Use GL_ALPHA instead of GL_RED to create texture in mesa if no GL_ARB_texture_rg extension

Use GL_ALPHA instead of GL_RED to create texture in mesa if it no GL_ARB_texture_rg extension. 

bsalomon submitted another patch related to this, see: https://codereview.chromium.org/16955005/

[yunchao, 2013-06-04 08:32:26]

Use GL_ALPHA instead of GL_RED to create texture in mesa if it doesn't have
GL_ARB_texture_rg extension, although GL_ARB_texture_rg(who contain GL_R8,
GL_RED, etc) should be supported when GLVersion is above 3.0.

[yunchao, 2013-06-13 02:01:39]

On 2013/06/04 08:32:26, yunchao wrote:
> Use GL_ALPHA instead of GL_RED to create texture in mesa if it doesn't have
> GL_ARB_texture_rg extension, although GL_ARB_texture_rg(who contain GL_R8,
> GL_RED, etc) should be supported when GLVersion is above 3.0.

bsalomon and robertphillips, any comments about this?

[bsalomon, 2013-06-13 13:09:47]

On 2013/06/13 02:01:39, yunchao wrote:
> On 2013/06/04 08:32:26, yunchao wrote:
> > Use GL_ALPHA instead of GL_RED to create texture in mesa if it doesn't have
> > GL_ARB_texture_rg extension, although GL_ARB_texture_rg(who contain GL_R8,
> > GL_RED, etc) should be supported when GLVersion is above 3.0.
> 
> bsalomon and robertphillips, any comments about this?

yunchao, can you check whether this CL works:

https://codereview.chromium.org/16955005/

I don't have a system handy to test with.

I wanted to generalize the detection of mesa since we may find other
differences. (We should do the same for ANGLE on the windows side to remove some
of our compile time macros).

[yunchao, 2013-06-14 03:47:43]

On 2013/06/13 13:09:47, bsalomon wrote:
> On 2013/06/13 02:01:39, yunchao wrote:
> > On 2013/06/04 08:32:26, yunchao wrote:
> > > Use GL_ALPHA instead of GL_RED to create texture in mesa if it doesn't
have
> > > GL_ARB_texture_rg extension, although GL_ARB_texture_rg(who contain GL_R8,
> > > GL_RED, etc) should be supported when GLVersion is above 3.0.
> > 
> > bsalomon and robertphillips, any comments about this?
> 
> yunchao, can you check whether this CL works:
> 
> https://codereview.chromium.org/16955005/
> 
> I don't have a system handy to test with.
> 
> I wanted to generalize the detection of mesa since we may find other
> differences. (We should do the same for ANGLE on the windows side to remove
some
> of our compile time macros).

Hi, bsalomon, the CL works. I have tested on my desktop with mesa.