Re: [osg-users] If I set a vertex color using floats and access the vertex color in a shader, is there a loss of precision?

[Christian Buchner]

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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