I’m trying to implement an iterative reconstruction algorithm on a graphics card. To represent the volume I choose 2 stacks of 2d Textures. Which of the stacks I choose depends of the geometry of the currently processed projection image. My Problem now is that after the hole process one of the stacks is updated with glCopyTexImage2D and the which is perpendicular to the other must be updated with glCopyTexSubImage2D about 256 times and from 256 textures. So it is very very slow. Is there some nice way to get out of a texture stack a new texture stack where the slices are perpendicular??