Googling »blender 2d-filter texture« I found an old Project from 2008 which was about enabling Builder to load a Custom Uniform Texture for Use in a 2d-Filter:
The Author explains his Methos Step by Step in this Blog Post:
This Blog Post also includes a Link to PasteAll which offers what I guess is the Source Code for this Patch.
However, this was long before 2.5/2.6 and of Blender Python and the different Versions I have less than little Clue, but I guess the old Source Code might have to be modified in Order to work now? Yeah, I admit, I have not yet tried it out, Shame on me.
Also, it seems the Download Link for the old Project’s particular Build on this old GraphicAll Page does not work anymore:
I actually find it hard to believe this hasn’t made it into Trunk: Using own Textures in 2d-Filters instead of just the three for Render, Luminance and Depth? That sounds very useful indeed!
So, could this Technique be translated to a more recent Blender Version?
(I was actually trying to achieve Perlin Noise within a 2d-Filter but not only haven’t I come very far, it also seems to be, well, not the fastest Technique when using multiple Layers of Simplex Noise, so using a mere Cloud Texture would surely be a Lot faster.)