Match html canvas which is transferred to OffscreenCanvas to CSS style

cc/layers/surface_layer_impl.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "cc/layers/surface_layer_impl.h"
 
 #include <stdint.h>
 
 #include "base/trace_event/trace_event_argument.h"
 #include "cc/debug/debug_colors.h"
 #include "cc/quads/solid_color_draw_quad.h"
 #include "cc/quads/surface_draw_quad.h"
 #include "cc/trees/layer_tree_impl.h"
 #include "cc/trees/occlusion.h"
 
 namespace cc {
 
 SurfaceLayerImpl::SurfaceLayerImpl(LayerTreeImpl* tree_impl, int id)
-    : LayerImpl(tree_impl, id), surface_scale_(0.f) {
+    : LayerImpl(tree_impl, id) {
   layer_tree_impl()->AddSurfaceLayer(this);
 }
 
 SurfaceLayerImpl::~SurfaceLayerImpl() {
   layer_tree_impl()->RemoveSurfaceLayer(this);
 }
 
 std::unique_ptr<LayerImpl> SurfaceLayerImpl::CreateLayerImpl(
     LayerTreeImpl* tree_impl) {
   return SurfaceLayerImpl::Create(tree_impl, id());
@@ skipping 16 matching lines @@
 }
 
 void SurfaceLayerImpl::SetSurfaceSize(const gfx::Size& size) {
   if (surface_size_ == size)
     return;
 
   surface_size_ = size;
   NoteLayerPropertyChanged();
 }
 
+void SurfaceLayerImpl::SetStretchContentToFillBounds(bool is_scaling_needed) {

[danakj, 2016/12/15 16:13:14]

nitto

+  if (stretch_content_to_fill_bounds_ == is_scaling_needed)
+    return;
+
+  stretch_content_to_fill_bounds_ = is_scaling_needed;
+  NoteLayerPropertyChanged();
+}
+
 void SurfaceLayerImpl::PushPropertiesTo(LayerImpl* layer) {
   LayerImpl::PushPropertiesTo(layer);
   SurfaceLayerImpl* layer_impl = static_cast<SurfaceLayerImpl*>(layer);
 
   layer_impl->SetSurfaceId(surface_id_);
   layer_impl->SetSurfaceSize(surface_size_);
   layer_impl->SetSurfaceScale(surface_scale_);
+  layer_impl->SetStretchContentToFillBounds(stretch_content_to_fill_bounds_);
 }
 
 void SurfaceLayerImpl::AppendQuads(RenderPass* render_pass,
                                    AppendQuadsData* append_quads_data) {
   AppendRainbowDebugBorder(render_pass);
 
   SharedQuadState* shared_quad_state =
       render_pass->CreateAndAppendSharedQuadState();
-  PopulateScaledSharedQuadState(shared_quad_state, surface_scale_);
+
+  if (stretch_content_to_fill_bounds_) {
+    // It is possible that the surface size and its layer bounds are changed

[danakj, 2016/12/15 16:13:14]

I think this could be more clear on its intent. While width and height can
change.. this is about them being different. How about this?

// Stretches the surface contents to exactly fill the layer bounds, regardless
of scale or aspect ratio differences.

[danakj, 2016/12/16 14:30:44]

"Strecthes" => "Stretches"

+    // changed differently on width and height. In this case, we apply a
+    // corresponding transform on the shared_quad_state.
+    float scale_x =
+        static_cast<float>(surface_size_.width()) / bounds().width();
+    float scale_y =
+        static_cast<float>(surface_size_.height()) / bounds().height();
+    PopulateScaledSharedQuadState(shared_quad_state, scale_x, scale_y);
+  } else {
+    PopulateScaledSharedQuadState(shared_quad_state, surface_scale_,
+                                  surface_scale_);
+  }
 
   if (!surface_id_.is_valid())
     return;
 
   gfx::Rect quad_rect(surface_size_);
   gfx::Rect visible_quad_rect =
       draw_properties().occlusion_in_content_space.GetUnoccludedContentRect(
           quad_rect);
+
   if (visible_quad_rect.IsEmpty())
     return;
   SurfaceDrawQuad* quad =
       render_pass->CreateAndAppendDrawQuad<SurfaceDrawQuad>();
   quad->SetNew(shared_quad_state, quad_rect, visible_quad_rect, surface_id_);
 }
 
 void SurfaceLayerImpl::GetDebugBorderProperties(SkColor* color,
                                                 float* width) const {
   *color = DebugColors::SurfaceLayerBorderColor();
@@ skipping 90 matching lines @@
 void SurfaceLayerImpl::AsValueInto(base::trace_event::TracedValue* dict) const {
   LayerImpl::AsValueInto(dict);
   dict->SetString("surface_id", surface_id_.ToString());
 }
 
 const char* SurfaceLayerImpl::LayerTypeAsString() const {
   return "cc::SurfaceLayerImpl";
 }
 
 }  // namespace cc