Hi, Mike, Robert, folks,
Thanks for the help from this list, I've decided to use a
uniform to solve the problem of switching lighting mode between
fragments. My idea is to add the program and a LightingOn uniform
to the stateset of the root node of the scenegraph, and set its
value to 0 wherever the stateset of a node has GL_LIGHTING off,
and to 1 wherever GL_LIGHTING is on. However, on a closer
thought, here comes a problem. For the GL_LIGHTING mode in the
stateset of a node, I can set it to whatever value and it won't
affect that in the stateset of a different node, and individual
glEnable(GL_LIGHTING) and glDisable(GL_LIGHTING) will be called
during the draw stage. But if I'm sharing a uniform, is it that
during the draw stage only one call to glUniform() for that
uniform will take place, and its value will be that of the last
call to Uniform::Set() before the draw stage? How do I make
multiple glUniform() calls to the same uniform take place during
the draw stage alongside glEnable/glDisable(GL_LIGHTING)? I
don't think it's correct to create a separate osg::Uniform for
each node, which in the minimum will induce multiple
glGetUniformLocation() calls? Can I use a callback? A draw
callback?
A second approach is to create two sets of shaders and two
programs, one for non lit fragments, and another for lit fragments.
Then I just set the appropriate program to the stateset of each
node in the scenegraph. Will this work? I imagine there may be
thousands of glUseProgram() calls during each draw. I don't know
how big an impact it will be on the performance.
Thanks!
Yefei
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