Efficiently handle image layer scaling

cc/picture_image_layer_impl.cc

+// Copyright 2013 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/picture_image_layer_impl.h"
+
+#include "cc/debug_colors.h"
+#include "cc/layer_tree_impl.h"
+
+namespace cc {
+
+PictureImageLayerImpl::PictureImageLayerImpl(LayerTreeImpl* treeImpl, int id)
+    : PictureLayerImpl(treeImpl, id) {
+}
+
+PictureImageLayerImpl::~PictureImageLayerImpl() {
+}
+
+const char* PictureImageLayerImpl::layerTypeAsString() const {
+  return "PictureImageLayer";
+}
+
+scoped_ptr<LayerImpl> PictureImageLayerImpl::createLayerImpl(
+    LayerTreeImpl* treeImpl) {
+  return PictureImageLayerImpl::create(treeImpl, id()).PassAs<LayerImpl>();
+}
+
+void PictureImageLayerImpl::getDebugBorderProperties(
+    SkColor* color, float* width) const {
+  *color = DebugColors::ImageLayerBorderColor();
+  *width = DebugColors::ImageLayerBorderWidth(layerTreeImpl());
+}
+
+void PictureImageLayerImpl::CalculateRasterContentsScale(
+    bool animating_transform_to_screen,
+    float* raster_contents_scale,
+    float* low_res_raster_contents_scale) {
+  // Don't scale images during rastering to ensure image quality, save memory
+  // and avoid frequent re-rastering on change of scale.
+  float min_contents_scale = layerTreeImpl()->settings().minimumContentsScale;
+  if (ideal_contents_scale_ != min_contents_scale) {

[enne (OOO), 2013/02/22 23:53:32]

No, I think this is still wrong.

min_contents_scale comes from settings and does not change.  If your ideal
contents scale is 2 and your min contents scale is 0.125, you still want to use
1 as the raster scale and not 2 as this code indicates.

[Xianzhu, 2013/02/23 00:05:20]

Yes, this is the case in the 'if' block (normally std::max(1,
min_contents_scale) == 1)

However, when ideal_contents_scale = 0.125, 0.125 instead of 1.0 is used to save
memory (the 'else' block)

[enne (OOO), 2013/02/23 01:10:55]

You convinced me in comment #13 that having low res for image layers was not a
good idea at this time until some bugs were fixed.  Therefore, I think you
should remove the if/else and always do the code in the 'if' block.

[Xianzhu, 2013/02/23 01:17:19]

Done :)

+    *raster_contents_scale = std::max(1.f, min_contents_scale);
+  } else {
+    // ... except that the contents scale is very small, to save memory.
+    *raster_contents_scale = ideal_contents_scale_;
+  }
+
+  // We don't need low res tiles.
+  *low_res_raster_contents_scale = *raster_contents_scale;
+}
+
+}  // namespace cc