Bug 794337 - Properly alias canvas image data when using Quartz compositing. r=jrmuizel

--HG--
extra : rebase_source : fb4c0e1a9bac0ac1cf54ddc23c66756060bbfdab

gfx/layers/basic/BasicCanvasLayer.cpp

@@ -109,7 +109,7 @@ BasicCanvasLayer::Initialize(const Data& aData)
     mNeedsYFlip = true;
   } else if (aData.mDrawTarget) {
     mDrawTarget = aData.mDrawTarget;
-    mSurface = gfxPlatform::GetPlatform()->GetThebesSurfaceForDrawTarget(mDrawTarget);
+    mSurface = gfxPlatform::GetPlatform()->CreateThebesSurfaceAliasForDrawTarget_hack(mDrawTarget);
     mNeedsYFlip = false;
   } else {
     NS_ERROR("CanvasLayer created without mSurface, mDrawTarget or mGLContext?");
@@ -127,8 +127,14 @@ BasicCanvasLayer::UpdateSurface(gfxASurface* aDestSurface, Layer* aMaskLayer)
 
   if (mDrawTarget) {
     mDrawTarget->Flush();
-    // TODO Fix me before turning accelerated quartz canvas by default
-    //mSurface = gfxPlatform::GetPlatform()->GetThebesSurfaceForDrawTarget(mDrawTarget);
+    if (mDrawTarget->GetType() == BACKEND_COREGRAPHICS_ACCELERATED) {
+      // We have an accelerated CG context which has changed, unlike a bitmap surface
+      // where we can alias the bits on initializing the mDrawTarget, we need to readback
+      // and copy the accelerated surface each frame. We want to support this for quick
+      // thumbnail but if we're going to be doing this every frame it likely is better
+      // to use a non accelerated (bitmap) canvas.
+      mSurface = gfxPlatform::GetPlatform()->GetThebesSurfaceForDrawTarget(mDrawTarget);
+    }
   }
 
   if (!mGLContext && aDestSurface) {

gfx/thebes/gfxPlatform.h

@@ -188,6 +188,25 @@ public:
     virtual mozilla::TemporaryRef<mozilla::gfx::ScaledFont>
       GetScaledFontForFont(mozilla::gfx::DrawTarget* aTarget, gfxFont *aFont);
 
+    /*
+     * Cairo doesn't give us a way to create a surface pointing to a context
+     * without marking it as copy on write. For canvas we want to create
+     * a surface that points to what is currently being drawn by a canvas
+     * without a copy thus we need to create a special case. This works on
+     * most platforms with GetThebesSurfaceForDrawTarget but fails on Mac
+     * because when we create the surface we vm_copy the memory and never
+     * notify the context that the canvas has drawn to it thus we end up
+     * with a static snapshot.
+     *
+     * This function guarantes that the gfxASurface reflects the DrawTarget.
+     */
+    virtual already_AddRefed<gfxASurface>
+      CreateThebesSurfaceAliasForDrawTarget_hack(mozilla::gfx::DrawTarget *aTarget) {
+      // Overwrite me on platform where GetThebesSurfaceForDrawTarget returns
+      // a snapshot of the draw target.
+      return GetThebesSurfaceForDrawTarget(aTarget);
+    }
+
     virtual already_AddRefed<gfxASurface>
       GetThebesSurfaceForDrawTarget(mozilla::gfx::DrawTarget *aTarget);
 

gfx/thebes/gfxPlatformMac.cpp

@@ -9,6 +9,7 @@
 #include "gfxQuartzSurface.h"
 #include "gfxQuartzImageSurface.h"
 #include "mozilla/gfx/2D.h"
+#include "mozilla/gfx/QuartzSupport.h"
 
 #include "gfxMacPlatformFontList.h"
 #include "gfxMacFont.h"
@@ -377,6 +378,27 @@ gfxPlatformMac::ReadAntiAliasingThreshold()
     return threshold;
 }
 
+already_AddRefed<gfxASurface>
+gfxPlatformMac::CreateThebesSurfaceAliasForDrawTarget_hack(mozilla::gfx::DrawTarget *aTarget)
+{
+  if (aTarget->GetType() == BACKEND_COREGRAPHICS) {
+    CGContextRef cg = static_cast<CGContextRef>(aTarget->GetNativeSurface(NATIVE_SURFACE_CGCONTEXT));
+    unsigned char* data = (unsigned char*)CGBitmapContextGetData(cg);
+    size_t bpp = CGBitmapContextGetBitsPerPixel(cg);
+    size_t stride = CGBitmapContextGetBytesPerRow(cg);
+    gfxIntSize size(aTarget->GetSize().width, aTarget->GetSize().height);
+    nsRefPtr<gfxImageSurface> imageSurface = new gfxImageSurface(data, size, stride, bpp == 2
+                                                                                     ? gfxImageFormat::ImageFormatRGB16_565
+                                                                                     : gfxImageFormat::ImageFormatARGB32);
+    // Here we should return a gfxQuartzImageSurface but quartz will assumes that image surfaces
+    // don't change which wont create a proper alias to the draw target, therefore we have to
+    // return a plain image surface.
+    return imageSurface.forget();
+  } else {
+    return GetThebesSurfaceForDrawTarget(aTarget);
+  }
+}
+
 already_AddRefed<gfxASurface>
 gfxPlatformMac::GetThebesSurfaceForDrawTarget(DrawTarget *aTarget)
 {

gfx/thebes/gfxPlatformMac.h

@@ -82,6 +82,9 @@ public:
 
     virtual already_AddRefed<gfxASurface>
     GetThebesSurfaceForDrawTarget(mozilla::gfx::DrawTarget *aTarget);
+
+    virtual already_AddRefed<gfxASurface>
+    CreateThebesSurfaceAliasForDrawTarget_hack(mozilla::gfx::DrawTarget *aTarget);
 private:
     virtual qcms_profile* GetPlatformCMSOutputProfile();