Add option to add precision to varyings in shader

Add option to add precision to varyings in shader

Also use highp varying on bezier cubics to fix numerical issues for n10 and n4.

BUG=skia:2860
Committed: https://skia.googlesource.com/skia/+/6db9128efb3b720252b6094dc2640796b66456aa

[egdaniel, 2014-09-02 14:30:28]

egdaniel@google.com changed reviewers:
+ bsalomon@google.com

[egdaniel, 2014-09-02 14:30:29]

This change fixes the n10 issue where cubic bezier curves didn't go all the way
to their end points. For the n4 it removes numerical issues causing large
blotches of blurring type effects that would show up on cubics.

https://codereview.chromium.org/522303004/diff/1/src/gpu/gl/builders/GrGLProg...
File src/gpu/gl/builders/GrGLProgramBuilder.cpp (left):

https://codereview.chromium.org/522303004/diff/1/src/gpu/gl/builders/GrGLProg...
src/gpu/gl/builders/GrGLProgramBuilder.cpp:347: fVS.addVarying(type, name,
vsOutName);
should the precision be passed down to the VS as well? for cubic fixes highp is
only needed in the fragment varying

[bsalomon, 2014-09-02 14:46:59]

lgtm, w/ suggestion for param name change.

https://codereview.chromium.org/522303004/diff/1/src/gpu/gl/builders/GrGLProg...
File src/gpu/gl/builders/GrGLProgramBuilder.cpp (left):

https://codereview.chromium.org/522303004/diff/1/src/gpu/gl/builders/GrGLProg...
src/gpu/gl/builders/GrGLProgramBuilder.cpp:347: fVS.addVarying(type, name,
vsOutName);
On 2014/09/02 14:30:29, egdaniel wrote:
> should the precision be passed down to the VS as well? for cubic fixes highp
is
> only needed in the fragment varying

The spec doesn't require them to match. The default for the VS is highp already.
Why don't we just specify the FS precision and change the param name to
fsPrecision?

[egdaniel, 2014-09-02 14:55:03]

The CQ bit was checked by egdaniel@google.com

[commit-bot: I haz the power, 2014-09-02 14:55:26]

CQ is trying da patch. Follow status at
 https://skia-tree-status.appspot.com/cq/egdaniel@google.com/522303004/20001

[commit-bot: I haz the power, 2014-09-02 15:02:52]

Committed patchset #2 (id:20001) as 6db9128efb3b720252b6094dc2640796b66456aa