Enable vertexless shading when path rendering is supported

Enable vertexless shading when path rendering is supported

Updates Skia GPU to use fragment-only shader programs when path
rendering is supported. This should include every case where path
rendering is actually used, and reduce shader state changes when it's
not. Also adds code to configure the fixed function pipeline.

[Mark Kilgard, 2013-09-10 02:13:48]

Looks fine

Comments mainly apply to further refactoring.

It really would be nice to not "double validate" the fixed-function texgen state
and the glPathTexGenNV state.  My fear is we are going to see overhead in driver
validation routines otherwise and corresponding CPU overhead.

https://codereview.chromium.org/23537028/diff/4001/src/gpu/gl/GrGpuGL.cpp
File src/gpu/gl/GrGpuGL.cpp (right):

https://codereview.chromium.org/23537028/diff/4001/src/gpu/gl/GrGpuGL.cpp#new...
src/gpu/gl/GrGpuGL.cpp:2136: fHWProjectionMatrixState.getGLMatrix<4>(glMatrix);
glMatrixLoadfEXT opportunity

https://codereview.chromium.org/23537028/diff/4001/src/gpu/gl/GrGpuGL.cpp#new...
src/gpu/gl/GrGpuGL.cpp:2152: 
It would be nice if we did *either* the fixed-function vertex validation (many
glEnable & glTexGen commands) or the single glPathTexGenNV command based on
which was actually necessary.

Can we reasonably do one or the other?

Perhaps have two routines:
1) enableTexGenFixedFunction
2) enableTexGenNVpr

And call the appropriate one?

https://codereview.chromium.org/23537028/diff/4001/src/gpu/gl/GrGpuGL.cpp#new...
src/gpu/gl/GrGpuGL.cpp:2154: 
Instead of glActiveTexture/glTexGeni/glEnable/glDisable/glTexGenfv, you can use
selector free DSA routines to do
glMultiTexGeni/glEnablei/glDisablei/glMultiTexGenfv where you install helper
routines if DSA isn't available to track the active texture.

https://codereview.chromium.org/23537028/diff/4001/src/gpu/gl/GrGpuGL.cpp#new...
src/gpu/gl/GrGpuGL.cpp:2222: 
Again, a lot of glDisable calls or glPathTexGen.

Can you do one or the other based on the true need?

[bsalomon, 2013-09-10 13:51:06]

Mostly looks good. I'd like to request adding some more documentation to
requiresVertexShader() and emitCode() in GrGLEffect explaining how to use texgen
to support vertexless shaders (to help people who are writing effects and don't
know much about Ganesh).

Also, do you think GrGLProgramDesc::Build should be updated to avoid adding
color/coverage attributes when there aren't per-vertex values and the program
could otherwise be constructed without a VS?

https://codereview.chromium.org/23537028/diff/4001/src/gpu/gl/GrGLShaderBuild...
File src/gpu/gl/GrGLShaderBuilder.cpp (right):

https://codereview.chromium.org/23537028/diff/4001/src/gpu/gl/GrGLShaderBuild...
src/gpu/gl/GrGLShaderBuilder.cpp:450: {
style nit: { up on prev line

https://codereview.chromium.org/23537028/diff/4001/src/gpu/gl/GrGpuGL.cpp
File src/gpu/gl/GrGpuGL.cpp (right):

https://codereview.chromium.org/23537028/diff/4001/src/gpu/gl/GrGpuGL.cpp#new...
src/gpu/gl/GrGpuGL.cpp:2152: 
On 2013/09/10 02:13:48, Mark Kilgard wrote:
> It would be nice if we did *either* the fixed-function vertex validation (many
> glEnable & glTexGen commands) or the single glPathTexGenNV command based on
> which was actually necessary.
> 
> Can we reasonably do one or the other?
> 
> Perhaps have two routines:
> 1) enableTexGenFixedFunction
> 2) enableTexGenNVpr
> 
> And call the appropriate one?

seems reasonable

https://codereview.chromium.org/23537028/diff/4001/src/gpu/gl/GrGpuGL.cpp#new...
src/gpu/gl/GrGpuGL.cpp:2153: setTextureUnit(unitIdx);
style nit: this->setTextureUnit(unitIdx);

(we use this-> when calling members within a class)

[Kimmo Kinnunen, 2013-09-17 09:42:40]

Just a heads-up, if the new version will be based on this one:
The coefficient array might be too small. 
Bug should manifest itself in Debug-mode gm run, spamming gl errors.

https://chromiumcodereview.appspot.com/23537028/diff/4001/src/gpu/gl/GrGpuGL.h
File src/gpu/gl/GrGpuGL.h (right):

https://chromiumcodereview.appspot.com/23537028/diff/4001/src/gpu/gl/GrGpuGL....
src/gpu/gl/GrGpuGL.h:441: GrGLfloat fCoefficients[6];
I think this should be 9 floats long.