Add support for half float alpha textures.

Add support for half float alpha textures.

This allows us to create distance field textures with better precision,
which may help text quality.

BUG=skia:3103
Committed: https://skia.googlesource.com/skia/+/28f9c606e4c8e61015e864219c4bc83a3fdb4a86

[jvanverth1, 2014-12-04 19:47:55]

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

[bsalomon, 2014-12-04 20:36:41]

https://codereview.chromium.org/762923003/diff/20001/include/gpu/GrTypes.h
File include/gpu/GrTypes.h (right):

https://codereview.chromium.org/762923003/diff/20001/include/gpu/GrTypes.h#ne...
include/gpu/GrTypes.h:413: static inline bool
GrPixelConfigIsAlphaOnly(GrPixelConfig config) {
update this?

https://codereview.chromium.org/762923003/diff/20001/src/gpu/gl/GrGLCaps.cpp
File src/gpu/gl/GrGLCaps.cpp (right):

https://codereview.chromium.org/762923003/diff/20001/src/gpu/gl/GrGLCaps.cpp#...
src/gpu/gl/GrGLCaps.cpp:474: // TODO: special check for R16F on ES?
wondering why this and rgba_float don't enable MSAA?

If we're just deciding to punt on it then maybe mention that here?

https://codereview.chromium.org/762923003/diff/20001/src/gpu/gl/GrGLCaps.cpp#...
src/gpu/gl/GrGLCaps.cpp:614: fConfigTextureSupport[kAlpha_half_GrPixelConfig] =
hasFPTextures;
I think in the OES case there is a separate extension GL_OES_texture_half_float
that you have to look for (which can be present w/ or w/o GL_OES_texture_float).

[jvanverth1, 2014-12-05 20:16:37]

Addressed the issues below. I also found out that HALF_FLOAT has different
values in OGL and OGL_ES, so fixed that. I also check for Red support before
enabling Alpha_half on mobile.

https://codereview.chromium.org/762923003/diff/20001/include/gpu/GrTypes.h
File include/gpu/GrTypes.h (right):

https://codereview.chromium.org/762923003/diff/20001/include/gpu/GrTypes.h#ne...
include/gpu/GrTypes.h:413: static inline bool
GrPixelConfigIsAlphaOnly(GrPixelConfig config) {
On 2014/12/04 20:36:41, bsalomon wrote:
> update this?

Done.

https://codereview.chromium.org/762923003/diff/20001/src/gpu/gl/GrGLCaps.cpp
File src/gpu/gl/GrGLCaps.cpp (right):

https://codereview.chromium.org/762923003/diff/20001/src/gpu/gl/GrGLCaps.cpp#...
src/gpu/gl/GrGLCaps.cpp:474: // TODO: special check for R16F on ES?
On 2014/12/04 20:36:41, bsalomon wrote:
> wondering why this and rgba_float don't enable MSAA?
> 
> If we're just deciding to punt on it then maybe mention that here?

Added MSAA support for desktop, punting on mobile.

https://codereview.chromium.org/762923003/diff/20001/src/gpu/gl/GrGLCaps.cpp#...
src/gpu/gl/GrGLCaps.cpp:614: fConfigTextureSupport[kAlpha_half_GrPixelConfig] =
hasFPTextures;
On 2014/12/04 20:36:41, bsalomon wrote:
> I think in the OES case there is a separate extension
GL_OES_texture_half_float
> that you have to look for (which can be present w/ or w/o
GL_OES_texture_float).

Done.

[bsalomon, 2014-12-05 20:21:27]

https://codereview.chromium.org/762923003/diff/40001/src/gpu/gl/GrGLCaps.cpp
File src/gpu/gl/GrGLCaps.cpp (right):

https://codereview.chromium.org/762923003/diff/40001/src/gpu/gl/GrGLCaps.cpp#...
src/gpu/gl/GrGLCaps.cpp:485:
fConfigRenderSupport[kAlpha_half_GrPixelConfig][kNo_MSAA] = fTextureRedSupport;
is fTextureREdSupport not already checked in isConfigTexturable()?

https://codereview.chromium.org/762923003/diff/40001/src/gpu/gl/GrGLCaps.cpp#...
src/gpu/gl/GrGLCaps.cpp:638: fConfigTextureSupport[kAlpha_half_GrPixelConfig] =
hasHalfFPTextures;
hasHPT && fTextureRedSupport?

https://codereview.chromium.org/762923003/diff/40001/src/gpu/gl/GrGLDefines.h
File src/gpu/gl/GrGLDefines.h (right):

https://codereview.chromium.org/762923003/diff/40001/src/gpu/gl/GrGLDefines.h...
src/gpu/gl/GrGLDefines.h:307: #define GR_GL_HALF_FLOAT_OES                
0x8D61
ARGGHHHHH!

[jvanverth1, 2014-12-05 20:31:41]

https://codereview.chromium.org/762923003/diff/40001/src/gpu/gl/GrGLCaps.cpp
File src/gpu/gl/GrGLCaps.cpp (right):

https://codereview.chromium.org/762923003/diff/40001/src/gpu/gl/GrGLCaps.cpp#...
src/gpu/gl/GrGLCaps.cpp:485:
fConfigRenderSupport[kAlpha_half_GrPixelConfig][kNo_MSAA] = fTextureRedSupport;
On 2014/12/05 20:21:27, bsalomon wrote:
> is fTextureREdSupport not already checked in isConfigTexturable()?

Whoop, right. I was thinking isConfigTexturable was checking half float support
in general.

https://codereview.chromium.org/762923003/diff/40001/src/gpu/gl/GrGLCaps.cpp#...
src/gpu/gl/GrGLCaps.cpp:638: fConfigTextureSupport[kAlpha_half_GrPixelConfig] =
hasHalfFPTextures;
On 2014/12/05 20:21:27, bsalomon wrote:
> hasHPT && fTextureRedSupport?

Done.

https://codereview.chromium.org/762923003/diff/40001/src/gpu/gl/GrGLDefines.h
File src/gpu/gl/GrGLDefines.h (right):

https://codereview.chromium.org/762923003/diff/40001/src/gpu/gl/GrGLDefines.h...
src/gpu/gl/GrGLDefines.h:307: #define GR_GL_HALF_FLOAT_OES                
0x8D61
On 2014/12/05 20:21:27, bsalomon wrote:
> ARGGHHHHH!

Yeah.

This is why my initial tests didn't work -- I was using the OES value on
desktop.

[bsalomon, 2014-12-05 20:44:41]

lgtm

[jvanverth1, 2014-12-05 20:56:43]

The CQ bit was checked by jvanverth@google.com

[commit-bot: I haz the power, 2014-12-05 20:57:29]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/762923003/60001

[commit-bot: I haz the power, 2014-12-05 21:06:40]

Committed patchset #4 (id:60001) as
https://skia.googlesource.com/skia/+/28f9c606e4c8e61015e864219c4bc83a3fdb4a86