For using generic vertex attributes, you could refer to these
(partial) code snippets.
I pass some custom texture coordinates as a float2 attribute with each vertex.
Can be easily changed to float4, if needed.
osg::Geometry *meshGeom;
// so we use a float attribute array instead
osg::Vec2Array* xypositions = new osg::Vec2Array();
xypositions->setName("xypos");
// for loop over all vertices, adds texture coordinates
for (...)
xypositions->push_back(osg::Vec2(xcoord, ycoord));
// only use binding to attribute index 6 or 7 as these are not used by OSG.
meshGeom->setVertexAttribArray(6, xypositions);
meshGeom->setVertexAttribNormalize(6, false);
meshGeom->setVertexAttribBinding(6, osg::Geometry::BIND_PER_VERTEX);
osg::Program* program = new osg::Program;
program->setName( "mesh" );
program->addBindAttribLocation("xypos", 6);
// and here is how I access the custom attribute in a vertex shader.
// I perform a gaussian interpolation over sample values contained in
a 2D texture,
// and use that to displace a 3D mesh vertically.
static const char *VertexShader = {
"#version 120\n"
"uniform float K;\n"
"uniform float N;\n"
"uniform sampler2D datatex;\n"
"in vec2 xypos;\n"
"void main(void)\n"
"{\n"
" // gaussian 3x3 filter kernel;\n"
" float foo = 41.0 * texture2D(datatex, xypos).x\n"
" + 26.0 * texture2D(datatex, xypos+vec2(+K , 0 )).x\n"
" + 26.0 * texture2D(datatex, xypos+vec2(-K , 0 )).x\n"
" + 26.0 * texture2D(datatex, xypos+vec2( 0 ,+N )).x\n"
" + 26.0 * texture2D(datatex, xypos+vec2( 0 ,-N )).x\n"
" + 16.0 * texture2D(datatex, xypos+vec2(-K ,+N )).x\n"
" + 16.0 * texture2D(datatex, xypos+vec2(-K ,-N )).x\n"
" + 16.0 * texture2D(datatex, xypos+vec2(+K ,+N )).x\n"
" + 16.0 * texture2D(datatex, xypos+vec2(+K
,-N )).x;\n"
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