Hi everybody,
I have the following problem: I need to develop an application that will run both on
linux and freebsd, preferably in an X environment.
This application will have to draw very simple graphic primitives (say lines) with a strong
contraint: no matter the hardware and the os, I need to be able to get back what has been
written to the videomemory and that must match per pixel what I expect having written wrote.
To be more clear, two instances of this program running on different machines with different
video card and different os must write the very same pixels to the videomemory and must
retrieve back exactly the same memory (a part from some constant conversion in the pixel format).

I think the easiest way of doing this is accessing directly the videomemory both for writing and
reading and to avoid going through any rasterizer which I can not control.
So I was guessing which is the easiest and most modern way of doing it in X.