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

ui/cc/cc/CCLayerSorter.cpp

Index: ui/cc/cc/CCLayerSorter.cpp
diff --git a/ui/cc/cc/CCLayerSorter.cpp b/ui/cc/cc/CCLayerSorter.cpp
new file mode 100644
index 0000000000000000000000000000000000000000..fdf3c7bb275c167133fa108d11a30d1f832ae0f3
--- /dev/null
+++ b/ui/cc/cc/CCLayerSorter.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:
+ * 1.  Redistributions of source code must retain the above copyright
+ *     notice, this list of conditions and the following disclaimer.
+ * 2.  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.
+ *
+ * THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS 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 APPLE INC. OR ITS 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"
+
+#include "cc/CCLayerSorter.h"
+
+#include "cc/CCMathUtil.h"
+#include "cc/CCRenderSurface.h"
+#include <limits.h>
+#include <public/WebTransformationMatrix.h>
+#include <wtf/Deque.h>
+
+using namespace std;
+using WebKit::WebTransformationMatrix;
+
+#define LOG_CHANNEL_PREFIX Log
+#define SHOW_DEBUG_LOG 0
+
+#if !defined( NDEBUG )
+#if SHOW_DEBUG_LOG
+static WTFLogChannel LogCCLayerSorter = { 0x00000000, "", WTFLogChannelOn };
+#else
+static WTFLogChannel LogCCLayerSorter = { 0x00000000, "", WTFLogChannelOff };
+#endif
+#endif
+
+namespace WebCore {
+
+inline static float perpProduct(const FloatSize& u, const FloatSize& v)
+{
+    return u.width() * v.height() - u.height() * v.width();
+}
+
+// Tests if two edges defined by their endpoints (a,b) and (c,d) intersect. Returns true and the
+// point of intersection if they do and false otherwise.
+static bool edgeEdgeTest(const FloatPoint& a, const FloatPoint& b, const FloatPoint& c, const FloatPoint& d, FloatPoint& r)
+{
+    FloatSize u = b - a;
+    FloatSize v = d - c;
+    FloatSize w = a - c;
+
+    float denom = perpProduct(u, v);
+
+    // If denom == 0 then the edges are parallel. While they could be overlapping
+    // we don't bother to check here as the we'll find their intersections from the
+    // corner to quad tests.
+    if (!denom)
+        return false;
+
+    float s = perpProduct(v, w) / denom;
+    if (s < 0 || s > 1)
+        return false;
+
+    float t = perpProduct(u, w) / denom;
+    if (t < 0 || t > 1)
+        return false;
+
+    u.scale(s);
+    r = a + u;
+    return true;
+}
+
+// Checks whether layer "a" draws on top of layer "b". The weight value returned is an indication of
+// the maximum z-depth difference between the layers or zero if the layers are found to be intesecting
+// (some features are in front and some are behind).
+CCLayerSorter::ABCompareResult CCLayerSorter::checkOverlap(LayerShape* a, LayerShape* b, float zThreshold, float& weight)
+{
+    weight = 0;
+
+    // Early out if the projected bounds don't overlap.
+    if (!a->projectedBounds.intersects(b->projectedBounds))
+        return None;
+
+    FloatPoint aPoints[4] = {a->projectedQuad.p1(), a->projectedQuad.p2(), a->projectedQuad.p3(), a->projectedQuad.p4() };
+    FloatPoint bPoints[4] = {b->projectedQuad.p1(), b->projectedQuad.p2(), b->projectedQuad.p3(), b->projectedQuad.p4() };
+
+    // Make a list of points that inside both layer quad projections.
+    Vector<FloatPoint> overlapPoints;
+
+    // Check all four corners of one layer against the other layer's quad.
+    for (int i = 0; i < 4; ++i) {
+        if (a->projectedQuad.containsPoint(bPoints[i]))
+            overlapPoints.append(bPoints[i]);
+        if (b->projectedQuad.containsPoint(aPoints[i]))
+            overlapPoints.append(aPoints[i]);
+    }
+
+    // Check all the edges of one layer for intersection with the other layer's edges.
+    FloatPoint r;
+    for (int ea = 0; ea < 4; ++ea)
+        for (int eb = 0; eb < 4; ++eb)
+            if (edgeEdgeTest(aPoints[ea], aPoints[(ea + 1) % 4],
+                             bPoints[eb], bPoints[(eb + 1) % 4],
+                             r))
+                overlapPoints.append(r);
+
+    if (!overlapPoints.size())
+        return None;
+
+    // Check the corresponding layer depth value for all overlap points to determine
+    // which layer is in front.
+    float maxPositive = 0;
+    float maxNegative = 0;
+    for (unsigned o = 0; o < overlapPoints.size(); o++) {
+        float za = a->layerZFromProjectedPoint(overlapPoints[o]);
+        float zb = b->layerZFromProjectedPoint(overlapPoints[o]);
+
+        float diff = za - zb;
+        if (diff > maxPositive)
+            maxPositive = diff;
+        if (diff < maxNegative)
+            maxNegative = diff;
+    }
+
+    float maxDiff = (fabsf(maxPositive) > fabsf(maxNegative) ? maxPositive : maxNegative);
+
+    // If the results are inconsistent (and the z difference substantial to rule out
+    // numerical errors) then the layers are intersecting. We will still return an
+    // order based on the maximum depth difference but with an edge weight of zero
+    // these layers will get priority if a graph cycle is present and needs to be broken.
+    if (maxPositive > zThreshold && maxNegative < -zThreshold)
+        weight = 0;
+    else
+        weight = fabsf(maxDiff);
+
+    // Maintain relative order if the layers have the same depth at all intersection points.
+    if (maxDiff <= 0)
+        return ABeforeB;
+
+    return BBeforeA;
+}
+
+CCLayerSorter::LayerShape::LayerShape(float width, float height, const WebTransformationMatrix& drawTransform)
+{
+    FloatQuad layerQuad(FloatPoint(-width * 0.5, height * 0.5),
+                        FloatPoint(width * 0.5, height * 0.5),
+                        FloatPoint(width * 0.5, -height * 0.5),
+                        FloatPoint(-width * 0.5, -height * 0.5));
+
+    // Compute the projection of the layer quad onto the z = 0 plane.
+
+    FloatPoint clippedQuad[8];
+    int numVerticesInClippedQuad;
+    CCMathUtil::mapClippedQuad(drawTransform, layerQuad, clippedQuad, numVerticesInClippedQuad);
+
+    if (numVerticesInClippedQuad < 3) {
+        projectedBounds = FloatRect();
+        return;
+    }
+
+    projectedBounds = CCMathUtil::computeEnclosingRectOfVertices(clippedQuad, numVerticesInClippedQuad);
+
+    // NOTE: it will require very significant refactoring and overhead to deal with
+    // generalized polygons or multiple quads per layer here. For the sake of layer
+    // sorting it is equally correct to take a subsection of the polygon that can be made
+    // into a quad. This will only be incorrect in the case of intersecting layers, which
+    // are not supported yet anyway.
+    projectedQuad.setP1(clippedQuad[0]);
+    projectedQuad.setP2(clippedQuad[1]);
+    projectedQuad.setP3(clippedQuad[2]);
+    if (numVerticesInClippedQuad >= 4)
+        projectedQuad.setP4(clippedQuad[3]);
+    else
+        projectedQuad.setP4(clippedQuad[2]); // this will be a degenerate quad that is actually a triangle.
+
+    // Compute the normal of the layer's plane.
+    FloatPoint3D c1 = drawTransform.mapPoint(FloatPoint3D(0, 0, 0));
+    FloatPoint3D c2 = drawTransform.mapPoint(FloatPoint3D(0, 1, 0));
+    FloatPoint3D c3 = drawTransform.mapPoint(FloatPoint3D(1, 0, 0));
+    FloatPoint3D c12 = c2 - c1;
+    FloatPoint3D c13 = c3 - c1;
+    layerNormal = c13.cross(c12);
+
+    transformOrigin = c1;
+}
+
+// Returns the Z coordinate of a point on the layer that projects
+// to point p which lies on the z = 0 plane. It does it by computing the
+// intersection of a line starting from p along the Z axis and the plane
+// of the layer.
+float CCLayerSorter::LayerShape::layerZFromProjectedPoint(const FloatPoint& p) const
+{
+    const FloatPoint3D zAxis(0, 0, 1);
+    FloatPoint3D w = FloatPoint3D(p) - transformOrigin;
+
+    float d = layerNormal.dot(zAxis);
+    float n = -layerNormal.dot(w);
+
+    // Check if layer is parallel to the z = 0 axis which will make it
+    // invisible and hence returning zero is fine.
+    if (!d)
+        return 0;
+
+    // The intersection point would be given by:
+    // p + (n / d) * u  but since we are only interested in the 
+    // z coordinate and p's z coord is zero, all we need is the value of n/d.
+    return n / d;
+}
+
+void CCLayerSorter::createGraphNodes(LayerList::iterator first, LayerList::iterator last)
+{
+#if !defined( NDEBUG )
+    LOG(CCLayerSorter, "Creating graph nodes:\n");
+#endif
+    float minZ = FLT_MAX;
+    float maxZ = -FLT_MAX;
+    for (LayerList::const_iterator it = first; it < last; it++) {
+        m_nodes.append(GraphNode(*it));
+        GraphNode& node = m_nodes.at(m_nodes.size() - 1);
+        CCRenderSurface* renderSurface = node.layer->renderSurface();
+        if (!node.layer->drawsContent() && !renderSurface)
+            continue;
+
+#if !defined( NDEBUG )
+        LOG(CCLayerSorter, "Layer %d (%d x %d)\n", node.layer->id(), node.layer->bounds().width(), node.layer->bounds().height());
+#endif
+
+        WebTransformationMatrix drawTransform;
+        float layerWidth, layerHeight;
+        if (renderSurface) {
+            drawTransform = renderSurface->drawTransform();
+            layerWidth = renderSurface->contentRect().width();
+            layerHeight = renderSurface->contentRect().height();
+        } else {
+            drawTransform = node.layer->drawTransform();
+            layerWidth = node.layer->bounds().width();
+            layerHeight = node.layer->bounds().height();
+        }
+
+        node.shape = LayerShape(layerWidth, layerHeight, drawTransform);
+
+        maxZ = max(maxZ, node.shape.transformOrigin.z());
+        minZ = min(minZ, node.shape.transformOrigin.z());
+    }
+
+    m_zRange = fabsf(maxZ - minZ);
+}
+
+void CCLayerSorter::createGraphEdges()
+{
+#if !defined( NDEBUG )
+    LOG(CCLayerSorter, "Edges:\n");
+#endif
+    // Fraction of the total zRange below which z differences
+    // are not considered reliable.
+    const float zThresholdFactor = 0.01;
+    float zThreshold = m_zRange * zThresholdFactor;
+
+    for (unsigned na = 0; na < m_nodes.size(); na++) {
+        GraphNode& nodeA = m_nodes[na];
+        if (!nodeA.layer->drawsContent() && !nodeA.layer->renderSurface())
+            continue;
+        for (unsigned nb = na + 1; nb < m_nodes.size(); nb++) {
+            GraphNode& nodeB = m_nodes[nb];
+            if (!nodeB.layer->drawsContent() && !nodeB.layer->renderSurface())
+                continue;
+            float weight = 0;
+            ABCompareResult overlapResult = checkOverlap(&nodeA.shape, &nodeB.shape, zThreshold, weight);
+            GraphNode* startNode = 0;
+            GraphNode* endNode = 0;
+            if (overlapResult == ABeforeB) {
+                startNode = &nodeA;
+                endNode = &nodeB;
+            } else if (overlapResult == BBeforeA) {
+                startNode = &nodeB;
+                endNode = &nodeA;
+            }
+
+            if (startNode) {
+#if !defined( NDEBUG )
+                LOG(CCLayerSorter, "%d -> %d\n", startNode->layer->id(), endNode->layer->id());
+#endif
+                m_edges.append(GraphEdge(startNode, endNode, weight));
+            }
+        }
+    }
+
+    for (unsigned i = 0; i < m_edges.size(); i++) {
+        GraphEdge& edge = m_edges[i];
+        m_activeEdges.add(&edge, &edge);
+        edge.from->outgoing.append(&edge);
+        edge.to->incoming.append(&edge);
+        edge.to->incomingEdgeWeight += edge.weight;
+    }
+}
+
+// Finds and removes an edge from the list by doing a swap with the
+// last element of the list.
+void CCLayerSorter::removeEdgeFromList(GraphEdge* edge, Vector<GraphEdge*>& list)
+{
+    size_t edgeIndex = list.find(edge);
+    ASSERT(edgeIndex != notFound);
+    if (list.size() == 1) {
+        ASSERT(!edgeIndex);
+        list.clear();
+        return;
+    }
+    if (edgeIndex != list.size() - 1)
+        list[edgeIndex] = list[list.size() - 1];
+
+    list.removeLast();
+}
+
+// Sorts the given list of layers such that they can be painted in a back-to-front
+// order. Sorting produces correct results for non-intersecting layers that don't have
+// cyclical order dependencies. Cycles and intersections are broken (somewhat) aribtrarily.
+// Sorting of layers is done via a topological sort of a directed graph whose nodes are
+// the layers themselves. An edge from node A to node B signifies that layer A needs to
+// be drawn before layer B. If A and B have no dependency between each other, then we
+// preserve the ordering of those layers as they were in the original list.
+//
+// The draw order between two layers is determined by projecting the two triangles making
+// up each layer quad to the Z = 0 plane, finding points of intersection between the triangles
+// and backprojecting those points to the plane of the layer to determine the corresponding Z
+// coordinate. The layer with the lower Z coordinate (farther from the eye) needs to be rendered
+// first.
+//
+// If the layer projections don't intersect, then no edges (dependencies) are created
+// between them in the graph. HOWEVER, in this case we still need to preserve the ordering
+// of the original list of layers, since that list should already have proper z-index
+// ordering of layers.
+//
+void CCLayerSorter::sort(LayerList::iterator first, LayerList::iterator last)
+{
+#if !defined( NDEBUG )
+    LOG(CCLayerSorter, "Sorting start ----\n");
+#endif
+    createGraphNodes(first, last);
+
+    createGraphEdges();
+
+    Vector<GraphNode*> sortedList;
+    Deque<GraphNode*> noIncomingEdgeNodeList;
+
+    // Find all the nodes that don't have incoming edges.
+    for (NodeList::iterator la = m_nodes.begin(); la < m_nodes.end(); la++) {
+        if (!la->incoming.size())
+            noIncomingEdgeNodeList.append(la);
+    }
+
+#if !defined( NDEBUG )
+    LOG(CCLayerSorter, "Sorted list: ");
+#endif
+    while (m_activeEdges.size() || noIncomingEdgeNodeList.size()) {
+        while (noIncomingEdgeNodeList.size()) {
+
+            // It is necessary to preserve the existing ordering of layers, when there are
+            // no explicit dependencies (because this existing ordering has correct
+            // z-index/layout ordering). To preserve this ordering, we process Nodes in
+            // the same order that they were added to the list.
+            GraphNode* fromNode = noIncomingEdgeNodeList.takeFirst();
+
+            // Add it to the final list.
+            sortedList.append(fromNode);
+
+#if !defined( NDEBUG )
+            LOG(CCLayerSorter, "%d, ", fromNode->layer->id());
+#endif
+
+            // Remove all its outgoing edges from the graph.
+            for (unsigned i = 0; i < fromNode->outgoing.size(); i++) {
+                GraphEdge* outgoingEdge = fromNode->outgoing[i];
+
+                m_activeEdges.remove(outgoingEdge);
+                removeEdgeFromList(outgoingEdge, outgoingEdge->to->incoming);
+                outgoingEdge->to->incomingEdgeWeight -= outgoingEdge->weight;
+
+                if (!outgoingEdge->to->incoming.size())
+                    noIncomingEdgeNodeList.append(outgoingEdge->to);
+            }
+            fromNode->outgoing.clear();
+        }
+
+        if (!m_activeEdges.size())
+            break;
+
+        // If there are still active edges but the list of nodes without incoming edges
+        // is empty then we have run into a cycle. Break the cycle by finding the node
+        // with the smallest overall incoming edge weight and use it. This will favor
+        // nodes that have zero-weight incoming edges i.e. layers that are being
+        // occluded by a layer that intersects them.
+        float minIncomingEdgeWeight = FLT_MAX;
+        GraphNode* nextNode = 0;
+        for (unsigned i = 0; i < m_nodes.size(); i++) {
+            if (m_nodes[i].incoming.size() && m_nodes[i].incomingEdgeWeight < minIncomingEdgeWeight) {
+                minIncomingEdgeWeight = m_nodes[i].incomingEdgeWeight;
+                nextNode = &m_nodes[i];
+            }
+        }
+        ASSERT(nextNode);
+        // Remove all its incoming edges.
+        for (unsigned e = 0; e < nextNode->incoming.size(); e++) {
+            GraphEdge* incomingEdge = nextNode->incoming[e];
+
+            m_activeEdges.remove(incomingEdge);
+            removeEdgeFromList(incomingEdge, incomingEdge->from->outgoing);
+        }
+        nextNode->incoming.clear();
+        nextNode->incomingEdgeWeight = 0;
+        noIncomingEdgeNodeList.append(nextNode);
+#if !defined( NDEBUG )
+        LOG(CCLayerSorter, "Breaking cycle by cleaning up incoming edges from %d (weight = %f)\n", nextNode->layer->id(), minIncomingEdgeWeight);
+#endif
+    }
+
+    // Note: The original elements of the list are in no danger of having their ref count go to zero
+    // here as they are all nodes of the layer hierarchy and are kept alive by their parent nodes.
+    int count = 0;
+    for (LayerList::iterator it = first; it < last; it++)
+        *it = sortedList[count++]->layer;
+
+#if !defined( NDEBUG )
+    LOG(CCLayerSorter, "Sorting end ----\n");
+#endif
+
+    m_nodes.clear();
+    m_edges.clear();
+    m_activeEdges.clear();
+}
+
+}