Looping datas in GPU ? + NV_point_sprites orientation

Hello everyone,

this may sound as a strange question, but
I need to use some informations computed
in a pixel shader in the vertex shader (at the next time step). First I thought that:

  • I could render those informations in a tetxture, but it seems that it is not possible to access texture data in a vertex shader (maybe this feature will be included in the next versions of vertex shaders ?),
  • maybe I can store those informations in the graphic card memory, but how to achieve this still remains a big dark area in my knowledges of OpenGl.

The obvious solution would be to perform
a readback of some buffer, and put the information as a per-vertex data in the entry of the pipeline, but I fear that this readback could cause performance problems…

If anyone has an idea about this (I hope my question is clearly enough formulated, otherwise I’ll try to explain it differently)

My second question is about point sprites, it is possible to rotate those sprites ? The problem occurs when the texture is orientated…

Thanks for all your answers, maybe some of this questions have already been answered in this forum but I didn’t get the info…