Am 27.11.2013 11:15, schrieb Robert Osfield:
Hi Sebastian,
Thanks for the details, still not 100% clear but clearer ;-)
The ShaderComponent class exists as an interface between
StateAttribute's and the ShaderComposer in a way that is decoupled
enough to allow fixed function pipeline style StateAttribute's to
provide a ShaderComponent to implement itself in the shader realm. It
sounds like this decoupling is a bit too one way for you needs and
that you want to be able to get the StateAttribute/ShaderAttribute
that owns the ShaderComponent, holding a parent pointer in the
ShaderComponent might be a quick fix for this but this would preclude
StateAttribute's sharing ShaderComponents which really is desirable,
the next alternative would be pass in the StateAttribute directly tot
he ShaderComposer and let it get the ShaderComponents from the
StateAttributes on demand.
Thoughts?
I don't necessarily need the provoking ShaderAttribute, but right now
there are no means to set up the binding information (attrib, fragData)
whatsoever.
I see a couple of options here.
1.) let the ShaderComposer see the provoking ShaderAttributes when
calling addShaderToProgram.
This way one could transport custom information via ShaderAttribute.
2.) Extend the ShaderAttribute so it can hold the bindings to be applied.
This would be the most fitting implementation, but would require
maintaining osg::Program alongside with ShaderAttribute if new features
are introduced. (Which I expect to happen with newer (>2) versions of
OpenGL)
3.) Add a callback mechanism which lets you inspect the Program and
shaderAttributes before it is pushed to the graph.
This seems more like a hack to me, as it is essentially 1) without the
benefit of letting the Composer decide.
So i'd really stick to version 1.) + 2.)
I'll try to explain what I want to achieve with ShaderComposer:
Imagine a multipass rendering scheme where a lot of rendering is done to
FBO.
The shaders for the passes are all like this:
#ifdef USE_TANGENT_SPACE
normal = ...
#else
normal = ...
#endif
,...
#ifdef FANCY_COLOR
color *= vec4(1,0,0,1)
#endif
So I derived the ShaderAttribute and gave it the means to inject the
#define tokens for different shader combinations.
This works very well, except for the fact, that I'm not able to set the
bindings to the osg::Program produced. So I'm stuck here.
That's why my next step was to inherit the ShaderComposer with the hope
that I somehow can access the ShaderAttribute to setup the bindings.
Option 2) would help me to bind the default bindings
Option 1) would me allow to perform the binding on my own in the
composer and possibly other things derived from the ShaderAttribute.
cheers
Sebastian
Robert.
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