// 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 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.
// 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 the layers can drawn in any order and no
// edges are created between them in the graph.
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;
Vector<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()) {
// Pop the last entry from the list.
GraphNode* fromNode = noIncomingEdgeNodeList[noIncomingEdgeNodeList.size() - 1];
noIncomingEdgeNodeList.removeLast();
// Add it to the final list.
sortedList.append(fromNode);
#if !defined( NDEBUG )
LOG(CCLayerSorter, "%d, ", fromNode->layer->debugID());
#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);
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 least number incoming edges and remove them all.
unsigned minIncomingEdgeCount = UINT_MAX;
GraphNode* nextNode = 0;
for (unsigned i = 0; i < m_nodes.size(); i++) {
if (m_nodes[i].incoming.size() && (m_nodes[i].incoming.size() < minIncomingEdgeCount)) {
minIncomingEdgeCount = m_nodes[i].incoming.size();
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();
noIncomingEdgeNodeList.append(nextNode);
#if !defined( NDEBUG )
LOG(CCLayerSorter, "Breaking cycle by cleaning up %d edges from %d\n", minIncomingEdgeCount, nextNode->layer->debugID());
#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();
}
// 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->debugID());
#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->debugID(), 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();
}
