Transfer canvas state to the next frame with noticable restrictions.

Source/platform/graphics/RecordingImageBufferSurface.cpp

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "config.h"
 
 #include "platform/graphics/RecordingImageBufferSurface.h"
 
 #include "platform/graphics/GraphicsContext.h"
 #include "platform/graphics/ImageBuffer.h"
@@ skipping 116 matching lines @@
 
     if (!m_currentFrame) {
         return false;
     }
 
     IntRect canvasRect(IntPoint(0, 0), size());
     if (!m_frameWasCleared && !m_imageBuffer->context()->opaqueRegion().asRect().contains(canvasRect)) {
         return false;
     }
 
-    SkCanvas* oldCanvas = m_currentFrame->getRecordingCanvas(); // Could be raster or picture
+    StateStack stateStack;
 
-    // FIXME(crbug.com/392614): handle transferring complex state from the current picture to the new one.
-    if (oldCanvas->getSaveCount() > m_initialSaveCount)
+    if (!saveState(m_currentFrame->getRecordingCanvas(), &stateStack))
         return false;
 
-    if (!oldCanvas->isClipRect())
-        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(), &stateStack);
 
     m_frameWasCleared = false;
     return true;
 }
 
+bool RecordingImageBufferSurface::saveState(SkCanvas* srcCanvas, StateStack* stateStack)
+{
+    // FIXME(crbug.com/392614): handle transferring complex state from the current picture to the new one:

[zino, 2014/09/13 16:00:28]

I think you should avoid FIXME(attribution) in Blink.
http://www.chromium.org/blink/coding-style#TOC-Comments (3)

// FIXME: handle transferring complex state from the current picture to the new
one.
// Please see http://crbug.com/392614

[Sergey, 2014/09/15 02:45:36]

I think one line comment would be better... PTAL.

+    // - non-rectangular clip
+    // - non-invertible clip

[Justin Novosad, 2014/09/12 14:54:35]

I think you mean "inverted clip"?

[Sergey, 2014/09/15 02:45:36]

I meant situation, when we can't invert transform matrix to get local clip
bounds (see SkCanvas::getClipBounds). This is obsolete since the start of
SkCanvas::getClipDeviceBounds usage in this code, so, removed it.

+    if (!srcCanvas->isClipRect())
+        return false;
+
+    StateRec state;
+
+    // we will remove all the saved state stack in endRecording anyway, so it makes no difference
+    while (srcCanvas->getSaveCount() > m_initialSaveCount) {
+        state.m_ctm = srcCanvas->getTotalMatrix();
+        // FIXME(crbug.com/408392): don't mess up the state in case we will have to fallback

[zino, 2014/09/13 16:00:28]

ditto

[Sergey, 2014/09/15 02:45:36]

Done.

+        if (!srcCanvas->getClipDeviceBounds(&state.m_clip))
+            return false;
+        stateStack->push(state);
+        srcCanvas->restore();
+    }
+
+    state.m_ctm = srcCanvas->getTotalMatrix();
+    // FIXME(crbug.com/408392): don't mess up the state in case we will have to fallback

[zino, 2014/09/13 16:00:28]

ditto

[Sergey, 2014/09/15 02:45:36]

Done.

+    if (!srcCanvas->getClipDeviceBounds(&state.m_clip))
+        return false;
+    stateStack->push(state);
+
+    return true;
+}
+
+void RecordingImageBufferSurface::setCurrentState(SkCanvas* dstCanvas, StateStack* stateStack)
+{
+    while (stateStack->size() > 1) {
+        dstCanvas->resetMatrix();
+        dstCanvas->clipRect(SkRect::MakeFromIRect(stateStack->peek().m_clip));
+        dstCanvas->setMatrix(stateStack->peek().m_ctm);
+        dstCanvas->save();
+        stateStack->pop();
+    }
+
+    dstCanvas->resetMatrix();
+    dstCanvas->clipRect(SkRect::MakeFromIRect(stateStack->peek().m_clip));
+    dstCanvas->setMatrix(stateStack->peek().m_ctm);
+}
+
 } // namespace blink