Improve Aura overdraw by changing hole calculation

ui/gfx/compositor/layer.cc

 // Copyright (c) 2011 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 "ui/gfx/compositor/layer.h"
 
 #include <algorithm>
 
 #include "base/logging.h"
 #include "base/memory/scoped_ptr.h"
@@ skipping 296 matching lines @@
     invalid_rect_ = gfx::Rect();
     return;
   }
   scoped_ptr<gfx::Canvas> canvas(gfx::Canvas::CreateCanvas(
       draw_rect.width(), draw_rect.height(), false));
   canvas->TranslateInt(-draw_rect.x(), -draw_rect.y());
   delegate_->OnPaintLayer(canvas.get());
   SetCanvas(*canvas->GetSkCanvas(), draw_rect.origin());
 }
 
-void Layer::RecomputeHole() {
-  if (type_ == LAYER_HAS_NO_TEXTURE)
+void Layer::ClearHoleRects() {
+  hole_rect_ = gfx::Rect();
+
+  for (size_t i = 0; i < children_.size(); i++)
+    children_[i]->ClearHoleRects();
+}
+
+void Layer::GeneratePreorderTraversal(
+    std::vector<ui::Layer*>* layer_traversal) {
+  if (!visible_)
     return;
 
-  // Reset to default.
-  hole_rect_ = gfx::Rect();
+  if (fills_bounds_opaquely_ && type_ == LAYER_HAS_TEXTURE)
+    layer_traversal->push_back(this);
 
-  // Find the largest hole
-  for (size_t i = 0; i < children_.size(); ++i) {
-    // Ignore non-opaque and hidden children.
-    if (!children_[i]->IsCompletelyOpaque() || !children_[i]->visible_)
-      continue;
+  for (size_t i = 0; i < children_.size(); i++)
+    children_[i]->GeneratePreorderTraversal(layer_traversal);
+}
 
-    // Ignore children that aren't rotated by multiples of 90 degrees.
-    float degrees;
-    if (!InterpolatedTransform::FactorTRS(children_[i]->transform(),
-                                          NULL, &degrees, NULL) ||
-        !IsApproximateMultilpleOf(degrees, 90.0f))
-      continue;
-
-    // The reason why we don't just take the bounds and apply the transform is
-    // that the bounds encodes a position, too, so the effective transformation
-    // matrix is actually different that the one reported. As well, the bounds
-    // will not necessarily be at the origin.
-    gfx::Rect candidate_hole(children_[i]->bounds_.size());
-    ui::Transform transform = children_[i]->transform();
-    transform.ConcatTranslate(static_cast<float>(children_[i]->bounds_.x()),
-                              static_cast<float>(children_[i]->bounds_.y()));
-    transform.TransformRect(&candidate_hole);
-
-    // This layer might not contain the child (e.g., a portion of the child may
-    // be offscreen). Only the portion of the child that overlaps this layer is
-    // of any importance, so take the intersection.
-    candidate_hole = gfx::Rect(bounds().size()).Intersect(candidate_hole);
-
-    // Ensure we have the largest hole.
-    if (candidate_hole.size().GetArea() > hole_rect_.size().GetArea())
-      hole_rect_ = candidate_hole;
+void Layer::RecomputeHole() {

[sky, 2011/10/24 15:44:52]

I don't like all the tree walking we do on any interesting change. Imagine if
during one animation cycle we changed the bounds of a bunch of layers.
Could we instead set a boolean indicating we need to update the regions to paint
and then in DrawTree update them?

+  Layer* root_layer = this;
+  while (root_layer->parent_) {
+    root_layer = root_layer->parent_;
   }
 
-  // Free up texture memory if the hole fills bounds of layer.
-  if (!ShouldDraw() && !layer_updated_externally_)
-    texture_ = NULL;
-}
+  std::vector<ui::Layer*> layer_traversal;
+  root_layer->ClearHoleRects();
+  root_layer->GeneratePreorderTraversal(&layer_traversal);
 
-bool Layer::IsCompletelyOpaque() const {
-  return fills_bounds_opaquely() && GetCombinedOpacity() == 1.0f;
+  for (size_t i = 0; i < layer_traversal.size(); i++) {
+    Layer* layer = layer_traversal[i];
+    gfx::Rect bounds = gfx::Rect(layer->bounds().size());
+    ui::Transform layer_transform;
+    layer->GetTransformRelativeTo(root_layer, &layer_transform);
+
+    // Iterate through layers which are after layer_traversal[i] in draw order
+    // and find the largest candidate hole.
+    for (size_t j = i + 1; j < layer_traversal.size(); j++) {
+      gfx::Rect candidate_hole = gfx::Rect(layer_traversal[j]->bounds().size());
+
+      // Compute transform to go from bounds of layer |j| to local bounds of layer |i|.

[sky, 2011/10/24 15:44:52]

This line is > 80 chars

+      ui::Transform candidate_hole_transform;
+      layer_traversal[j]->GetTransformRelativeTo(root_layer,

[sky, 2011/10/24 15:44:52]

This is a lot of transform building. Rather than having
GeneratePreorderTraversal generate Layers, maybe it should generate:
struct {
  Transform transform_relative_to_root;
  Layer* layer;
}

+          &candidate_hole_transform);
+      if (!layer_transform.Invert())
+        continue;
+      candidate_hole_transform.ConcatTransform(layer_transform);
+
+      // cannot punch a hole if the relative transform between the two layers
+      // is not multiple of 90.
+      float degrees;
+      if (!InterpolatedTransform::FactorTRS(candidate_hole_transform, NULL,
+          &degrees, NULL) || !IsApproximateMultilpleOf(degrees, 90.0f))
+        continue;
+
+      // can only punch a hole if the two layers have the same opacity.
+      if (layer->GetCombinedOpacity() !=
+          layer_traversal[j]->GetCombinedOpacity())

[Ian Vollick, 2011/10/22 01:06:03]

Shouldn't we punch a hole only if layer_traversal[j]->GetCombinedOpacity() is
1.0? Otherwise, we'd still see a bit of layer i under layer j, wouldn't we?

+        continue;
+
+      candidate_hole_transform.TransformRect(&candidate_hole);
+      candidate_hole = candidate_hole.Intersect(bounds);
+
+      if (candidate_hole.size().GetArea() > layer->hole_rect().size().GetArea())
+        layer->set_hole_rect(candidate_hole);
+    }
+    // Free up texture memory if the hole fills bounds of layer.
+    if (!layer->ShouldDraw() && !layer_updated_externally())
+      layer->DropTexture();
+  }
 }
 
 // static
 void Layer::PunchHole(const gfx::Rect& rect,
                       const gfx::Rect& region_to_punch_out,
                       std::vector<gfx::Rect>* sides) {
   gfx::Rect trimmed_rect = rect.Intersect(region_to_punch_out);
 
   if (trimmed_rect.IsEmpty()) {
     sides->push_back(rect);
@@ skipping 18 matching lines @@
                              rect.right() - trimmed_rect.right(),
                              trimmed_rect.height()));
 
   // Bottom (below the hole).
   sides->push_back(gfx::Rect(rect.x(),
                              trimmed_rect.bottom(),
                              rect.width(),
                              rect.bottom() - trimmed_rect.bottom()));
 }
 
+void Layer::DropTexture() {
+  if (!layer_updated_externally_)
+    texture_ = NULL;
+}
+
 void Layer::DropTextures() {
   if (!layer_updated_externally_)
     texture_ = NULL;
   for (size_t i = 0; i < children_.size(); ++i)
     children_[i]->DropTextures();
 }
 
 bool Layer::ConvertPointForAncestor(const Layer* ancestor,
                                     gfx::Point* point) const {
   ui::Transform transform;
@@ skipping 57 matching lines @@
 }
 
 void Layer::SetTransformImmediately(const ui::Transform& transform) {
   transform_ = transform;
 
   if (parent())
     parent()->RecomputeHole();
 }
 
 void Layer::SetOpacityImmediately(float opacity) {
-  bool was_opaque = GetCombinedOpacity() == 1.0f;
   opacity_ = opacity;
-  bool is_opaque = GetCombinedOpacity() == 1.0f;
-
-  // If our opacity has changed we need to recompute our hole, our parent's hole
-  // and the holes of all our descendants.
-  if (was_opaque != is_opaque) {
-    if (parent_)
-      parent_->RecomputeHole();
-    std::queue<Layer*> to_process;
-    to_process.push(this);
-    while (!to_process.empty()) {
-      Layer* current = to_process.front();
-      to_process.pop();
-      current->RecomputeHole();
-      for (size_t i = 0; i < current->children_.size(); ++i)
-        to_process.push(current->children_.at(i));
-    }
-  }
+  if (parent_)
+    parent_->RecomputeHole();
 }
 
 void Layer::SetBoundsFromAnimator(const gfx::Rect& bounds) {
   SetBoundsImmediately(bounds);
 }
 
 void Layer::SetTransformFromAnimator(const Transform& transform) {
   SetTransformImmediately(transform);
 }
 
@@ skipping 67 matching lines @@
     result.append(", style=filled");
 
   return result;
 }
 
 #endif
 
 ////////////////////////////////////////////////////////////////////////////////
 
 }  // namespace ui