Cosmic comp setting max bpc for 10 bit displays to 16, is it really using XRGB16161616?

[kode54]

Is it really using a 16 bits per channel color format because my displays are reporting support for 10 bits per channel?

[Drakulix]

We should populate this with the highest amount of bits the display reports: https://github.com/pop-os/cosmic-comp/blob/master/src/backend/kms/device.rs#L842

If it doesn't (or supports more) we set it to 16, which indeed seems unnecessary, given we only ever use 10-bit currently. (Though there are reasons to use XRGB16161616 with HDR, so that might change.)

So we could definitely change this to 10 for now, I wonder if this has caused modeset errors.

[Drakulix]

#1518

[kode54]

Gotcha. Didn't know it was already using XRGB2101010 or so. Somehow Wayfire manages to use the same format and lead to a max_bpc of 8. Guess nobody is doing things right except for Plasma right now.

[Drakulix]

Somehow Wayfire manages to use the same format and lead to a max_bpc of 8.

So the internal format doesn't necessarily need to match the bits-per-channel on the wire.
But the result of such a configuration can be, that the display controller of your GPU will cut of extra bits, effectively limiting your output to 8-bits no matter with which precision the image was calculated.

This is why we try to default to a higher value, while leaving this configurable, as higher bits-per-channel will take up bandwidth, that might keep you from enabling additional displays. (Especially when chaining display-port displays.)