Hi all,
I'm trying to replace the fixed function texgen for a given effect by a
shader in order to remove the back projection problem. But I'm
struggling a bit to even get the texgen to work with shaders (once
that's done removing the back projection will be a cinch).
The original (fixed pipeline) code does:
_texGen= new osg::TexGen;
_texGen->setMode( osg::TexGen::OBJECT_LINEAR );
osg::StateSet *ss = geode->getOrCreateStateSet();
ss->setTextureMode(
_textureUnit, GL_TEXTURE_GEN_S, osg::StateAttribute::ON );
ss->setTextureMode(
_textureUnit, GL_TEXTURE_GEN_T, osg::StateAttribute::ON );
ss->setTextureMode(
_textureUnit, GL_TEXTURE_GEN_R, osg::StateAttribute::ON );
ss->setTextureMode(
_textureUnit, GL_TEXTURE_GEN_Q, osg::StateAttribute::ON );
ss->setTextureAttributeAndModes(
_textureUnit, _texGen.get(), osg::StateAttribute::ON );
And then later, in the cull traversal, it does:
_texGen->setPlanesFromMatrix( someMatrix );
This works well on the fixed pipeline. Now my first question when
replacing this by shaders is: I understand I need to replace the
calculation by shader code like this in the vertex shader:
gl_TexCoord[1].s = dot(gl_Vertex, gl_ObjectPlaneS[1]);
gl_TexCoord[1].t = dot(gl_Vertex, gl_ObjectPlaneT[1]);
gl_TexCoord[1].p = dot(gl_Vertex, gl_ObjectPlaneR[1]);
gl_TexCoord[1].q = dot(gl_Vertex, gl_ObjectPlaneQ[1]);
But does the setPlanesFromMatrix() fill in the gl_ObjectPlaneS/T/R/Q
builtins, or should I remove the osg::TexGen stateAttribute completely
and instead place that same matrix in some uniform and use that? i.e. in
the cull traversal:
geode->getOrCreateStateSet()->getOrCreateUniform(
"texGen", osg::Uniform::FLOAT_MAT4)->set(matrix);
and then in my shader:
uniform mat4 texGen;
//... then in main()
gl_TexCoord[1].s = dot(gl_Vertex, texGen[0]);
gl_TexCoord[1].t = dot(gl_Vertex, texGen[1]);
gl_TexCoord[1].p = dot(gl_Vertex, texGen[2]);
gl_TexCoord[1].q = dot(gl_Vertex, texGen[3]);
What is better?
Next question, is there something special I need to do in the fragment
shader to use these generated texture coordinates? Because I tried
simply doing the obvious:
vec4 col = texture2D( tex, gl_TexCoord[1].st );
and it doesn't work (I've tried using the vertex shader both ways above,
and even without any vertex shader which should revert to fixed pipeline
vertex stage...).
So I guess my second question is more important, why does the texturing
with OBJECT_LINEAR texGen not work when I just replace the fragment
shader and use the fixed function vertex processing? I would think that
would isolate the mistake to only the fragment shader...
Do I need to do something else in the fragment shader? Maybe transform
the generated texture coordinates somehow? What does the fixed pipeline
do with generated texture coords?
Thanks in advance,
J-S
--
______________________________________________________
Jean-Sebastien Guay jean-sebastien.g...@cm-labs.com
http://www.cm-labs.com/
http://whitestar02.webhop.org/
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