On Thursday, March 12, 2020 11:45 AM, Michel Dänzer <michel@xxxxxxxxxxx> wrote: > On 2020-03-11 9:09 p.m., Simon Ser wrote: > > > Hi all, > > I've been working on adding VRR support to Sway [1] (a Wayland > > compositor). The compositor just sets the VRR_ENABLED property. > > This works fine for some screens, but causes flcikering for other > > screens as expected [2]. Fixing the flickering is something we've > > talked about last XDC [3]. The flickering is caused by physical > > limitations of the screen: changing the refresh rate too quickly > > results in brightness issues. > > The approach taken by xf86-video-amdgpu is to only enable VRR if an app > > is fullscreen and not present in a special Mesa blacklist (e.g. Firefox > > is in the blacklist because it doesn't render at a fixed interval). > > For Wayland, I'd prefer to avoid having a blacklist. I'd like to be > > able to use VRR in the general case (not just for fullscreen apps). > > A way to fix the flickering would be to implement a slew rate and make > > it so refresh rate variations are capped by the slew rate. > > One potential issue I see with this is the cursor, which can feel > awkward if it only moves at 30 Hz. I wonder if a slew rate which can > reliably prevent flickering allows the framerate to ramp up quickly > enough for this not to be annoying. Thanks for pointing this out, that's a valid concern. My VRR monitor has a 40-60Hz VRR range. With the current Sway implementation and drm_monitor [1], I can check that moving my mouse on the monitor makes the refresh interval go from ~25ms to ~16.6ms (ie. 40Hz to 60Hz). Right now there's no slew rate, so it goes from min to max instantly. I don't notice any flickering and there's no lag. Looking at the list of monitors [2] on Wikipedia, it doesn't seem like there's any monitor supporting less than 35Hz. We'd need to perform experiments on more hardware, but flickering has been noticed by our users on higher-end monitors which support 144Hz. I think the slew rate would prevent going from 35Hz to 144Hz directly, but probably not from 40Hz to 60Hz. I think that would be acceptable. If it's not, we can always tweak the minimum refresh rate. tl;dr need to test on more hardware, but should probably be fine. [1]: https://github.com/emersion/drm_monitor [2]: https://en.wikipedia.org/wiki/FreeSync#List_of_supported_monitors _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
