I am currently running a GUI application via Weston, all this running on QEMU. Everything is fine but, for reason I cannot disclose, I would like to be able to control the contrast of the image displayed.

For example have a slider to adjust the contrast in some kind of setting screen.

Is there any way to do that? Via Weston or via an API targeting directly the virtio-gpu?

I would really appreciate if anyone could give me a hint on this.

Thank you very much!