J-S (and others),
You could look at doing this is the same way the depth partition node does
it, which is what I do:
I use a class based on an OSG camera with an overriden traverse method, that
forces the projection matrix to a particular z near and z far. Oh, and the
camera has setComputeNearFarMode(osg::CullSettings::DO_NOT_COMPUTE_NEAR_FAR)
in its constructor. The skydome is then a child of this camera.
You then set the z near and z far to be whatever you want (i.e. enveloping
your skydome radius). I typically have a skydome with a radius of 1
void CExtentsCamera::traverse(osg::NodeVisitor &nv)
{
// If the scene hasn't been defined (i.e. we have no children at all)
then don't do anything
if(_children.size() == 0) return;
// If the visitor is not a cull visitor, then we are not interested in
intercepting it, so pass it directly onto the scene.
osgUtil::CullVisitor* cv = dynamic_cast<osgUtil::CullVisitor*>(&nv);
if(!cv)
{
Camera::traverse(nv);
return;
}
// Get a reference to the Cull Visitor's projection matrix
osg::Matrix* projection = cv->getProjectionMatrix();
// NB : This might be possible to simplify and hence optimise (haven't
yet checked)
double a = (*projection)(2,2);
double b = (*projection)(3,2);
double c = (*projection)(2,3);
double d = (*projection)(3,3);
double trans_near = (-_zNear*a + b) / (-_zNear*c + d);
double trans_far = ( -_zFar*a + b) / ( -_zFar*c + d);
double ratio = fabs(2.0/(trans_near - trans_far));
double center = -0.5*(trans_near + trans_far);
// Set the projection matrix
projection->postMult(osg::Matrixd( 1.0, 0.0, 0.0, 0.0,
0.0, 1.0, 0.0, 0.0,
0.0, 0.0, ratio, 0.0,
0.0, 0.0, center*ratio, 1.0));
Camera::traverse(nv);
}
Probably a better way of doing it, but it works fine for me.
I also do this on the "camera"'s stateset
{
osg::Depth* depth = new osg::Depth;
depth->setFunction(osg::Depth::LEQUAL);
depth->setRange(1.0,1.0);
stateSet->setAttributeAndModes(depth,osg::StateAttribute::ON );
}
so that you can render the sky last, and any expensive pixel shaders don't
get unnecessarily run.
Hope that helps,
David
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