View Full Version : Bump Mapping - tangent space question

03-18-2006, 11:08 AM
Generally speaking, is it better to compute rotations of vectors into tangent space with a vertex shader or with the cpu? ( Assuming that lighting positions can move and specular & other components will be computed in the fragment shader )
I know the questions really depends, but what would you rather do (or which do you use now? )

03-18-2006, 12:52 PM
In most situations the GPU calculation is better. If you do it on GPU you will have following benefits:

The power of GPU vertex shaders is mostly unused so offloading some work from CPU which can then be used for physics or better AI is usefull. All geometry can be static and stored on the card which reduces bus bandwith necessary for rendering. It allows you to do skinning of characters on the GPU. Single geometry can be shared by several instances of mesh (think army of soldiers or bar room with many chairs) which can significantly reduce memory requirements. On some HW you can easily use various packed formats to store normal values so this also reduces memory requirements.