vo_dmabuf_wayland: unmap osd surface when not needed

[rmader]

Attaching a NULL buffer unmaps the surface, allowing compositors to skip blending the empty buffer.

Closes #12236

[llyyr]

This causes subtitles and osd to not be visible anytime the osd isn't explicitly being updated. To test you can load any video with subtitles, or press Shift+I to see stats.lua

[rmader]

Ah, indeed :/

So I guess that brings us back to what I mentioned in #12236:

Add a way to find out when a osd redraw ended up making it fully transparent (this is the hard part I didn't immediately found a solution for :) )

[Dudemanguy]

This causes subtitles and osd to not be visible anytime the osd isn't explicitly being updated.

Oh bummer, I had assumed that draw_osd would apply to subtitles being rendered as well but I guess not.

[rmader]

Oh bummer, I had assumed that draw_osd would apply to subtitles being rendered as well but I guess not.

The good news is: either the osd already has a way to detect the case - or introducing it would be helpful for other backends as well (I assume).

[Dudemanguy]

Yeah, this isn't really trivial unfortunately. The osd and sub visibility would need to be done in the core and then signaled in some way to the VOs that want it. Not sure what the right approach would be atm.

[rmader]

Turns out the backend does already give us what we need \o/
Updated, now working as expected for me.

[rmader]

Latest push does a small naming adjustment to bring the two new variables more in line.

[Dudemanguy]

Thanks for working on this!

[rmader]

@Dudemanguy sorry for the noise, but just out of interest: is there a point release planned in the coming months? It would be awesome if the upcoming distro releases would ship with this :)

[Dudemanguy]

No firm plans right now, but given that there's been several fixes since 0.36 and that release has some pretty user visible breakage (particularly in regards to subtitles; hopefully it's all fixed now), a point release wouldn't be unwarranted.