Support currentTransform in 2D Canvas.

Source/core/html/canvas/CanvasRenderingContext2D.cpp

 /*
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2008, 2010 Nokia Corporation and/or its subsidiary(-ies)
  * Copyright (C) 2007 Alp Toker <alp@atoker.com>
  * Copyright (C) 2008 Eric Seidel <eric@webkit.org>
  * Copyright (C) 2008 Dirk Schulze <krit@webkit.org>
  * Copyright (C) 2010 Torch Mobile (Beijing) Co. Ltd. All rights reserved.
  * Copyright (C) 2012, 2013 Intel Corporation. All rights reserved.
  * Copyright (C) 2013 Adobe Systems Incorporated. All rights reserved.
  *
@@ skipping 578 matching lines @@
         return;
     realizeSaves();
     modifiableState().m_globalComposite = op;
     modifiableState().m_globalBlend = blendMode;
     GraphicsContext* c = drawingContext();
     if (!c)
         return;
     c->setCompositeOperation(op, blendMode);
 }
 
+void CanvasRenderingContext2D::setCurrentTransform(const SVGMatrix& matrix)
+{
+    setTransform(matrix.a(), matrix.b(), matrix.c(), matrix.d(), matrix.e(), matrix.f());
+}
+
 void CanvasRenderingContext2D::scale(float sx, float sy)
 {
     GraphicsContext* c = drawingContext();
     if (!c)
         return;
     if (!state().m_invertibleCTM)
         return;
 
     if (!std::isfinite(sx) | !std::isfinite(sy))
         return;
@@ skipping 82 matching lines @@
     if (!std::isfinite(m11) | !std::isfinite(m21) | !std::isfinite(dx) | !std::isfinite(m12) | !std::isfinite(m22) | !std::isfinite(dy))
         return;
 
     AffineTransform transform(m11, m12, m21, m22, dx, dy);
     AffineTransform newTransform = state().m_transform * transform;
     if (state().m_transform == newTransform)
         return;
 
     realizeSaves();
 
+    modifiableState().m_transform = newTransform;

[Justin Novosad, 2013/10/09 17:17:04]

Interesting bug you fixed here, but is this the right way to fix it?  I am
guessing this is to fix the case of a setCurrentTransform/currentTransform
round-trip with a non-invertible matrix? With this change, in the case where the
transform is non-invertible, the transform will now be retained in the canvas
state, but won't be applied to the context because the call to c->concatCTM
below will be skipped. I think that is wrong. The canvas state and the graphics
context state should remain in sync. Probably not a big deal given Blink's
implementation of 2D canvas does not currently handle non-invertible transforms
correctly, but it is something we should eventually fix, and we can start right
here.

[dshwang, 2013/10/09 17:48:20]

exactly. This change is only for currentTransform with a non-invertible matrix.
We already have some inconsistent states between canvas and GraphicsContext
For example,
1. canvas calls save() lazily
2. When Canvas.currentTransform is identity, GraphicsContext.CTM is
HTMLCanvasElement::baseTransform()

In addtion, we never use non-invertible modifiableState().m_transform because we
always check modifiableState().m_invertibleCTM before using
modifiableState().m_transform.
IMO there will be nothing that we should eventually fix.


Nevertheless, if we are afraid this approach, there would be two options.
1. Add new variable to trace currentTransform although non-invertible.
  modifiableState().m_transform will be consistent with js world
  modifiableState().m_effectiveTransform will be consistent with GraphicsContext

2. Make GraphicsContext handle non-invertible matrix.
GraphicsContext can not handle non-invertible matrix. GraphicsContext just calls
SkCanvas::concat().
Introduce m_invertibleCTM in GraphicsContext and check m_invertibleCTM in every
methods before using SkCanvas like CanvasRenderingContext2D.

WDYT?

     if (!newTransform.isInvertible()) {
         modifiableState().m_invertibleCTM = false;
         return;
     }
 
-    modifiableState().m_transform = newTransform;
     c->concatCTM(transform);
     m_path.transform(transform.inverse());
 }
 
 void CanvasRenderingContext2D::resetTransform()
 {
     GraphicsContext* c = drawingContext();
     if (!c)
         return;
 
@@ skipping 1697 matching lines @@
     const int focusRingWidth = 5;
     const int focusRingOutline = 0;
     c->drawFocusRing(path, focusRingWidth, focusRingOutline, focusRingColor);
 
     c->restore();
 
     didDraw(dirtyRect);
 }
 
 } // namespace WebCore