So you want to draw the whole face again just with adjusted texture coordinates for the decal? I suppose that?¢_Ts one to avoid clipping it, but unless all you?¢_Tre faces are really small you?¢_Tll burn a lot of fillrate on totally transparent fragments (might seem not much now, but what if a face close to the camera has tens of bullet marks). But then I don?¢_Tt get what you want with the axis. And why you?¢_Td mess with texture matrix at all, since you?¢_Td still need to fill in texture coordinates. I still suggest you do it the way I described above and mess with decal?¢_Ts vertex rather than texture coordinates.