Initial import attempt, just to play with. Many things disabled/removed

ui/cc/cc/CCDamageTracker.cpp

Index: ui/cc/cc/CCDamageTracker.cpp
diff --git a/ui/cc/cc/CCDamageTracker.cpp b/ui/cc/cc/CCDamageTracker.cpp
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index 0000000000000000000000000000000000000000..1dbb59408ed917d77f587782b1d186a7876c02cd
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+++ b/ui/cc/cc/CCDamageTracker.cpp
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+/*
+ * Copyright (C) 2011 Google Inc. All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *     * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following disclaimer
+ * in the documentation and/or other materials provided with the
+ * distribution.
+ *     * Neither the name of Google Inc. nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "config.h"
+
+#if USE(ACCELERATED_COMPOSITING)
+
+#include "cc/CCDamageTracker.h"
+
+#include "cc/CCLayerImpl.h"
+#include "cc/CCLayerTreeHostCommon.h"
+#include "cc/CCMathUtil.h"
+#include "cc/CCRenderSurface.h"
+#include <public/WebFilterOperations.h>
+
+using WebKit::WebTransformationMatrix;
+
+namespace WebCore {
+
+PassOwnPtr<CCDamageTracker> CCDamageTracker::create()
+{
+    return adoptPtr(new CCDamageTracker());
+}
+
+CCDamageTracker::CCDamageTracker()
+    : m_forceFullDamageNextUpdate(false)
+{
+    m_currentRectHistory = adoptPtr(new RectMap);
+    m_nextRectHistory = adoptPtr(new RectMap);
+}
+
+CCDamageTracker::~CCDamageTracker()
+{
+}
+
+static inline void expandRectWithFilters(FloatRect& rect, const WebKit::WebFilterOperations& filters)
+{
+    int top, right, bottom, left;
+    filters.getOutsets(top, right, bottom, left);
+    rect.move(-left, -top);
+    rect.expand(left + right, top + bottom);
+}
+
+static inline void expandDamageRectInsideRectWithFilters(FloatRect& damageRect, const FloatRect& preFilterRect, const WebKit::WebFilterOperations& filters)
+{
+    FloatRect expandedDamageRect = damageRect;
+    expandRectWithFilters(expandedDamageRect, filters);
+    FloatRect filterRect = preFilterRect;
+    expandRectWithFilters(filterRect, filters);
+
+    expandedDamageRect.intersect(filterRect);
+    damageRect.unite(expandedDamageRect);
+}
+
+void CCDamageTracker::updateDamageTrackingState(const Vector<CCLayerImpl*>& layerList, int targetSurfaceLayerID, bool targetSurfacePropertyChangedOnlyFromDescendant, const IntRect& targetSurfaceContentRect, CCLayerImpl* targetSurfaceMaskLayer, const WebKit::WebFilterOperations& filters)
+{
+    //
+    // This function computes the "damage rect" of a target surface, and updates the state
+    // that is used to correctly track damage across frames. The damage rect is the region
+    // of the surface that may have changed and needs to be redrawn. This can be used to
+    // scissor what is actually drawn, to save GPU computation and bandwidth.
+    //
+    // The surface's damage rect is computed as the union of all possible changes that
+    // have happened to the surface since the last frame was drawn. This includes:
+    //   - any changes for existing layers/surfaces that contribute to the target surface
+    //   - layers/surfaces that existed in the previous frame, but no longer exist.
+    //
+    // The basic algorithm for computing the damage region is as follows:
+    //
+    //   1. compute damage caused by changes in active/new layers
+    //       for each layer in the layerList:
+    //           if the layer is actually a renderSurface:
+    //               add the surface's damage to our target surface.
+    //           else
+    //               add the layer's damage to the target surface.
+    //
+    //   2. compute damage caused by the target surface's mask, if it exists.
+    //
+    //   3. compute damage caused by old layers/surfaces that no longer exist
+    //       for each leftover layer:
+    //           add the old layer/surface bounds to the target surface damage.
+    //
+    //   4. combine all partial damage rects to get the full damage rect.
+    //
+    // Additional important points:
+    //
+    // - This algorithm is implicitly recursive; it assumes that descendant surfaces have
+    //   already computed their damage.
+    //
+    // - Changes to layers/surfaces indicate "damage" to the target surface; If a layer is
+    //   not changed, it does NOT mean that the layer can skip drawing. All layers that
+    //   overlap the damaged region still need to be drawn. For example, if a layer
+    //   changed its opacity, then layers underneath must be re-drawn as well, even if
+    //   they did not change.
+    //
+    // - If a layer/surface property changed, the old bounds and new bounds may overlap...
+    //   i.e. some of the exposed region may not actually be exposing anything. But this
+    //   does not artificially inflate the damage rect. If the layer changed, its entire
+    //   old bounds would always need to be redrawn, regardless of how much it overlaps
+    //   with the layer's new bounds, which also need to be entirely redrawn.
+    //
+    // - See comments in the rest of the code to see what exactly is considered a "change"
+    //   in a layer/surface.
+    //
+    // - To correctly manage exposed rects, two RectMaps are maintained:
+    //
+    //      1. The "current" map contains all the layer bounds that contributed to the
+    //         previous frame (even outside the previous damaged area). If a layer changes
+    //         or does not exist anymore, those regions are then exposed and damage the
+    //         target surface. As the algorithm progresses, entries are removed from the
+    //         map until it has only leftover layers that no longer exist.
+    //
+    //      2. The "next" map starts out empty, and as the algorithm progresses, every
+    //         layer/surface that contributes to the surface is added to the map.
+    //
+    //      3. After the damage rect is computed, the two maps are swapped, so that the
+    //         damage tracker is ready for the next frame.
+    //
+
+    // These functions cannot be bypassed with early-exits, even if we know what the
+    // damage will be for this frame, because we need to update the damage tracker state
+    // to correctly track the next frame.
+    FloatRect damageFromActiveLayers = trackDamageFromActiveLayers(layerList, targetSurfaceLayerID);
+    FloatRect damageFromSurfaceMask = trackDamageFromSurfaceMask(targetSurfaceMaskLayer);
+    FloatRect damageFromLeftoverRects = trackDamageFromLeftoverRects();
+
+    FloatRect damageRectForThisUpdate;
+
+    if (m_forceFullDamageNextUpdate || targetSurfacePropertyChangedOnlyFromDescendant) {
+        damageRectForThisUpdate = targetSurfaceContentRect;
+        m_forceFullDamageNextUpdate = false;
+    } else {
+        // FIXME: can we clamp this damage to the surface's content rect? (affects performance, but not correctness)
+        damageRectForThisUpdate = damageFromActiveLayers;
+        damageRectForThisUpdate.uniteIfNonZero(damageFromSurfaceMask);
+        damageRectForThisUpdate.uniteIfNonZero(damageFromLeftoverRects);
+
+        if (filters.hasFilterThatMovesPixels())
+            expandRectWithFilters(damageRectForThisUpdate, filters);
+    }
+
+    // Damage accumulates until we are notified that we actually did draw on that frame.
+    m_currentDamageRect.uniteIfNonZero(damageRectForThisUpdate);
+
+    // The next history map becomes the current map for the next frame. Note this must
+    // happen every frame to correctly track changes, even if damage accumulates over
+    // multiple frames before actually being drawn.
+    swap(m_currentRectHistory, m_nextRectHistory);
+}
+
+FloatRect CCDamageTracker::removeRectFromCurrentFrame(int layerID, bool& layerIsNew)
+{
+    layerIsNew = !m_currentRectHistory->contains(layerID);
+
+    // take() will remove the entry from the map, or if not found, return a default (empty) rect.
+    return m_currentRectHistory->take(layerID);
+}
+
+void CCDamageTracker::saveRectForNextFrame(int layerID, const FloatRect& targetSpaceRect)
+{
+    // This layer should not yet exist in next frame's history.
+    ASSERT(m_nextRectHistory->find(layerID) == m_nextRectHistory->end());
+    m_nextRectHistory->set(layerID, targetSpaceRect);
+}
+
+FloatRect CCDamageTracker::trackDamageFromActiveLayers(const Vector<CCLayerImpl*>& layerList, int targetSurfaceLayerID)
+{
+    FloatRect damageRect = FloatRect();
+
+    for (unsigned layerIndex = 0; layerIndex < layerList.size(); ++layerIndex) {
+        // Visit layers in back-to-front order.
+        CCLayerImpl* layer = layerList[layerIndex];
+
+        if (CCLayerTreeHostCommon::renderSurfaceContributesToTarget<CCLayerImpl>(layer, targetSurfaceLayerID))
+            extendDamageForRenderSurface(layer, damageRect);
+        else
+            extendDamageForLayer(layer, damageRect);
+    }
+
+    return damageRect;
+}
+
+FloatRect CCDamageTracker::trackDamageFromSurfaceMask(CCLayerImpl* targetSurfaceMaskLayer)
+{
+    FloatRect damageRect = FloatRect();
+
+    if (!targetSurfaceMaskLayer)
+        return damageRect;
+
+    // Currently, if there is any change to the mask, we choose to damage the entire
+    // surface. This could potentially be optimized later, but it is not expected to be a
+    // common case.
+    if (targetSurfaceMaskLayer->layerPropertyChanged() || !targetSurfaceMaskLayer->updateRect().isEmpty())
+        damageRect = FloatRect(FloatPoint::zero(), FloatSize(targetSurfaceMaskLayer->bounds()));
+
+    return damageRect;
+}
+
+FloatRect CCDamageTracker::trackDamageFromLeftoverRects()
+{
+    // After computing damage for all active layers, any leftover items in the current
+    // rect history correspond to layers/surfaces that no longer exist. So, these regions
+    // are now exposed on the target surface.
+
+    FloatRect damageRect = FloatRect();
+
+    for (RectMap::iterator it = m_currentRectHistory->begin(); it != m_currentRectHistory->end(); ++it)
+        damageRect.unite(it->second);
+
+    m_currentRectHistory->clear();
+
+    return damageRect;
+}
+
+static bool layerNeedsToRedrawOntoItsTargetSurface(CCLayerImpl* layer)
+{
+    // If the layer does NOT own a surface but has SurfacePropertyChanged,
+    // this means that its target surface is affected and needs to be redrawn.
+    // However, if the layer DOES own a surface, then the SurfacePropertyChanged 
+    // flag should not be used here, because that flag represents whether the
+    // layer's surface has changed.
+    if (layer->renderSurface())
+        return layer->layerPropertyChanged();
+    return layer->layerPropertyChanged() || layer->layerSurfacePropertyChanged();
+}
+
+void CCDamageTracker::extendDamageForLayer(CCLayerImpl* layer, FloatRect& targetDamageRect)
+{
+    // There are two ways that a layer can damage a region of the target surface:
+    //   1. Property change (e.g. opacity, position, transforms):
+    //        - the entire region of the layer itself damages the surface.
+    //        - the old layer region also damages the surface, because this region is now exposed.
+    //        - note that in many cases the old and new layer rects may overlap, which is fine.
+    //
+    //   2. Repaint/update: If a region of the layer that was repainted/updated, that
+    //      region damages the surface.
+    //
+    // Property changes take priority over update rects.
+    //
+    // This method is called when we want to consider how a layer contributes to its
+    // targetRenderSurface, even if that layer owns the targetRenderSurface itself.
+    // To consider how a layer's targetSurface contributes to the ancestorSurface,
+    // extendDamageForRenderSurface() must be called instead.
+
+    // Compute the layer's "originTransform" by translating the drawTransform.
+    WebTransformationMatrix originTransform = layer->drawTransform();
+    originTransform.translate(-0.5 * layer->bounds().width(), -0.5 * layer->bounds().height());
+
+    bool layerIsNew = false;
+    FloatRect oldLayerRect = removeRectFromCurrentFrame(layer->id(), layerIsNew);
+
+    FloatRect layerRectInTargetSpace = CCMathUtil::mapClippedRect(originTransform, FloatRect(FloatPoint::zero(), layer->bounds()));
+    saveRectForNextFrame(layer->id(), layerRectInTargetSpace);
+
+    if (layerIsNew || layerNeedsToRedrawOntoItsTargetSurface(layer)) {
+        // If a layer is new or has changed, then its entire layer rect affects the target surface.
+        targetDamageRect.uniteIfNonZero(layerRectInTargetSpace);
+
+        // The layer's old region is now exposed on the target surface, too.
+        // Note oldLayerRect is already in target space.
+        targetDamageRect.uniteIfNonZero(oldLayerRect);
+    } else if (!layer->updateRect().isEmpty()) {
+        // If the layer properties havent changed, then the the target surface is only
+        // affected by the layer's update area, which could be empty.
+        FloatRect updateRectInTargetSpace = CCMathUtil::mapClippedRect(originTransform, layer->updateRect());
+        targetDamageRect.uniteIfNonZero(updateRectInTargetSpace);
+    }
+}
+
+void CCDamageTracker::extendDamageForRenderSurface(CCLayerImpl* layer, FloatRect& targetDamageRect)
+{
+    // There are two ways a "descendant surface" can damage regions of the "target surface":
+    //   1. Property change:
+    //        - a surface's geometry can change because of
+    //            - changes to descendants (i.e. the subtree) that affect the surface's content rect
+    //            - changes to ancestor layers that propagate their property changes to their entire subtree.
+    //        - just like layers, both the old surface rect and new surface rect will
+    //          damage the target surface in this case.
+    //
+    //   2. Damage rect: This surface may have been damaged by its own layerList as well, and that damage
+    //      should propagate to the target surface.
+    //
+
+    CCRenderSurface* renderSurface = layer->renderSurface();
+
+    bool surfaceIsNew = false;
+    FloatRect oldSurfaceRect = removeRectFromCurrentFrame(layer->id(), surfaceIsNew);
+
+    FloatRect surfaceRectInTargetSpace = renderSurface->drawableContentRect(); // already includes replica if it exists.
+    saveRectForNextFrame(layer->id(), surfaceRectInTargetSpace);
+
+    FloatRect damageRectInLocalSpace;
+    if (surfaceIsNew || renderSurface->surfacePropertyChanged() || layer->layerSurfacePropertyChanged()) {
+        // The entire surface contributes damage.
+        damageRectInLocalSpace = renderSurface->contentRect();
+
+        // The surface's old region is now exposed on the target surface, too.
+        targetDamageRect.uniteIfNonZero(oldSurfaceRect);
+    } else {
+        // Only the surface's damageRect will damage the target surface.
+        damageRectInLocalSpace = renderSurface->damageTracker()->currentDamageRect();
+    }
+
+    // If there was damage, transform it to target space, and possibly contribute its reflection if needed.
+    if (!damageRectInLocalSpace.isEmpty()) {
+        const WebTransformationMatrix& originTransform = renderSurface->originTransform();
+        FloatRect damageRectInTargetSpace = CCMathUtil::mapClippedRect(originTransform, damageRectInLocalSpace);
+        targetDamageRect.uniteIfNonZero(damageRectInTargetSpace);
+
+        if (layer->replicaLayer()) {
+            const WebTransformationMatrix& replicaOriginTransform = renderSurface->replicaOriginTransform();
+            targetDamageRect.uniteIfNonZero(CCMathUtil::mapClippedRect(replicaOriginTransform, damageRectInLocalSpace));
+        }
+    }
+
+    // If there was damage on the replica's mask, then the target surface receives that damage as well.
+    if (layer->replicaLayer() && layer->replicaLayer()->maskLayer()) {
+        CCLayerImpl* replicaMaskLayer = layer->replicaLayer()->maskLayer();
+
+        bool replicaIsNew = false;
+        removeRectFromCurrentFrame(replicaMaskLayer->id(), replicaIsNew);
+
+        // Compute the replica's "originTransform" that maps from the replica's origin space to the target surface origin space.
+        const WebTransformationMatrix& replicaOriginTransform = renderSurface->replicaOriginTransform();
+        FloatRect replicaMaskLayerRect = CCMathUtil::mapClippedRect(replicaOriginTransform, FloatRect(FloatPoint::zero(), FloatSize(replicaMaskLayer->bounds().width(), replicaMaskLayer->bounds().height())));
+        saveRectForNextFrame(replicaMaskLayer->id(), replicaMaskLayerRect);
+
+        // In the current implementation, a change in the replica mask damages the entire replica region.
+        if (replicaIsNew || replicaMaskLayer->layerPropertyChanged() || !replicaMaskLayer->updateRect().isEmpty())
+            targetDamageRect.uniteIfNonZero(replicaMaskLayerRect);
+    }
+
+    // If the layer has a background filter, this may cause pixels in our surface to be expanded, so we will need to expand any damage
+    // at or below this layer. We expand the damage from this layer too, as we need to readback those pixels from the surface with only
+    // the contents of layers below this one in them. This means we need to redraw any pixels in the surface being used for the blur in
+    // this layer this frame.
+    if (layer->backgroundFilters().hasFilterThatMovesPixels())
+        expandDamageRectInsideRectWithFilters(targetDamageRect, surfaceRectInTargetSpace, layer->backgroundFilters());
+}
+
+} // namespace WebCore
+
+#endif // USE(ACCELERATED_COMPOSITING)