I have a projector, which doesn't come with horizontal keystone correction builtin, only vertical correction. I've seen that it is possible to do it with xrandr, using the --transform parameter, but needs matrix coordinates and I'm lost. There's a GUI, ARandR, but doesn't support transformations.
I've also checked MapMap project, but seems a v4l2 virtual video device stream fed by ffmpeg's x11grab isn't well recognized to use it as source.
Do you know any other alternative to transform the screen (free style, like a trapezoid)?
Is there something similar on Wayland display server?