Hello I would like to implement ComputeSphereVisibility. The sting game is completely black because of this stubbed function. Here is my idea to implement it. Am I in the good way, or it is completely a bad idea? With GetViewport, I retrieve the viewport matrix V, and with GetTransform, I retrieve projection P and world W matrices ofn the device. I multiply the three matrices in a matrice M: M=VPW If M is singular, function returns with a failing message Otherwise, with the matrix M I retrieve the planes of the frustum view (that's a little bit of math, but quite easy) Then for each sphere, Let Visibility=0 for each plane of the frustum view Let I be the intersection of the orthogonal projection of the center sphere on the plane. If I is in the frustum view, then I have the visibility.So Visibility=Visibility|(flag for the visibility of the chosen plane) Once I did it for the 6 plane, I have the visibility of the sphere. Is it a good point of start? David