Horde3D

void h3dutProject(H3DNode cameraNode, Vec3f world, float *x, float *y) {
   Matrix4f projMat;
   h3dGetCameraProjMat(cameraNode, projMat.x);

   const float *camTrans;
   h3dGetNodeTransMats( cameraNode, 0x0, &camTrans );      
   Matrix4f viewMat( camTrans );
   viewMat = viewMat.inverted();

   Matrix4f viewProjMat = projMat * viewMat;
   Vec3f screen = viewProjMat * world;
   if (x) {
      *x = screen.x / screen.z;
   }
   if (y) {
      *y = screen.y / screen.z;
   }
}