fix slowness of getImageData() for CanvasRenderingContext2D in linux due to un-optimized format for…

fix slowness of getImageData() for CanvasRenderingContext2D in linux due to un-optimized format for glReadPixels

This is a continuation of https://codereview.chromium.org/15331003/

BUG=242093
Committed: http://code.google.com/p/skia/source/detail?r=9280

[bsalomon, 2013-05-22 15:01:34]

Patch was originally authored by jun.a.jiang@intel.com (see
https://codereview.chromium.org/15331003/)

My version is mostly just style and comment changes.

[robertphillips, 2013-05-22 15:33:24]

lgtm + 1 nit

https://codereview.chromium.org/15746007/diff/1005/src/gpu/gl/GrGpuGL.cpp
File src/gpu/gl/GrGpuGL.cpp (right):

https://codereview.chromium.org/15746007/diff/1005/src/gpu/gl/GrGpuGL.cpp#new...
src/gpu/gl/GrGpuGL.cpp:271: return kBGRA_8888_GrPixelConfig;
seems like there is an extra set of parens in here

[Jun Jiang, 2013-05-22 17:27:20]

https://codereview.chromium.org/15746007/diff/1005/src/gpu/gl/GrGpuGL.cpp
File src/gpu/gl/GrGpuGL.cpp (right):

https://codereview.chromium.org/15746007/diff/1005/src/gpu/gl/GrGpuGL.cpp#new...
src/gpu/gl/GrGpuGL.cpp:274: // It is believed to be slower (at least on Intel
Linux GL drivers) to readback BGRA from
I think it may be more reasonable to say "it is believed to be slower on Mesa 3D
graphics library in Linux" instead of "Intel Linux GL drivers". The decision to
make it fall back to slow path is in Mesa library(src/mesa/main/readpix.c).

[bsalomon, 2013-05-22 17:28:59]

On 2013/05/22 17:27:20, Jun Jiang wrote:
> https://codereview.chromium.org/15746007/diff/1005/src/gpu/gl/GrGpuGL.cpp
> File src/gpu/gl/GrGpuGL.cpp (right):
> 
>
https://codereview.chromium.org/15746007/diff/1005/src/gpu/gl/GrGpuGL.cpp#new...
> src/gpu/gl/GrGpuGL.cpp:274: // It is believed to be slower (at least on Intel
> Linux GL drivers) to readback BGRA from
> I think it may be more reasonable to say "it is believed to be slower on Mesa
3D
> graphics library in Linux" instead of "Intel Linux GL drivers". The decision
to
> make it fall back to slow path is in Mesa library(src/mesa/main/readpix.c).

I see Thanks for the info. I'll update the comment.

[commit-bot: I haz the power, 2013-05-24 18:30:19]

CQ is trying da patch. Follow status at
https://skia-tree-status.appspot.com/cq/bsalomon@google.com/15746007/16001

[commit-bot: I haz the power, 2013-05-24 18:52:55]

Change committed as 9280