Thread: GLX/X11 Changing the rendering resolution

I have made a simple application that creates a window with an OpenGL 4.2 context and takes user input.

I have implemented making the window go fullscreen with XRandR and can change the display resolution.

I would like to change this so that I don't have to set the displays resolution and only the window/contexts so that it renders at a lower resolution but the display stays at its default.

How could I implement this? Which extensions provide this or can I do this with XRandR and just manipulating the window rather than the root window(dektop)?

Thanks.

I think this answer is too obvious, but since nobody else responded, here goes.

Originally Posted by Coffee_and_Code

I would like to [render] at a lower resolution [than the] display[.]

Create an offscreen surface with the same pixel format as your window, and render to that surface instead of directly to your window.

Whenever the window needs updating, copy the surface contents to the window (scaling the surface to fill the window).

If you use two surfaces, you can render to one while drawing the other to the window; this is a classic example of double buffering.

Originally Posted by Coffee_and_Code

I would like to change this so that I don't have to set the displays resolution and only the window/contexts so that it renders at a lower resolution but the display stays at its default.

I would recommend against this.

Users generally expect all of the pixels on their screen to be taken advantage of, forfeiting resolution (especially without the user's consent) will be unfriendly.

Besides, unless your rendering resolution is a clear multiple of your screen's, it will be ugly unless you antialias.

Alternatively, consider providing the option to render to a decorated window where the user may tweak the dimensions to their heart's content.