Animation start scale should be considered for the raster scale

cc/layers/picture_layer_impl.cc

Index: cc/layers/picture_layer_impl.cc
diff --git a/cc/layers/picture_layer_impl.cc b/cc/layers/picture_layer_impl.cc
index 3fb0256a7b20d13d8f77e9e94b948a275cee9031..d25867c45d45fb449253378073bad358dc7e31c5 100644
--- a/cc/layers/picture_layer_impl.cc
+++ b/cc/layers/picture_layer_impl.cc
@@ -971,12 +971,9 @@ void PictureLayerImpl::RecalculateRasterScales() {
   if (draw_properties().screen_space_transform_is_animating &&
       !ShouldAdjustRasterScaleDuringScaleAnimations()) {
     bool can_raster_at_maximum_scale = false;
-    // TODO(ajuma): If we need to deal with scale-down animations starting right
-    // as a layer gets promoted, then we'd want to have the
-    // |starting_animation_contents_scale| passed in here as a separate draw
-    // property so we could try use that when the max is too large.
-    // See crbug.com/422341.
+    bool can_raster_at_starting_scale = false;
     float maximum_scale = draw_properties().maximum_animation_contents_scale;
+    float starting_scale = draw_properties().starting_animation_contents_scale;
     if (maximum_scale) {
       gfx::Size bounds_at_maximum_scale = gfx::ToCeiledSize(
           gfx::ScaleSize(raster_source_->GetSize(), maximum_scale));
@@ -988,10 +985,23 @@ void PictureLayerImpl::RecalculateRasterScales() {
       if (maximum_area <= viewport_area)
         can_raster_at_maximum_scale = true;
     }
+    if (starting_scale && starting_scale > maximum_scale) {
+      gfx::Size bounds_at_starting_scale = gfx::ToCeiledSize(
+          gfx::ScaleSize(raster_source_->GetSize(), starting_scale));
+      int64 start_area = static_cast<int64>(bounds_at_starting_scale.width()) *
+                         static_cast<int64>(bounds_at_starting_scale.height());
+      gfx::Size viewport = layer_tree_impl()->device_viewport_size();
+      int64 viewport_area = static_cast<int64>(viewport.width()) *
+                            static_cast<int64>(viewport.height());
+      if (start_area <= viewport_area)
+        can_raster_at_starting_scale = true;
+    }
     // Use the computed scales for the raster scale directly, do not try to use
     // the ideal scale here. The current ideal scale may be way too large in the
     // case of an animation with scale, and will be constantly changing.
-    if (can_raster_at_maximum_scale)
+    if (can_raster_at_starting_scale)

[ajuma, 2015/04/23 19:17:01]

Maybe this should be 'should_raster_at_starting_scale', since it already takes
into account whether the starting scale is larger than the maximum scale?

[patro, 2015/04/24 11:47:27]

Done.

+      raster_contents_scale_ = starting_scale;
+    else if (can_raster_at_maximum_scale)

[danakj, 2015/04/23 18:24:08]

I think we want to prefer the max scale here?

[patro, 2015/04/24 11:47:27]

maximum_scale = max(all scales excluding start_scale)

For scale-down animation start_scale > max_scale so we have to raster at
starting scale to get crisp content. For remaining cases we can raster at
maximum_scale to get crisp content...Please correct me if i am wrong

       raster_contents_scale_ = maximum_scale;
     else
       raster_contents_scale_ = 1.f * ideal_page_scale_ * ideal_device_scale_;