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// 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 <vector>
#include "base/basictypes.h"
#include "cc/base/cc_export.h"
#include "cc/base/simple_enclosed_region.h"
#include "cc/layers/layer_iterator.h"
#include "cc/trees/occlusion.h"
#include "ui/gfx/geometry/rect.h"
namespace cc {
class LayerImpl;
class Region;
class RenderSurfaceImpl;
// This class is used to track occlusion of layers while traversing them in a
// front-to-back order. As each layer is visited, one of the methods in this
// class is called to notify it about the current target surface. Then,
// occlusion in the content space of the current layer may be queried, via
// Occlusion from GetCurrentOcclusionForLayer(). If the current layer owns a
// RenderSurfaceImpl, then occlusion on that RenderSurfaceImpl may also be
// queried via surfaceOccluded() and surfaceUnoccludedContentRect(). Finally,
// once finished with the layer, occlusion behind the layer should be marked by
// calling MarkOccludedBehindLayer().
class CC_EXPORT OcclusionTracker {
explicit OcclusionTracker(const gfx::Rect& screen_space_clip_rect);
// Return an occlusion that retains the current state of the tracker
// and can be used outside of a layer walk to check occlusion.
Occlusion GetCurrentOcclusionForLayer(
const gfx::Transform& draw_transform) const;
Occlusion GetCurrentOcclusionForContributingSurface(
const gfx::Transform& draw_transform) const;
// Called at the beginning of each step in the LayerIterator's front-to-back
// traversal.
void EnterLayer(const LayerIteratorPosition& layer_iterator);
// Called at the end of each step in the LayerIterator's front-to-back
// traversal.
void LeaveLayer(const LayerIteratorPosition& layer_iterator);
// Gives the region of the screen that is not occluded by something opaque.
Region ComputeVisibleRegionInScreen() const;
void set_minimum_tracking_size(const gfx::Size& size) {
minimum_tracking_size_ = size;
struct StackObject {
StackObject() : target(0) {}
explicit StackObject(const LayerImpl* target) : target(target) {}
const LayerImpl* target;
SimpleEnclosedRegion occlusion_from_outside_target;
SimpleEnclosedRegion occlusion_from_inside_target;
// The stack holds occluded regions for subtrees in the
// RenderSurfaceImpl-Layer tree, so that when we leave a subtree we may apply
// a mask to it, but not to the parts outside the subtree.
// - The first time we see a new subtree under a target, we add that target to
// the top of the stack. This can happen as a layer representing itself, or as
// a target surface.
// - When we visit a target surface, we apply its mask to its subtree, which
// is at the top of the stack.
// - When we visit a layer representing itself, we add its occlusion to the
// current subtree, which is at the top of the stack.
// - When we visit a layer representing a contributing surface, the current
// target will never be the top of the stack since we just came from the
// contributing surface.
// We merge the occlusion at the top of the stack with the new current
// subtree. This new target is pushed onto the stack if not already there.
std::vector<StackObject> stack_;
// Called when visiting a layer representing itself. If the target was not
// already current, then this indicates we have entered a new surface subtree.
void EnterRenderTarget(const LayerImpl* new_target);
// Called when visiting a layer representing a target surface. This indicates
// we have visited all the layers within the surface, and we may perform any
// surface-wide operations.
void FinishedRenderTarget(const LayerImpl* finished_target);
// Called when visiting a layer representing a contributing surface. This
// indicates that we are leaving our current surface, and entering the new
// one. We then perform any operations required for merging results from the
// child subtree into its parent.
void LeaveToRenderTarget(const LayerImpl* new_target);
// Add the layer's occlusion to the tracked state.
void MarkOccludedBehindLayer(const LayerImpl* layer);
gfx::Rect screen_space_clip_rect_;
gfx::Size minimum_tracking_size_;
} // namespace cc