Change SkCanvasState to use inheritance.

src/utils/SkCanvasStateUtils.cpp

 /*
  * 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 "SkBitmapDevice.h"
@@ skipping 56 matching lines @@
             int32_t textureID;
         } gpu;
     };
 };
 
 class SkCanvasState {
 public:
     SkCanvasState(SkCanvas* canvas) {
         SkASSERT(canvas);
         version = CANVAS_STATE_VERSION;
-        width = canvas->getDeviceSize().width();
-        height = canvas->getDeviceSize().height();
+        width = canvas->getBaseLayerSize().width();
+        height = canvas->getBaseLayerSize().height();
+
+    }
+
+    virtual ~SkCanvasState() {}
+
+    /**
+     * 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;
+    int32_t alignmentPadding;
+};
+
+class SkCanvasState_v1 : public SkCanvasState {
+public:
+    SkCanvasState_v1(SkCanvas* canvas)
+    : INHERITED(canvas)
+    {
+        SkASSERT(this->version == 1);
         layerCount = 0;
         layers = NULL;
-        originalCanvas = SkRef(canvas);
-
         mcState.clipRectCount = 0;
         mcState.clipRects = NULL;
+        originalCanvas = SkRef(canvas);
     }
 
-    ~SkCanvasState() {
+    ~SkCanvasState_v1() {
         // 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;
+    typedef SkCanvasState INHERITED;
 };
 
 ////////////////////////////////////////////////////////////////////////////////
 
 class ClipValidator : public SkCanvas::ClipVisitor {
 public:
     ClipValidator() : fFailed(false) {}
     bool failed() { return fFailed; }
 
     // ClipVisitor
@@ skipping 55 matching lines @@
 
     // Check the clip can be decomposed into rectangles (i.e. no soft clips).
     ClipValidator validator;
     canvas->replayClips(&validator);
     if (validator.failed()) {
         SkErrorInternals::SetError(kInvalidOperation_SkError,
                 "CaptureCanvasState does not support canvases with antialiased clips.\n");
         return NULL;
     }
 
-    SkAutoTDelete<SkCanvasState> canvasState(SkNEW_ARGS(SkCanvasState, (canvas)));
+    SkAutoTDelete<SkCanvasState_v1> canvasState(SkNEW_ARGS(SkCanvasState_v1, (canvas)));
 
     // decompose the total matrix and clip
     setup_MC_state(&canvasState->mcState, canvas->getTotalMatrix(),
                    canvas->internal_private_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
@@ skipping 35 matching lines @@
     }
 
     // allocate memory for the layers and then and copy them to the struct
     SkASSERT(layerWriter.bytesWritten() == layerCount * sizeof(SkCanvasLayerState));
     canvasState->layerCount = layerCount;
     canvasState->layers = (SkCanvasLayerState*) sk_malloc_throw(layerWriter.bytesWritten());
     layerWriter.flatten(canvasState->layers);
 
     // for now, just ignore any client supplied DrawFilter.
     if (canvas->getDrawFilter()) {
-//        SkDEBUGF(("CaptureCanvasState will ignore the canvases draw filter.\n"));
+//        SkDEBUGF(("CaptureCanvasState will ignore the canvas's draw filter.\n"));
     }
 
     return canvasState.detach();
 }
 
 ////////////////////////////////////////////////////////////////////////////////
 
 static void setup_canvas_from_MC_state(const SkMCState& state, SkCanvas* canvas) {
     // reconstruct the matrix
     SkMatrix matrix;
@@ skipping 39 matching lines @@
 
     // 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");
+    if (state->version == 1) {
+        const SkCanvasState_v1* state_v1 = static_cast<const SkCanvasState_v1*>(state);
+
+        if (state_v1->layerCount < 1) {
+            return NULL;
+        }
+
+        SkAutoTUnref<SkCanvasStack> canvas(SkNEW_ARGS(SkCanvasStack,
+                                                      (state->width, state->height)));
+
+        // setup the matrix and clip on the n-way canvas
+        setup_canvas_from_MC_state(state_v1->mcState, canvas);
+
+        // Iterate over the layers and add them to the n-way canvas
+        for (int i = state_v1->layerCount - 1; i >= 0; --i) {
+            SkAutoTUnref<SkCanvas> cLayer(create_canvas_from_canvas_layer(state_v1->layers[i]));
+            if (!cLayer.get()) {
+                return NULL;
+            }
+            canvas->pushCanvas(cLayer.get(), SkIPoint::Make(state_v1->layers[i].x,
+                                                            state_v1->layers[i].y));
+        }
+
+        return canvas.detach();
+    } else {
+        SkDebugf("CreateFromCanvasState from version %d is not supported!", state->version);
         return NULL;
     }
-
-    if (state->layerCount < 1) {
-        return NULL;
-    }
-
-    SkAutoTUnref<SkCanvasStack> canvas(SkNEW_ARGS(SkCanvasStack, (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 = state->layerCount - 1; i >= 0; --i) {
-        SkAutoTUnref<SkCanvas> canvasLayer(create_canvas_from_canvas_layer(state->layers[i]));
-        if (!canvasLayer.get()) {
-            return NULL;
-        }
-        canvas->pushCanvas(canvasLayer.get(), SkIPoint::Make(state->layers[i].x,
-                                                             state->layers[i].y));
-    }
-
-    return canvas.detach();
 }
 
 ////////////////////////////////////////////////////////////////////////////////
 
 void SkCanvasStateUtils::ReleaseCanvasState(SkCanvasState* state) {
     SkDELETE(state);

[mtklein, 2014/07/07 20:32:40]

Can't we do the same check-version-and-static-cast trick?

[scroggo, 2014/07/07 21:44:02]

To (try to) sum up our conversation live, you want to do this for two reasons:
1. The current implementation now has two kinds of virtual-ness: A virtual
destructor and the version field.
2. It is odd to have a class with no virtual functions except for its
destructor.

Done.

 }