disable GPU blur on small paths

[bsalomon, 2012-03-27 20:15:20]

This is really a continuation of Guanqun's Issue at
http://codereview.appspot.com/5726057/. Codereview only allows the Issue owner
to upload patches.

I didn't apply the bench change because IMO we should be testing both code paths
in the benchmark.

I added an animated blur slide. It draws a blurred circle with an animating
radius and blur radius. I didn't notice any popping when the switch occurs. It
does seem that the GPU is losing AA on the circle or something like that. The
edges look harsher than the raster, esp on the inner and outer blur styles.

[Stephen White, 2012-03-27 20:23:39]

This might affect some fast/canvas layout test baselines, so we should probably
give the skia gardener a heads-up.

http://codereview.appspot.com/5940045/diff/1/samplecode/SampleAnimBlur.cpp
File samplecode/SampleAnimBlur.cpp (right):

http://codereview.appspot.com/5940045/diff/1/samplecode/SampleAnimBlur.cpp#ne...
samplecode/SampleAnimBlur.cpp:3: * Copyright 2011 Google Inc.
2011 -> 2012

http://codereview.appspot.com/5940045/diff/2001/samplecode/SampleAnimBlur.cpp
File samplecode/SampleAnimBlur.cpp (right):

http://codereview.appspot.com/5940045/diff/2001/samplecode/SampleAnimBlur.cpp...
samplecode/SampleAnimBlur.cpp:3: * Copyright 2011 Google Inc.
2011 -> 2012

http://codereview.appspot.com/5940045/diff/2001/src/gpu/SkGpuDevice.cpp
File src/gpu/SkGpuDevice.cpp (right):

http://codereview.appspot.com/5940045/diff/2001/src/gpu/SkGpuDevice.cpp#newco...
src/gpu/SkGpuDevice.cpp:774: if (shouldDrawBlurWithCPU(srcRect, radius)) {
You could move the sigma computations below this check, if you like.

[Stephen White, 2012-03-27 20:25:28]

And LGTM. :)

[guanqun, 2012-03-28 08:15:23]

I haven't thought about this kind of animation to switch between cpu blur and
gpu blur.

Thanks for making my patch forward! lgtm

[bsalomon, 2012-03-28 15:07:20]

Committed with Stephen's suggestions at r3514.