Transfer canvas state to the next frame with noticable restrictions.

Source/platform/graphics/RecordingImageBufferSurface.cpp

Index: Source/platform/graphics/RecordingImageBufferSurface.cpp
diff --git a/Source/platform/graphics/RecordingImageBufferSurface.cpp b/Source/platform/graphics/RecordingImageBufferSurface.cpp
index 252d436f8c42e33feb8aa66c68e1426396e14e15..385a1040489ea00e315afdcb0b07c25ba7639e7a 100644
--- a/Source/platform/graphics/RecordingImageBufferSurface.cpp
+++ b/Source/platform/graphics/RecordingImageBufferSurface.cpp
@@ -16,11 +16,18 @@
 
 namespace blink {
 
+struct RecordingImageBufferSurface::StateRec {
+public:
+    SkMatrix m_ctm;
+    SkRect m_clip;
+};
+
 RecordingImageBufferSurface::RecordingImageBufferSurface(const IntSize& size, OpacityMode opacityMode)
     : ImageBufferSurface(size, opacityMode)
     , m_imageBuffer(0)
     , m_initialSaveCount(0)
     , m_frameWasCleared(true)
+    , m_stateStack(sizeof(StateRec), m_stateStackStorage, sizeof(m_stateStackStorage))
 {
     initializeCurrentFrame();
 }
@@ -118,7 +125,6 @@ bool RecordingImageBufferSurface::finalizeFrameInternal()
 {
     if (!m_imageBuffer->isDirty()) {
         if (m_currentFrame && !m_previousFrame) {
-            // Create an initial blank frame
             m_previousFrame = adoptRef(m_currentFrame->endRecording());
             initializeCurrentFrame();
         }
@@ -134,28 +140,70 @@ bool RecordingImageBufferSurface::finalizeFrameInternal()
         return false;
     }
 
-    SkCanvas* oldCanvas = m_currentFrame->getRecordingCanvas(); // Could be raster or picture
-
-    // FIXME(crbug.com/392614): handle transferring complex state from the current picture to the new one.
-    if (oldCanvas->getSaveCount() > m_initialSaveCount)
-        return false;
-
-    if (!oldCanvas->isClipRect())
+    if (!saveState(m_currentFrame->getRecordingCanvas()))
         return false;
 
-    SkMatrix ctm = oldCanvas->getTotalMatrix();
-    SkRect clip;
-    oldCanvas->getClipBounds(&clip);
-
     m_previousFrame = adoptRef(m_currentFrame->endRecording());
     initializeCurrentFrame();
 
-    SkCanvas* newCanvas = m_currentFrame->getRecordingCanvas();
-    newCanvas->concat(ctm);
-    newCanvas->clipRect(clip);
+    setCurrentState(m_currentFrame->getRecordingCanvas());
 
     m_frameWasCleared = false;
     return true;
 }
 
+bool RecordingImageBufferSurface::saveState(SkCanvas* srcCanvas)
+{
+    // FIXME(crbug.com/392614): handle transferring complex state from the current picture to the new one:
+    // - non-square clip

[Justin Novosad, 2014/08/26 16:57:20]

I think you mean non-rectangular clip 

[Sergey, 2014/08/28 09:55:33]

Done.

+    // - non-invertable clip

[Justin Novosad, 2014/08/26 16:57:20]

"non-invertible"

[Sergey, 2014/08/28 09:55:33]

Done.

+    StateRec* state = 0;
+
+    if (!srcCanvas->isClipRect())
+        return false;
+
+    while (!m_stateStack.empty()) {

[Justin Novosad, 2014/08/26 16:57:20]

You will not have to do this once you make the stack local.

[Sergey, 2014/08/28 09:55:33]

Done.

+        state = (StateRec *)m_stateStack.back();

[Justin Novosad, 2014/08/26 16:57:20]

Please avoid C-style casts.  If you switch to WTF::Deque, this will no longer be
an issue.

[Sergey, 2014/08/28 09:55:34]

Done.

+        state->~StateRec();
+        m_stateStack.pop_back();
+    }
+
+    // we will remove all the saved state stack in endRecording anyway, so it makes no difference
+    while (srcCanvas->getSaveCount() > m_initialSaveCount) {
+        state = (StateRec *)m_stateStack.push_back();
+        state->m_ctm = srcCanvas->getTotalMatrix();
+        srcCanvas->getClipBounds(&state->m_clip);
+        srcCanvas->restore();
+        if (!srcCanvas->isClipRect())
+            return false;

[Justin Novosad, 2014/08/26 16:57:20]

This needs to be fixed before we can ship display list canvas. If you don't fix
it now, please file a separate bug to it and make it a child of 386601.

[Sergey, 2014/08/28 09:55:34]

I've filed crbug.com/408392. It seems I don't have any privileges to edit
issues, so could you please make it a child of 386601. Or give me some
privileges to be able to do it on my own.

I guess I will take care of it during my next step, when I will make SKIA API to
transfer canvas state.

+    }
+
+    state = (StateRec *)m_stateStack.push_back();
+    new (state) StateRec();

[Justin Novosad, 2014/08/26 16:57:20]

No need to do this because StateRec does not even have a constructor.

[Sergey, 2014/08/28 09:55:33]

I thought that I should do that in case StateRec will be changed in future, so
that destructor call is required. Anyway, no need for this call with WTF::Deque.

+    state->m_ctm = srcCanvas->getTotalMatrix();
+    srcCanvas->getClipBounds(&state->m_clip);
+
+    return true;
+}
+
+void RecordingImageBufferSurface::setCurrentState(SkCanvas* dstCanvas)
+{
+    StateRec* state = 0;
+
+    while (m_stateStack.count() > 1) {
+        state = (StateRec *)m_stateStack.back();
+        dstCanvas->concat(state->m_ctm);
+        dstCanvas->clipRect(state->m_clip);
+        dstCanvas->save();
+        state->~StateRec();
+        m_stateStack.pop_back();
+    }
+
+    state = (StateRec *)m_stateStack.back();
+    dstCanvas->concat(state->m_ctm);
+    dstCanvas->clipRect(state->m_clip);
+    state->~StateRec();
+    m_stateStack.pop_back();
+}
+
 } // namespace blink