gl.render offset(offaxis) message? Perspective correction...

What is the message and way to use it for renderind an offset (offaxis) gl view? (camera is not moving!!!)
after web search I thought perhaps it's : glTranslated. I also remenber (years ago that gl had such function)

I'll use it to simulate the offaxis projection viewpoint of video beamer. Generally 50/70% down the central vertical axis.

Example:I use a 1024x1536 window of a render context, and display only the half upper part to simulate a video beamer(w. 50% offset).
It would be better if i could work with a 1024x768 window of an offsetted render

thanks

Spat