Image filters: implement offsets in GPU path.

Implement offset for GPU filter path. Although we can't yet use this in Blink for FEOffset, due to SVG semantics, we can use it to support crop rect (upcoming patch).

This patch adds the parameter to the filterImageGPU() signature, plumbs through the code on the GPU side, and implements support for it in SkXfermodeImageFilter for both raster and GPU.

Of the remaining filters with GPU implementations, Blur, Morphology, Bicubic and Displacement work fine; they're commutative wrt offset and can simply pass it up the chain. Blend is not, but will be removed shortly anyway (has been replaced with SkXfermodeImageFilter in Blink).

Committed: http://code.google.com/p/skia/source/detail?r=9977

[Stephen White, 2013-07-10 20:18:19]

Implement offset for GPU filter path. Although we can't yet use this in Blink
for FEOffset, due to SVG semantics, we can use it to support crop rect (upcoming
patch).

This patch adds the parameter to the filterImageGPU() signature, plumbs through
the code on the GPU side, and implements support for it in SkXfermodeImageFilter
for both raster and GPU.

Of the remaining filters with GPU implementations, Blur, Morphology, Bicubic and
Displacement work fine (they're commutative wrt offset and can simply pass it up
the chain). Blend is not, but will be removed shortly anyway (has been replaced
with SkXfermodeImageFilter in Blink).

[Stephen White, 2013-07-10 20:19:18]

PTAL. Thanks!

[bsalomon, 2013-07-10 20:26:29]

On 2013/07/10 20:19:18, Stephen White wrote:
> PTAL. Thanks!

nit: line wraps

otherwise lgtm.

[reed1, 2013-07-10 20:29:58]

what he said

[Stephen White, 2013-07-10 21:00:58]

On 2013/07/10 20:26:29, bsalomon wrote:
> On 2013/07/10 20:19:18, Stephen White wrote:
> > PTAL. Thanks!
> 
> nit: line wraps

Fixed.

> otherwise lgtm.

[commit-bot: I haz the power, 2013-07-10 21:02:25]

CQ is trying da patch. Follow status at
https://skia-tree-status.appspot.com/cq/senorblanco@chromium.org/15995026/20002

[commit-bot: I haz the power, 2013-07-10 21:22:26]

Change committed as 9977