   How do I access pixels in glTexImage2D for collision detection purposes?
  Folks, let's say that I map a texture like so:    glBindTexture(GL_TEXTURE_2D, texture[5]);glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST );    glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST ); glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, alphaSurface->w, alphaSurface->h, 0, texture_format, GL_UNSIGNED_BYTE, alphaSurface->pixels);    SDL_FreeSurface(alphaSurface);How do I later access the pixels passed into the glTexImage2D here for purposes of doing a per-pixel collision detection?  I believe I can do the per pixel detection if I can get the alpha channels in that texture.   
  Check out this;  Why not just keep a copy of the origional pixel data stored in alphaSurface?Instead of sending to the GPU and then asking for it back. Which isn't exactly the most efficient method possible.   ;  You're right.  And in any case, I have discovered that there are better ways to do what I want to do, which is to test an irregular shape against other irregular shapes.  It will take some hand-crafted placements of sub-bounding-circles and I will have to deal with the rotations and translations as I move my projectiles around, but it should be easier than per pixel.  Thanks for the input.   