Support for high bit depth screencopy buffers

[mstoeckl]

wlroots will eventually be able to render to 10-bit or higher internal buffers. (See swaywm/wlroots#1378.) † The internal buffers determine what buffer formats are requested by zwlr_screencopy_frame_v1.buffer; so for example, with 10-bit buffers, XBGR2101010 or ABGR2101010 would be sent; and with half-float formats, ABGR16161616F or XBGR16161616F would be sent.

It will probably be a long time before support for these formats will be needed; but I am making this issue now, as this task may be difficult. Currently, ffmpeg does not have any direct equivalents for the above formats, so it may be necessary to add a format conversion step to wf-recorder. (For example, the closest thing to WL_SHM_FORMAT_XBGR2101010 is AV_PIX_FMT_X2RGB10LE, which has red and blue channels switched.)

† In case you want to test wlroots with higher bit depth earlier, I have made experimental branches for 10 and 16float internal depth; 16 bit depth may become possible in a few months. Edit: wlroots now supports changing the render buffer format; I made a Sway PR, swaywm/sway#6475, which adds a setting to control this.

[ammen99]

Wouldn't it make more sense to add support for these formats to ffmpeg, at least for conversion?

Edit: I am not really familiar with ffmpegs codebase but I assume someone else might be.

[mstoeckl]

Wouldn't it make more sense to add support for these formats to ffmpeg, at least for conversion?

Yes, that would be ideal.

[mstoeckl]

I've filed a ticket about supporting XBGR2101010 at https://trac.ffmpeg.org/ticket/9421 , and have attached a (first draft) patch to add the format. (I'll try to submit a proper version to ffmpeg-devel later.) See https://github.com/mstoeckl/wf-recorder/commit/dca878c0022ed2d3a81f8daafde43f514d0e6406 for the changes needed to add XBGR2101010 support, plus changes needed to build against ffmpeg git master.

(It doesn't look like ffmpeg has any code at all to convert half-float formats, so I'll leave figuring out XBGR16161616F and ABGR16161616F support to future people.)

[mstoeckl]

AV_PIX_FMT_X2BGR10LE is now in FFmpeg git master, and will probably be available when the next major FFmpeg release is made; based on recent releases, that should take less than a year.