I am creating a program where I want to rotate circles facing me(point sprites for those familiar with CG) so they look like spheres. Data I have: - coordinates of every point inside point sprite in [-1,1] € R^2 space. - center of point sprite in 3D space - point sprite normal in 3D space Best thing for me would be if I could find an equation that would test for each pair of (i,j) coordinates if they lie within a circle, rotated to a proper 3D plane determined by normal vector and center of point sprite. Is that possible? PLease bear in mind that I am not really good at this. sorry for my bad english, but I hope you understood what I meant.