render without displaying window and resize image

OpenGL OpenGL: Basic Coding
1

Hi all,
i am an newbe to OpenGl. I would like to use OpenGL to render a scene. The scene hasn’t to be shown in a window, so no visualization of the scene is needed.
The rendering should be triggered from the program and not run in an whil(true) loop.

I would like to render a szene with OpenGL,
load the picture from the buffer with glReadPixels,
resize the display to a new size. render a new scene,
load the new picture with new size from the buffer with glReadPixels,
etc, etc

Here my questions:
How can I use OpenGL without a open window?
How can I set/change the displaysize in the program for the next szene?

Many thanks for reading so far, hope someone has an idea.

Best regards,
Huppifluppi

2

Huppi
Are you trying to say that you want your scene to be fullscreen or that you want to use OpenGL to render a graphics scene but not create a window to display it?