checkerboard_offscreen_layers_       //
   };
 
   if (root_layer_->needs_painting())
@@ -99,18 +98,17 @@ sk_sp<SkPicture> LayerTree::Flatten(const SkRect& bounds) {
   root_surface_transformation.reset();
 
   Layer::PaintContext paint_context = {
-      *canvas,                      // canvas
-      root_surface_transformation,  // root surface transformation
-      unused_stopwatch,             // frame time (dont care)
-      unused_stopwatch,             // engine time (dont care)
-      unused_texture_registry,      // texture registry (not supported)
-      false                         // checkerboard offscreen layers
+      *canvas,                  // canvas
+      unused_stopwatch,         // frame time (dont care)
+      unused_stopwatch,         // engine time (dont care)
+      unused_texture_registry,  // texture registry (not supported)
+      false                     // checkerboard offscreen layers
   };
 
   // Even if we don't have a root layer, we still need to create an empty
   // picture.
   if (root_layer_) {
-    root_layer_->Preroll(&preroll_context, SkMatrix::I());
+    root_layer_->Preroll(&preroll_context, root_surface_transformation);
     // The needs painting flag may be set after the preroll. So check it after.
     if (root_layer_->needs_painting()) {
       root_layer_->Paint(paint_context);

flow/layers/picture_layer.cc

@@ -45,8 +45,7 @@ void PictureLayer::Paint(PaintContext& context) const {
 #endif
 
   if (raster_cache_result_.is_valid()) {
-    raster_cache_result_.draw(context.canvas,
-                              context.root_surface_transformation);
+    raster_cache_result_.draw(context.canvas);
   } else {
     context.canvas.drawPicture(picture());
   }

flow/raster_cache.cc

@@ -17,16 +17,12 @@
 
 namespace flow {
 
-void RasterCacheResult::draw(
-    SkCanvas& canvas,
-    const SkMatrix& root_surface_transformation) const {
+void RasterCacheResult::draw(SkCanvas& canvas) const {
   SkAutoCanvasRestore auto_restore(&canvas, true);
   SkIRect bounds =
       RasterCache::GetDeviceBounds(logical_rect_, canvas.getTotalMatrix());
   FML_DCHECK(bounds.size() == image_->dimensions());
-  // Clear all transformations on the canvas except the root surface
-  // transormation.
-  canvas.setMatrix(root_surface_transformation);
+  canvas.resetMatrix();
   canvas.drawImage(image_, bounds.fLeft, bounds.fTop);
 }
 

flow/raster_cache.h

@@ -28,8 +28,7 @@ class RasterCacheResult {
 
   bool is_valid() const { return static_cast<bool>(image_); };
 
-  void draw(SkCanvas& canvas,
-            const SkMatrix& root_surface_transformation) const;
+  void draw(SkCanvas& canvas) const;
 
  private:
   sk_sp<SkImage> image_;

flow/scene_update_context.cc

@@ -187,12 +187,9 @@ SceneUpdateContext::ExecutePaintTasks(CompositorContext::ScopedFrame& frame) {
   for (auto& task : paint_tasks_) {
     FML_DCHECK(task.surface);
     SkCanvas* canvas = task.surface->GetSkiaSurface()->getCanvas();
-    Layer::PaintContext context = {*canvas,
-                                   frame.root_surface_transformation(),
-                                   frame.context().frame_time(),
+    Layer::PaintContext context = {*canvas, frame.context().frame_time(),
                                    frame.context().engine_time(),
-                                   frame.context().texture_registry(),
-                                   false};
+                                   frame.context().texture_registry(), false};
     canvas->restoreToCount(1);
     canvas->save();
     canvas->clear(task.background_color);