Won't that change on every frame/pixel ?
Yes it will.
There is no easy solution available in iStripper other than one based on selecting a random texture from a folder of textures.
What is really needed for this sort of things is a "compute shader". The GLSL graphics pipe line comprises roughly the following series of "shader" stages executed in the following order
Initialise
Compute
Geometry
Vertex
Fragment
where each acts on the output of the previous stage and handles it in increasing detail.
The .scn file is handled at the Initialise and Compute stages (Animate clauses need actions after the initialise stage) providing data that is then used to compute the scene's geometry. The scene is then divided into a set of triangles each with three vertexes and each triangle divided into pixels each of which is handled as a fragment.
iStripper allows us to provide our own shaders for the vertex and fragment stages, but only allows us to provide limited data inputs to the compute and geometry stages.
It would be nice if iStripper provided more standard data via uniform variables - such as the date, time of day and mouse position etc. For example I have a set of clocks I would like to use as screen savers and it would be nice if they showed the correct time.
Another thing I would really like to see (but which I doubt will ever be implemented) is to be able to do simple calculations in the .scn file - with these calculations having access to such data as the date and time and to a few functions like sin(), cos() and rand().
ADDENDUM:
I suppose you could use one of Z22's feedback buffers to cache a calculation. A shader could be used to generate a copy of this "cache" for use next time or to generate its value if that old value was 0.0. But this would be far from a simple solution.