Rasterize at maximum scale for scale animations on CPU-rasterized layers

cc/trees/layer_tree_host_common.cc

Index: cc/trees/layer_tree_host_common.cc
diff --git a/cc/trees/layer_tree_host_common.cc b/cc/trees/layer_tree_host_common.cc
index 5d0c9afc1929f57e8fa69ab66dd5e2d0b3069ff4..dd4724d53de10b57fa1e92922b613c186299e15c 100644
--- a/cc/trees/layer_tree_host_common.cc
+++ b/cc/trees/layer_tree_host_common.cc
@@ -907,10 +907,12 @@ static inline void CalculateContentsScale(LayerType* layer,
                                           float contents_scale,
                                           float device_scale_factor,
                                           float page_scale_factor,
+                                          float maximum_animation_scale_factor,
                                           bool animating_transform_to_screen) {
   layer->CalculateContentsScale(contents_scale,
                                 device_scale_factor,
                                 page_scale_factor,
+                                maximum_animation_scale_factor,
                                 animating_transform_to_screen,
                                 &layer->draw_properties().contents_scale_x,
                                 &layer->draw_properties().contents_scale_y,
@@ -922,6 +924,7 @@ static inline void CalculateContentsScale(LayerType* layer,
         contents_scale,
         device_scale_factor,
         page_scale_factor,
+        maximum_animation_scale_factor,
         animating_transform_to_screen,
         &mask_layer->draw_properties().contents_scale_x,
         &mask_layer->draw_properties().contents_scale_y,
@@ -935,6 +938,7 @@ static inline void CalculateContentsScale(LayerType* layer,
         contents_scale,
         device_scale_factor,
         page_scale_factor,
+        maximum_animation_scale_factor,
         animating_transform_to_screen,
         &replica_mask_layer->draw_properties().contents_scale_x,
         &replica_mask_layer->draw_properties().contents_scale_y,
@@ -948,11 +952,13 @@ static inline void UpdateLayerContentsScale(
     float ideal_contents_scale,
     float device_scale_factor,
     float page_scale_factor,
+    float maximum_animation_scale_factor,
     bool animating_transform_to_screen) {
   CalculateContentsScale(layer,
                          ideal_contents_scale,
                          device_scale_factor,
                          page_scale_factor,
+                         maximum_animation_scale_factor,
                          animating_transform_to_screen);
 }
 
@@ -962,6 +968,7 @@ static inline void UpdateLayerContentsScale(
     float ideal_contents_scale,
     float device_scale_factor,
     float page_scale_factor,
+    float maximum_animation_scale_factor,
     bool animating_transform_to_screen) {
   if (can_adjust_raster_scale) {
     float ideal_raster_scale =
@@ -998,6 +1005,7 @@ static inline void UpdateLayerContentsScale(
                          contents_scale,
                          device_scale_factor,
                          page_scale_factor,
+                         maximum_animation_scale_factor,
                          animating_transform_to_screen);
 
   if (layer->content_bounds() != old_content_bounds ||
@@ -1165,6 +1173,11 @@ struct DataForRecursion {
   // passed down the recursion to the children that actually use it.
   gfx::Rect clip_rect_of_target_surface_in_target_space;
 
+  // The maximum factor by which currently running animations will be
+  // scaling-up the layer during their lifetime.
+  float maximum_animation_scale_factor;
+
+  bool ancestor_is_animating_scale;
   bool ancestor_clips_subtree;
   typename LayerType::RenderSurfaceType*
       nearest_occlusion_immune_ancestor_surface;
@@ -1546,6 +1559,36 @@ static void CalculateDrawPropertiesInternal(
   ApplyPositionAdjustment(layer, data_from_ancestor.fixed_container,
       data_from_ancestor.scroll_compensation_matrix, &combined_transform);
 
+  bool layer_is_animating_scale =
+      !layer->layer_animation_controller()->HasOnlyTranslationTransforms();
+  data_for_children.ancestor_is_animating_scale =
+      layer_is_animating_scale ||
+      data_from_ancestor.ancestor_is_animating_scale;
+  float layer_maximum_animated_scale = 0.f;
+  float layer_animation_scale_factor = 1.f;
+  if (!globals.can_adjust_raster_scales ||

[Ian Vollick, 2014/04/05 02:24:33]

Can we avoid the HasOnlyTranslationTransforms work if we can't adjust raster
scales? (And all of it if data_from_ancestor.maximum_animation_scale_factor ==
0?)

I know I had bad luck with this previously, but is it hard on perf if this is
moved into a helper?

[ajuma, 2014/04/07 15:27:00]

Done.
Moved into a helper. Perftests run locally seemed fine with this.

+      !combined_transform.IsScaleOrTranslation()) {
+    layer_animation_scale_factor = 0.f;
+  } else if (layer_is_animating_scale) {
+    if (data_from_ancestor.ancestor_is_animating_scale ||

[Ian Vollick, 2014/04/05 02:24:33]

Might be worth mentioning why aren't we supporting scale accumulation. Is it
because the scales, when multiplied, could get enormous?

[ajuma, 2014/04/07 15:27:00]

Done.

+        !layer->layer_animation_controller()->MaximumScale(
+            &layer_maximum_animated_scale)) {
+      layer_animation_scale_factor = 0.f;
+    } else {
+      gfx::Vector2dF layer_transform_scales =
+          MathUtil::ComputeTransform2dScaleComponents(layer->transform(), 0.f);
+      DCHECK(layer_transform_scales != gfx::Vector2dF());
+      layer_animation_scale_factor =

[Ian Vollick, 2014/04/05 02:24:33]

This could really use a comment. It took me a while to remember that what you're
doing here is compensating for the "current" value of an in-progress scale
animation.

[ajuma, 2014/04/07 15:27:00]

Done.

+          layer_maximum_animated_scale /
+          std::max(layer_transform_scales.x(), layer_transform_scales.y());
+    }
+  }
+  float combined_maximum_animation_scale_factor =
+      layer_animation_scale_factor *
+      data_from_ancestor.maximum_animation_scale_factor;

[Ian Vollick, 2014/04/05 02:24:33]

If I'm following along correctly, the point of this code is largely so that a
scale factor of 0 propagates all the way down to the leaves. Doing this with
multiplication works, but I think it's a bit too cute; it wasn't obvious to me
that this wouldn't result in an accumulation of scale factors. Can this be made
explicit or at least a comment added?

[ajuma, 2014/04/07 15:27:00]

Removed the multiplication.

+  data_for_children.maximum_animation_scale_factor =
+      combined_maximum_animation_scale_factor;
+
   // Compute the 2d scale components of the transform hierarchy up to the target
   // surface. From there, we can decide on a contents scale for the layer.
   float layer_scale_factors = globals.device_scale_factor;
@@ -1566,8 +1609,10 @@ static void CalculateDrawPropertiesInternal(
       globals.can_adjust_raster_scales,
       ideal_contents_scale,
       globals.device_scale_factor,
-      data_from_ancestor.in_subtree_of_page_scale_application_layer ?
-          globals.page_scale_factor : 1.f,
+      data_from_ancestor.in_subtree_of_page_scale_application_layer
+          ? globals.page_scale_factor
+          : 1.f,
+      combined_maximum_animation_scale_factor,
       animating_transform_to_screen);
 
   // The draw_transform that gets computed below is effectively the layer's
@@ -2155,6 +2200,8 @@ void LayerTreeHostCommon::CalculateDrawProperties(
   data_for_recursion.clip_rect_in_target_space = device_viewport_rect;
   data_for_recursion.clip_rect_of_target_surface_in_target_space =
       device_viewport_rect;
+  data_for_recursion.maximum_animation_scale_factor = 1.f;
+  data_for_recursion.ancestor_is_animating_scale = false;
   data_for_recursion.ancestor_clips_subtree = true;
   data_for_recursion.nearest_occlusion_immune_ancestor_surface = NULL;
   data_for_recursion.in_subtree_of_page_scale_application_layer = false;
@@ -2213,6 +2260,8 @@ void LayerTreeHostCommon::CalculateDrawProperties(
   data_for_recursion.clip_rect_in_target_space = device_viewport_rect;
   data_for_recursion.clip_rect_of_target_surface_in_target_space =
       device_viewport_rect;
+  data_for_recursion.maximum_animation_scale_factor = 1.f;
+  data_for_recursion.ancestor_is_animating_scale = false;
   data_for_recursion.ancestor_clips_subtree = true;
   data_for_recursion.nearest_occlusion_immune_ancestor_surface = NULL;
   data_for_recursion.in_subtree_of_page_scale_application_layer = false;