On 10/05/2018 12:56 PM, Michel Dänzer wrote:
On 2018-10-05 6:21 p.m., Kazlauskas, Nicholas wrote:
On 10/05/2018 04:10 AM, Pekka Paalanen wrote:
2. User preference
A toggle on the desktop environment's display settings
application to allow or disallow VRR. After all, video mode
configuration is here too, and ideally applications should not
mess with the video mode directly.
[...]
User preference can be handled as part of the DDX driver with something
like an X Option. Dropping the variable_refresh_enabled property in
favor of this works. This covers 2.
The Xorg driver can expose a RandR output property, even if the kernel
doesn't expose a corresponding connector property. See e.g. the TearFree
output property in xf86-video-amdgpu.
The new configuration property for the DDX side of things does pretty
much that.
I also believe that it would be useful to expose vmin/vmax to userspace
as properties, so that display servers and apps can plan ahead on when
they will render. I suppose that can be left for later when someone
starts working on userspace taking advantage of it, so that the proper
userspace requirement for new UABI is fulfilled.
Knowing the vmin/vmax could potentially be useful for testing but most
applications shouldn't be trying to predict or adjust rendering based on
these.
FWIW, recent research indicates that this is necessary for perfectly
smooth animation without micro-stuttering, even with VRR.
This was brought up in previous RFCs about this but I'm not really
convinced by the research methodology and the results from those threads.
Targeting the max vrefresh of the display (which is known without
additional properties) should be best for prediction since anything
lower would be inherently less smooth by definition.
Nicholas Kazlauskas
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