Add helper for maintaining clip/matrix state in non-contiguous picture playback.

Review URL: https://codereview.appspot.com/6509043

git-svn-id: http://skia.googlecode.com/svn/trunk@5483 2bbb7eff-a529-9590-31e7-b0007b416f81

2 files changed, 305 insertions, 0 deletions

diff --git a/src/core/SkPictureStateTree.cpp b/src/core/SkPictureStateTree.cpp
new file mode 100644
index 0000000000..31aa00bf7a
--- /dev/null
+++ b/src/core/SkPictureStateTree.cpp
@@ -0,0 +1,176 @@
+
+/*
+ * Copyright 2012 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "SkPictureStateTree.h"
+#include "SkCanvas.h"
+
+SK_DEFINE_INST_COUNT(SkPictureStateTree)
+
+SkPictureStateTree::SkPictureStateTree()
+    : fAlloc(2048)
+    , fRoot(NULL)
+    , fStateStack(sizeof(Draw), 16) {
+    SkMatrix* identity = static_cast<SkMatrix*>(fAlloc.allocThrow(sizeof(SkMatrix)));
+    identity->reset();
+    fRoot = static_cast<Node*>(fAlloc.allocThrow(sizeof(Node)));
+    fRoot->fParent = NULL;
+    fRoot->fMatrix = identity;
+    fRoot->fFlags = Node::kSave_Flag;
+    fRoot->fOffset = 0;
+    fRoot->fLevel = 0;
+    fCurrentState.fNode = fRoot;
+    fCurrentState.fMatrix = identity;
+    *static_cast<Draw*>(fStateStack.push_back()) = fCurrentState;
+}
+
+SkPictureStateTree::~SkPictureStateTree() {
+}
+
+SkPictureStateTree::Draw* SkPictureStateTree::appendDraw(uint32_t offset) {
+    Draw* draw = static_cast<Draw*>(fAlloc.allocThrow(sizeof(Draw)));
+    *draw = fCurrentState;
+    draw->fOffset = offset;
+    return draw;
+}
+
+void SkPictureStateTree::appendSave() {
+    *static_cast<Draw*>(fStateStack.push_back()) = fCurrentState;
+    fCurrentState.fNode->fFlags |= Node::kSave_Flag;
+}
+
+void SkPictureStateTree::appendSaveLayer(uint32_t offset) {
+    *static_cast<Draw*>(fStateStack.push_back()) = fCurrentState;
+    this->appendNode(offset);
+    fCurrentState.fNode->fFlags |= Node::kSaveLayer_Flag;
+}
+
+void SkPictureStateTree::appendRestore() {
+    fCurrentState = *static_cast<Draw*>(fStateStack.back());
+    fStateStack.pop_back();
+}
+
+void SkPictureStateTree::appendTransform(const SkMatrix& trans) {
+    SkMatrix* m = static_cast<SkMatrix*>(fAlloc.allocThrow(sizeof(SkMatrix)));
+    *m = trans;
+    fCurrentState.fMatrix = m;
+}
+
+void SkPictureStateTree::appendClip(uint32_t offset) {
+    this->appendNode(offset);
+}
+
+SkPictureStateTree::Iterator SkPictureStateTree::getIterator(const SkTDArray<void*>& draws, 
+                                                             SkCanvas* canvas) {
+    return Iterator(draws, canvas, fRoot);
+}
+
+void SkPictureStateTree::appendNode(uint32_t offset) {
+    Node* n = static_cast<Node*>(fAlloc.allocThrow(sizeof(Node)));
+    n->fOffset = offset;
+    n->fFlags = 0;
+    n->fParent = fCurrentState.fNode;
+    n->fLevel = fCurrentState.fNode->fLevel + 1;
+    n->fMatrix = fCurrentState.fMatrix;
+    fCurrentState.fNode = n;
+}
+
+SkPictureStateTree::Iterator::Iterator(const SkTDArray<void*>& draws, SkCanvas* canvas, Node* root)
+    : fDraws(draws)
+    , fCanvas(canvas)
+    , fCurrentNode(root)
+    , fCurrentMatrix(NULL)
+    , fPlaybackIndex(0)
+    , fPlaybackMatrix(canvas->getTotalMatrix())
+    , fSave(false) {
+}
+
+uint32_t SkPictureStateTree::Iterator::draw() {
+    if (fPlaybackIndex >= fDraws.count()) {
+        // restore back to where we started
+        if (fCurrentNode->fFlags & Node::kSaveLayer_Flag) { fCanvas->restore(); }
+        fCurrentNode = fCurrentNode->fParent;
+        while (NULL != fCurrentNode->fParent) {
+            if (fCurrentNode->fFlags & Node::kSave_Flag) { fCanvas->restore(); }
+            if (fCurrentNode->fFlags & Node::kSaveLayer_Flag) { fCanvas->restore(); }
+            fCurrentNode = fCurrentNode->fParent;
+        }
+        fCanvas->setMatrix(fPlaybackMatrix);
+        return kDrawComplete;
+    }
+
+    Draw* draw = static_cast<Draw*>(fDraws[fPlaybackIndex]);
+    Node* targetNode = draw->fNode;
+
+    if (fSave) {
+        fCanvas->save(SkCanvas::kClip_SaveFlag);
+        fSave = false;
+    }
+
+    if (fCurrentNode != targetNode) {
+        // If we're not at the target and we don't have a list of nodes to get there, we need to
+        // figure out the path from our current node, to the target
+        if (fNodes.count() == 0) {
+            // Trace back up to a common ancestor, restoring to get our current state to match that
+            // of the ancestor, and saving a list of nodes whose state we need to apply to get to
+            // the target (we can restore up to the ancestor immediately, but we'll need to return
+            // an offset for each node on the way down to the target, to apply the desired clips and
+            // saveLayers, so it may take several draw() calls before the next draw actually occurs)
+            Node* tmp = fCurrentNode;
+            Node* ancestor = targetNode;
+            while (tmp != ancestor) {
+                uint16_t currentLevel = tmp->fLevel;
+                uint16_t targetLevel = ancestor->fLevel;
+                if (currentLevel >= targetLevel) {
+                    if (tmp != fCurrentNode && tmp->fFlags & Node::kSave_Flag) { fCanvas->restore(); }
+                    if (tmp->fFlags & Node::kSaveLayer_Flag) { fCanvas->restore(); }
+                    tmp = tmp->fParent;
+                }
+                if (currentLevel <= targetLevel) {
+                    fNodes.push(ancestor);
+                    ancestor = ancestor->fParent;
+                }
+            }
+
+            if (ancestor->fFlags & Node::kSave_Flag) {
+                if (fCurrentNode != ancestor) { fCanvas->restore(); }
+                if (targetNode != ancestor) { fCanvas->save(SkCanvas::kClip_SaveFlag); }
+            }
+            fCurrentNode = ancestor;
+        }
+
+        // If we're not at the target node yet, we'll need to return an offset to make the caller
+        // apply the next clip or saveLayer.
+        if (fCurrentNode != targetNode) {
+            if (fCurrentMatrix != fNodes.top()->fMatrix) {
+                fCurrentMatrix = fNodes.top()->fMatrix;
+                SkMatrix tmp = *fNodes.top()->fMatrix;
+                tmp.postConcat(fPlaybackMatrix);
+                fCanvas->setMatrix(tmp);
+            }
+            uint32_t offset = fNodes.top()->fOffset;
+            fCurrentNode = fNodes.top();
+            fSave = fCurrentNode != targetNode && fCurrentNode->fFlags & Node::kSave_Flag;
+            fNodes.pop();
+            return offset;
+        }
+    }
+
+    // If we got this far, the clip/saveLayer state is all set, so we can proceed to set the matrix
+    // for the draw, and return its offset.
+
+    if (fCurrentMatrix != draw->fMatrix) {
+        SkMatrix tmp = *draw->fMatrix;
+        tmp.postConcat(fPlaybackMatrix);
+        fCanvas->setMatrix(tmp);
+        fCurrentMatrix = draw->fMatrix;
+    }
+
+    ++fPlaybackIndex;
+    return draw->fOffset;
+}
+
diff --git a/src/core/SkPictureStateTree.h b/src/core/SkPictureStateTree.h
new file mode 100644
index 0000000000..a4fb8871b5
--- /dev/null
+++ b/src/core/SkPictureStateTree.h
@@ -0,0 +1,129 @@
+
+/*
+ * Copyright 2012 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#ifndef SkPictureStateTree_DEFINED
+#define SkPictureStateTree_DEFINED
+
+#include "SkTDArray.h"
+#include "SkChunkAlloc.h"
+#include "SkDeque.h"
+#include "SkMatrix.h"
+#include "SkRefCnt.h"
+
+class SkCanvas;
+
+/**
+ * Provides an interface that, given a sequence of draws into an SkPicture with corresponding
+ * offsets, allows for playback of an arbitrary subset of the draws (note that Z-order is only
+ * guaranteed if the draws are explicitly sorted).
+ */
+class SkPictureStateTree : public SkRefCnt {
+private:
+    struct Node;
+public:
+    SK_DECLARE_INST_COUNT(SkPictureStateTree)
+
+    /**
+     * A draw call, stores offset into command buffer, a pointer to the matrix, and a pointer to
+     * the node in the tree that corresponds to its clip/layer state
+     */
+    struct Draw {
+        SkMatrix* fMatrix;
+        Node* fNode;
+        uint32_t fOffset;
+        bool operator<(const Draw& other) { return fOffset < other.fOffset; }
+    };
+
+    class Iterator;
+
+    SkPictureStateTree();
+    ~SkPictureStateTree();
+
+    /** 
+     * Creates and returns a struct representing a draw at the given offset.
+     */
+    Draw* appendDraw(uint32_t offset);
+
+    /**
+     * Given a list of draws, and a canvas, returns an iterator that produces the correct sequence
+     * of offsets into the command buffer to carry out those calls with correct matrix/clip state.
+     * This handles saves/restores, and does all necessary matrix setup.
+     */
+    Iterator getIterator(const SkTDArray<void*>& draws, SkCanvas* canvas);
+
+    void appendSave();
+    void appendSaveLayer(uint32_t offset);
+    void appendRestore();
+    void appendTransform(const SkMatrix& trans);
+    void appendClip(uint32_t offset);
+
+    /**
+     * Playback helper
+     */
+    class Iterator {
+    public:
+        /** Returns the next offset into the picture stream, or kDrawComplete if complete. */
+        uint32_t draw();
+        static const uint32_t kDrawComplete = SK_MaxU32;
+    private:
+        Iterator(const SkTDArray<void*>& draws, SkCanvas* canvas, Node* root);
+        // The draws this iterator is associated with
+        const SkTDArray<void*>& fDraws;
+        // The matrix of the canvas we're playing back into
+        const SkMatrix fPlaybackMatrix;
+
+        // current state node
+        Node* fCurrentNode;
+
+        // List of nodes whose state we need to apply to reach TargetNode
+        SkTDArray<Node*> fNodes;
+        // Cache of current matrix, so we can avoid redundantly setting it
+        SkMatrix* fCurrentMatrix;
+
+        // canvas this is playing into (so we can insert saves/restores as necessary)
+        SkCanvas* fCanvas;
+
+        // current position in the array of draws
+        int fPlaybackIndex;
+        // Whether or not we need to do a save next iteration
+        bool fSave;
+
+        friend class SkPictureStateTree;
+    };
+
+private:
+
+    void appendNode(uint32_t offset);
+
+    SkChunkAlloc fAlloc;
+    Node* fRoot;
+
+    // The currently active state
+    Draw fCurrentState;
+    // A stack of states for tracking save/restores
+    SkDeque fStateStack;
+
+    // Represents a notable piece of state that requires an offset into the command buffer, 
+    // corresponding to a clip/saveLayer/etc call, to apply.
+    struct Node {
+        Node* fParent;
+        uint32_t fOffset;
+        uint16_t fLevel;
+        uint16_t fFlags;
+        SkMatrix* fMatrix;
+        enum Flags {
+            kSave_Flag      = 0x1,
+            kSaveLayer_Flag = 0x2
+        };
+    };
+
+    typedef SkRefCnt INHERITED;
+};
+
+#endif
+