In an ideal world, vertex attributes would work more like uniforms.
You'd specify a shader variable name along with your array, and OSG
would determine the slot number to use in the call to OpenGL.
For whatever reason, it wasn't implemented that way, and instead you
need to specify the slot number yourself. To complicate things,
apparently OSG has reserved certain slot numbers for itself in order to
support the old GL1/2 special case vertex attributes (like
setVertexArray, setNormalArray, setColorArray, etc).
Digging through the code to divine exactly how you should deal with this
at the application level is somewhat difficult. A good place to start
would be grepping the source for the GL calls related to vertex attributes.
Paul Martz
Skew Matrix Software LLC
_http://www.skew-matrix.com_ <http://www.skew-matrix.com/>
+1 303 859 9466
Andrew Holland wrote:
Hi,
I tried using a different attribute index from 0, and the colours are now
showing up. I had come across the link earlier that you posted, but didn't
realise that was how OpenGL worked (I tested it out in an OpenGL app and got
the same problem as in my OSG app, with the slightly deformed mesh and no
colours).
So if I use custom attributes and no built in ones, then I shouldn't have this
problem of overwriting existing attributes, which I also tested in the OpenGL
app, and it allowed me to use 0 for a vertex attrib, and 1 for a colour attrib.
So that's what I want to do now in my OSG app. But I cannot get it to work, it
just renders nothing. I have tried different attribute values (from '0 and 1',
'10 and 11', to '0 and 11'), but to no avail.
I've posted what I believe is the relevant code, maybe I didn't set the vertex
data right in the geometry. The code here currently renders nothing.
Code:
GLuint vertLoc = 0;
GLuint colLoc = 1;
//
osg::Geode* pyramidGeode = new osg::Geode();
root->addChild(pyramidGeode);
//geometry
osg::Geometry* pyramidGeometry = new osg::Geometry();
pyramidGeode->addDrawable(pyramidGeometry);
//vertices
osg::Vec3Array* pyramidVertices = new osg::Vec3Array;
for(int i=0;i<model->verticesNum;i++) {
float x = model->positions[i*3];
float y = model->positions[i*3+1];
float z = model->positions[i*3+2];
pyramidVertices->push_back(osg::Vec3(x,y,z));
}
//pyramidGeometry->setVertexArray(pyramidVertices);
program->addBindAttribLocation("a_vertex", vertLoc);
pyramidGeometry->setVertexAttribArray(vertLoc,pyramidVertices);
pyramidGeometry->setVertexAttribBinding(vertLoc,
osg::Geometry::BIND_PER_VERTEX);
}
//colours
osg::Vec4Array* colors = new osg::Vec4Array;
for(int i=0;i<model->verticesNum;i++) {
float r = model->cols[i*4];
float g = model->cols[i*4+1];
float b = model->cols[i*4+2];
float a = model->cols[i*4+3];
colors->push_back(osg::Vec4(r,g,b,a));
}
program->addBindAttribLocation("a_col", colLoc);
pyramidGeometry->setVertexAttribArray(colLoc, colors);
pyramidGeometry->setVertexAttribBinding(colLoc, osg::Geometry::BIND_PER_VERTEX);
}
//indices
osg::DrawElementsUInt* pyramidBase = new
osg::DrawElementsUInt(osg::PrimitiveSet::TRIANGLES,model->indicesNum,model->indices,
0);
pyramidGeometry->addPrimitiveSet(pyramidBase);
and the shaders
Code:
//vertex shader
attribute vec3 a_vertex;
attribute vec4 a_col;
varying vec4 col;
void main() {
col = a_col;
//gl_Position = gl_ModelViewProjectionMatrix * gl_Vertex
gl_Position = gl_ModelViewProjectionMatrix * vec4(a_vertex, 1.0);
}
//fragment shader
varying vec4 col;
void main() {
gl_FragColor =col;
}
Thanks.
------------------
Read this topic online here:
http://forum.openscenegraph.org/viewtopic.php?p=22482#22482
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