cc: Fix low-res impl-side painting artifacts

cc/picture.cc

 // Copyright 2012 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 "base/debug/trace_event.h"
 #include "cc/content_layer_client.h"
 #include "cc/picture.h"
 #include "cc/rendering_stats.h"
 #include "third_party/skia/include/core/SkCanvas.h"
 #include "third_party/skia/include/core/SkData.h"
 #include "third_party/skia/include/utils/SkPictureUtils.h"
 #include "ui/gfx/rect_conversions.h"
+#include "ui/gfx/skia_util.h"
 
 namespace {
 // URI label for a lazily decoded SkPixelRef.
 const char labelLazyDecoded[] = "lazy";
 }
 
 namespace cc {
 
 scoped_refptr<Picture> Picture::Create(gfx::Rect layer_rect) {
   return make_scoped_refptr(new Picture(layer_rect));
@@ skipping 58 matching lines @@
   stats.totalPaintTimeInSeconds += delta;
   stats.totalPixelsPainted += layer_rect_.width() *
                               layer_rect_.height();
 
   canvas->restore();
   picture_->endRecording();
 
   opaque_rect_ = gfx::ToEnclosedRect(opaque_layer_rect);
 }
 
-void Picture::Raster(SkCanvas* canvas) {
+void Picture::Raster(
+    SkCanvas* canvas,
+    gfx::Rect content_rect,
+    float contents_scale) {
   TRACE_EVENT0("cc", "Picture::Raster");
   DCHECK(picture_);
+
   canvas->save();
+  canvas->clipRect(gfx::RectToSkRect(content_rect));

[danakj, 2013/01/05 00:04:58]

I find this ordering weird..

Is the scale the scale used to get to the content_rect? Should it be clipping
after the scale is applied?

[enne (OOO), 2013/01/06 03:57:18]

These are applied to the canvas, so any recorded op played back into that canvas
gets translated, scaled, then clipped, in that order.

+  canvas->scale(contents_scale, contents_scale);
   canvas->translate(layer_rect_.x(), layer_rect_.y());
   canvas->drawPicture(*picture_);
   canvas->restore();
 }
 
 void Picture::GatherPixelRefs(const gfx::Rect& rect,
                               std::list<skia::LazyPixelRef*>& result) {
   DCHECK(picture_);
   SkData* pixel_refs = SkPictureUtils::GatherPixelRefs(
       picture_.get(), SkRect::MakeXYWH(rect.x(),
@@ skipping 14 matching lines @@
     if (*refs && (*refs)->getURI() && !strncmp(
         (*refs)->getURI(), labelLazyDecoded, 4)) {
       result.push_back(static_cast<skia::LazyPixelRef*>(*refs));
     }
     refs++;
   }
   pixel_refs->unref();
 }
 
 }  // namespace cc