On Mon, 5 Mar 2012 19:41:14 -0800 (PST), Benoit Jacob <bja...@mozilla.com> wrote: > > For a bunch of it, apps don't use it so nobody would notice. > > glBitmap and glDrawPixels are reasonably popular, though. You should > > be > > able to build those with shaders, though. You can see partial > > implementations for these in on top of fixed function in Mesa as > > src/mesa/drivers/common/meta.c (contributions welcome, particularly > > in > > the form of GLSL-based implementations of them!) > > Thanks for the pointer but that (a GLES2-based implementation) is > precisely what we're looking for :-)
I was mostly thinking in terms of how to set up state, which I find to be the hard part of writing the metaops -- converting the ff fragment shading to GLSL should be pretty easy, since if it can be written in fixed function it's usually trivial. I want to do the GLSL conversions of them some day, since it would be less overhead for us, but it's low on the task list. > Before we'd start caring about glBitmap and glDrawPixels, we have more > fundamental things to implement: > - glBegin ... glVertex ... glEnd The src/mesa/vbo module handles this (the driver ends up with a callback to draw a number of primitives with a particular collection of VBOs, using the state that the driver had already been told about) and that plus src/mesa/main/dlist.c handle display lists. That's actually a huge component, and probably justifies making a Mesa driver out of this thing. > - glShadeModel(GL_FLAT) (this one seems really hard to do with OpenGL > ES2, a real capability regression from OpenGL [ES] 1 it seems!) Ouch. I keep trying to come up with workarounds for this, but I'm ending up with things that use even later GL functionality. Rewrite your VBOs, I guess, but that gets really awful in the case of vertex shading. > - the lighting model (glLight, glMaterial) The code we have for doing this in src/mesa/main/ff_fragment_shader.cpp and src/mesa/main/ffvertex_prog.c generate IRs, not GLSL source. This sounds like another argument for making a Mesa driver and glueing Aras's stuff onto the backend, since that consumes our IR as the input. (You may note that ffvertex_prog.c doesn't generate GLSL IR, it generates Mesa IR. That's on the list of tasks for changing this quarter)
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