Jit value (0-1) to pixel (1024 to 768)

Hello all.

I would like to create a convertor from gl values to pixel values

For example, in gl world, the position should be in -1 1 format.
I would like to convert it in pixel, so the center of picture would be 512- 384 for a 1024*768 screen.
And I want to know it for every point (Keystone (ABCD), center,...

To complicate a litle bit, i would like to do this dynamicaly, whatever is the screen size (with jit.displays)

So... i want to know where i'am !

If you can help me to find myself, thanks!