Create a semi-stable API for capturing the state of an SkCanvas and reconstructing that state acros…

src/utils/SkCanvasStateUtils.cpp

Index: src/utils/SkCanvasStateUtils.cpp
diff --git a/src/utils/SkCanvasStateUtils.cpp b/src/utils/SkCanvasStateUtils.cpp
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+/*
+ * Copyright 2013 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "SkCanvasStateUtils.h"
+#include "SkCanvas.h"
+#include "SkDevice.h"
+#include "SkNWayCanvas.h"
+#include "SkWriter32.h"
+
+#define CANVAS_STATE_VERSION 1
+/*
+ * WARNING: The structs below are part of a stable ABI and as such we explicitly
+ * use unambigious primitives (e.g. int32_t instead of an enum).
+ *
+ * ANY CHANGES TO THE STRUCTS BELOW THAT IMPACT THE ABI SHOULD RESULT IN AN
+ * UPDATE OF THE CANVAS_STATE_VERSION. SUCH CHANGES SHOULD ONLY BE MADE IF
+ * ABSOLUTELY NECESSARY!
+ */
+enum RasterConfigs {
+  kUnknown_RasterConfig   = 0,
+  kRGB_565_RasterConfig   = 1,
+  kARGB_8888_RasterConfig = 2
+};
+typedef int32_t RasterConfig;
+
+enum CanvasBackends {
+    kUnknown_CanvasBackend = 0,
+    kRaster_CanvasBackend  = 1,
+    kGPU_CanvasBackend     = 2,
+    kPDF_CanvasBackend     = 3
+};
+typedef int32_t CanvasBackend;
+
+struct ClipRect {
+    int32_t left, top, right, bottom;
+};
+
+struct SkMCState {
+    float matrix[9];
+    // NOTE: this only works for non-antialiased clips
+    int32_t clipRectCount;
+    ClipRect* clipRects;
+};
+
+// NOTE: If you add more members, bump CanvasState::version.
+struct SkCanvasLayerState {
+    CanvasBackend type;
+    int32_t x, y;
+    int32_t width;
+    int32_t height;
+
+    SkMCState mcState;
+
+    union {
+        struct {
+            RasterConfig config; // pixel format: a value from RasterConfigs.
+            uint32_t rowBytes;   // Number of bytes from start of one line to next.
+            void* pixels;        // The pixels, all (height * rowBytes) of them.
+        } raster;
+        struct {
+            int32_t textureID;
+        } gpu;
+    };
+};
+
+class SkCanvasState {
+public:
+    SkCanvasState(SkCanvas* canvas) {
+        SkASSERT(canvas);
+        version = CANVAS_STATE_VERSION;
+        width = canvas->getDeviceSize().width();
+        height = canvas->getDeviceSize().height();
+        layerCount = 0;
+        layers = NULL;
+        originalCanvas = SkRef(canvas);
+
+        mcState.clipRectCount = 0;
+        mcState.clipRects = NULL;
+    }
+
+    ~SkCanvasState() {
+        // loop through the layers and free the data allocated to the clipRects
+        for (int i = 0; i < layerCount; ++i) {
+            sk_free(layers[i].mcState.clipRects);
+        }
+
+        sk_free(mcState.clipRects);
+        sk_free(layers);
+
+        // it is now safe to free the canvas since there should be no remaining
+        // references to the content that is referenced by this canvas (e.g. pixels)
+        originalCanvas->unref();
+    }
+
+    /**
+     * The version this struct was built with.  This field must always appear
+     * first in the struct so that when the versions don't match (and the
+     * remaining contents and size are potentially different) we can still
+     * compare the version numbers.
+     */
+    int32_t version;
+
+    int32_t width;
+    int32_t height;
+
+    SkMCState mcState;
+
+    int32_t layerCount;
+    SkCanvasLayerState* layers;
+
+private:
+    SkCanvas* originalCanvas;
+};
+
+////////////////////////////////////////////////////////////////////////////////
+
+class ClipValidator : public SkCanvas::ClipVisitor {
+public:
+    ClipValidator() : fFailed(false) {}
+    bool failed() { return fFailed; }
+
+    // ClipVisitor
+    virtual void clipRect(const SkRect& rect, SkRegion::Op op, bool antialias) SK_OVERRIDE {
+        fFailed |= antialias;
+    }
+
+    virtual void clipPath(const SkPath&, SkRegion::Op, bool antialias) SK_OVERRIDE {
+        fFailed |= antialias;
+    }
+
+private:
+    bool fFailed;
+};
+
+static void setup_MC_state(SkMCState* state, const SkMatrix& matrix, const SkRegion& clip) {
+    // initialize the struct
+    state->clipRectCount = 0;
+
+    // capture the matrix
+    for (int i = 0; i < 9; i++) {
+        state->matrix[i] = matrix.get(i);
+    }
+
+    /*
+     * capture the clip
+     *
+     * storage is allocated on the stack for the first 4 rects. This value was
+     * chosen somewhat arbitrarily, but does allow us to represent simple clips
+     * and some more common complex clips (e.g. a clipRect with a sub-rect
+     * clipped out of its interior) without needing to malloc any additional memory.
+     */
+    const int clipBufferSize = 4 * sizeof(ClipRect);
+    char clipBuffer[clipBufferSize];
+    SkWriter32 clipWriter(sizeof(ClipRect), clipBuffer, clipBufferSize);
+
+    if (!clip.isEmpty()) {
+        // only returns the b/w clip so aa clips fail
+        SkRegion::Iterator clip_iterator(clip);
+        for (; !clip_iterator.done(); clip_iterator.next()) {
+            // this assumes the SkIRect is stored in l,t,r,b ordering which
+            // matches the ordering of our ClipRect struct
+            clipWriter.writeIRect(clip_iterator.rect());
+            state->clipRectCount++;
+        }
+    }
+
+    // allocate memory for the clip then and copy them to the struct
+    state->clipRects = (ClipRect*) sk_malloc_throw(clipWriter.size());
+    clipWriter.flatten(state->clipRects);
+}
+
+
+
+SkCanvasState* SkCanvasStateUtils::CaptureCanvasState(SkCanvas* canvas) {
+    SkASSERT(canvas);
+
+    // Check the clip can be decomposed into rectangles (i.e. no soft clips).
+    ClipValidator validator;
+    canvas->replayClips(&validator);
+    if (validator.failed()) {
+        SkDEBUGF(("CaptureCanvasState does not support canvases with antialiased clips.\n"));
+        return NULL;
+    }
+
+    SkAutoTDelete<SkCanvasState> canvasState(SkNEW_ARGS(SkCanvasState, (canvas)));
+
+    // decompose the total matrix and clip
+    setup_MC_state(&canvasState->mcState, canvas->getTotalMatrix(), canvas->getTotalClip());
+
+    /*
+     * decompose the layers
+     *
+     * storage is allocated on the stack for the first 3 layers. It is common in
+     * some view systems (e.g. Android) that a few non-clipped layers are present
+     * and we will not need to malloc any additional memory in those cases.
+     */
+    const int layerBufferSize = 3 * sizeof(SkCanvasLayerState);
+    char layerBuffer[layerBufferSize];
+    SkWriter32 layerWriter(sizeof(SkCanvasLayerState), layerBuffer, layerBufferSize);
+    int layerCount = 0;
+    for (SkCanvas::LayerIter layer(canvas, true/*skipEmptyClips*/); !layer.done(); layer.next()) {
+
+        // we currently only work for bitmap backed devices
+        const SkBitmap& bitmap = layer.device()->accessBitmap(true/*changePixels*/);
+        if (bitmap.empty() || bitmap.isNull() || !bitmap.lockPixelsAreWritable()) {
+            return NULL;
+        }
+
+        SkCanvasLayerState* layerState =
+                (SkCanvasLayerState*) layerWriter.reserve(sizeof(SkCanvasLayerState));
+        layerState->type = kRaster_CanvasBackend;
+        layerState->x = layer.x();
+        layerState->y = layer.y();
+        layerState->width = bitmap.width();
+        layerState->height = bitmap.height();
+
+        switch (bitmap.config()) {
+            case SkBitmap::kARGB_8888_Config:
+                layerState->raster.config = kARGB_8888_RasterConfig;
+                break;
+            case SkBitmap::kRGB_565_Config:
+                layerState->raster.config = kRGB_565_RasterConfig;
+                break;
+            default:
+                return NULL;
+        }
+        layerState->raster.rowBytes = bitmap.rowBytes();
+        layerState->raster.pixels = bitmap.getPixels();
+
+        setup_MC_state(&layerState->mcState, layer.matrix(), layer.clip());
+        layerCount++;
+    }
+
+    // allocate memory for the layers and then and copy them to the struct
+    SkASSERT(layerWriter.size() == layerCount * sizeof(SkCanvasLayerState));
+    canvasState->layerCount = layerCount;
+    canvasState->layers = (SkCanvasLayerState*) sk_malloc_throw(layerWriter.size());
+    layerWriter.flatten(canvasState->layers);
+
+    // for now, just ignore any client supplied DrawFilter.
+    if (canvas->getDrawFilter()) {
+        SkDEBUGF(("CaptureCanvasState will ignore the canvases draw filter.\n"));
+    }
+
+    return canvasState.detach();
+}
+
+////////////////////////////////////////////////////////////////////////////////
+
+static void setup_canvas_from_MC_state(const SkMCState& state, SkCanvas* canvas) {
+    // reconstruct the matrix
+    SkMatrix matrix;
+    for (int i = 0; i < 9; i++) {
+        matrix.set(i, state.matrix[i]);
+    }
+
+    // reconstruct the clip
+    SkRegion clip;
+    for (int i = 0; i < state.clipRectCount; ++i) {
+        clip.op(SkIRect::MakeLTRB(state.clipRects[i].left,
+                                  state.clipRects[i].top,
+                                  state.clipRects[i].right,
+                                  state.clipRects[i].bottom),
+                SkRegion::kUnion_Op);
+    }
+
+    canvas->setMatrix(matrix);
+    canvas->setClipRegion(clip);
+}
+
+static SkCanvas* create_canvas_from_canvas_layer(const SkCanvasLayerState& layerState) {
+    SkASSERT(kRaster_CanvasBackend == layerState.type);
+
+    SkBitmap bitmap;
+    SkBitmap::Config config =
+        layerState.raster.config == kARGB_8888_RasterConfig ? SkBitmap::kARGB_8888_Config :
+        layerState.raster.config == kRGB_565_RasterConfig ? SkBitmap::kRGB_565_Config :
+        SkBitmap::kNo_Config;
+
+    if (config == SkBitmap::kNo_Config) {
+        return NULL;
+    }
+
+    bitmap.setConfig(config, layerState.width, layerState.height,
+                     layerState.raster.rowBytes);
+    bitmap.setPixels(layerState.raster.pixels);
+
+    SkASSERT(!bitmap.empty());
+    SkASSERT(!bitmap.isNull());
+
+    // create a device & canvas
+    SkAutoTUnref<SkDevice> device(SkNEW_ARGS(SkDevice, (bitmap)));
+    SkAutoTUnref<SkCanvas> canvas(SkNEW_ARGS(SkCanvas, (device.get())));
+
+    // setup the matrix and clip
+    setup_canvas_from_MC_state(layerState.mcState, canvas.get());
+
+    return canvas.detach();
+}
+
+SkCanvas* SkCanvasStateUtils::CreateFromCanvasState(const SkCanvasState* state) {
+    SkASSERT(state);
+
+    // check that the versions match
+    if (CANVAS_STATE_VERSION != state->version) {
+        SkDebugf("CreateFromCanvasState version does not match the one use to create the input");
+        return NULL;
+    }
+
+    if (state->layerCount < 1) {
+        return NULL;
+    }
+
+    SkAutoTUnref<SkNWayCanvas> canvas(SkNEW_ARGS(SkNWayCanvas, (state->width, state->height)));
+
+    // setup the matrix and clip on the n-way canvas
+    setup_canvas_from_MC_state(state->mcState, canvas);
+
+    // Iterate over the layers and add them to the n-way canvas
+    for (int i = 0; i < state->layerCount; ++i) {
+        SkAutoTUnref<SkCanvas> canvasLayer(create_canvas_from_canvas_layer(state->layers[i]));
+        if (!canvasLayer.get()) {
+            return NULL;
+        }
+        canvas->addCanvas(canvasLayer.get());
+    }
+
+    return canvas.detach();
+}
+
+////////////////////////////////////////////////////////////////////////////////
+
+void SkCanvasStateUtils::ReleaseCanvasState(SkCanvasState* state) {
+    SkDELETE(state);
+}