Immediately after enabling OpenGL on Pi3 and rebooting, all standard HDMI options that enables us to change screen resolution and overscan no longer worked.
A quick search for a documented way to change screen resolution and set overscan with OpenGL enabled on Pi3 didn't turned out anything.
I was wondering if anyone knows a way of changing resolution and set overscan offsets with OpenGL enabled.
Thank you.
Note: I cannot create the OpenGL tag.
The open source driver has no access to config.txt, so it doesn't see the proprietary driver's options. However, you now have access to all the standard resolution configuration tools for Linux. So you can see the modes your monitor reports support for from the command line in X with:
xrandr
and do one-shot resolution setting at runtime with:
xrandr --output HDMI-1 --mode 1024x768
Additionally, normal desktop tools for configuring resolution will also work. For example, if you use GNOME's display settings tool, it does clever things like notice which monitor you're plugged into now and set back to the last resolution you configured on that monitor.
Underscan/overscan options aren't supported as driver workarounds yet (bug tracked here), but if you can't configure your monitor to scan out 1:1, you may have success playing with xrandr --transform.
I don't think you can do that (yet).
Raspberrypi.org forum user spl23, described as a 'Raspberry Pi Engineer & Forum Moderator', reported in October 2016 that:
The GL driver currently ignores overscan/underscan settings, which is what is causing your problem. As we said, it's experimental - it's not finished yet! Work is ongoing to complete it, which will include having it respect overscan, but for the time being, your only option is to find a different monitor which will work properly with the fixed overscan in the GL driver, or to turn the GL driver off and use the Underscan option in Raspberry Pi Configuration to get your desktop to line up with the edges of your monitor.
We are working on improvements to the GL driver at the moment, but I'm afraid I can't as yet give any concrete timescale for when this will be fixed.
