Shader optimization for ovals

Shader optimization for ovals.

Previously we were setting a center point as an attribute 
across all vertices, then using that with the interpolated 
position to compute an offset. However, because the offset 
computation is linear, we can just set the appropriate offset 
at the vertices and let the rasterizer interpolate it for us. 

Committed: http://code.google.com/p/skia/source/detail?r=8613

[robertphillips, 2013-04-10 23:18:39]

lgtm - could you paste the performance numbers here?

https://codereview.chromium.org/14093002/diff/2001/src/gpu/GrOvalRenderer.cpp
File src/gpu/GrOvalRenderer.cpp (right):

https://codereview.chromium.org/14093002/diff/2001/src/gpu/GrOvalRenderer.cpp...
src/gpu/GrOvalRenderer.cpp:539: 
For the rect edge passing the bounds actually slowed things down.

[jvanverth1, 2013-04-11 14:16:45]

Here are the perf numbers on Mac OS. I'm not sure why ovals_1 and ovals_3 didn't
show any improvement -- I guess they're just too fast already.

     draw_stroke_oval_bevel GPU            1.00       1.00      +0.00    +0.0% 
     draw_stroke_oval_miter GPU            1.01       1.01      +0.00    +0.0% 
     draw_stroke_oval_round GPU            1.00       1.00      +0.00    +0.0% 
gradient_radial1_clamp_oval GPU            0.00       0.00      +0.00    +0.0% 
                    ovals_1 GPU            1.00       1.00      +0.00    +0.0% 
                    ovals_3 GPU            1.00       1.00      +0.00    +0.0% 
       path_fill_big_circle GPU            2.00       2.00      +0.00    +0.0% 
         path_fill_big_oval GPU            1.00       1.00      +0.00    +0.0% 
     path_stroke_big_circle GPU            2.00       2.00      +0.00    +0.0% 
       path_stroke_big_oval GPU            1.00       1.00      +0.00    +0.0% 
     path_fill_small_circle GPU            2.03       2.00      +0.03    +1.5% 
               circles_fill GPU           16.00      15.73      +0.27    +1.7% 
   path_stroke_small_circle GPU            2.07       2.00      +0.07    +3.4% 
             circles_stroke GPU           21.98      21.00      +0.98    +4.5% 
       path_fill_small_oval GPU            2.10       2.00      +0.10    +4.8% 
     path_stroke_small_oval GPU            2.56       2.06      +0.50   +19.5% 


On 2013/04/10 23:18:39, robertphillips wrote:
> lgtm - could you paste the performance numbers here?
> 
> https://codereview.chromium.org/14093002/diff/2001/src/gpu/GrOvalRenderer.cpp
> File src/gpu/GrOvalRenderer.cpp (right):
> 
>
https://codereview.chromium.org/14093002/diff/2001/src/gpu/GrOvalRenderer.cpp...
> src/gpu/GrOvalRenderer.cpp:539: 
> For the rect edge passing the bounds actually slowed things down.

[commit-bot: I haz the power, 2013-04-11 14:26:00]

CQ is trying da patch. Follow status at
https://skia-tree-status.appspot.com/cq/jvanverth@google.com/14093002/2001

[commit-bot: I haz the power, 2013-04-11 15:05:39]

Change committed as 8613