Add support for XCB

[tomaka]

[kvark]

Some machines don't support VK_KHR_xlib_surface but do support VK_KHR_xcb_surface, so this is a compatibility concern:

Instance Extensions     count = 3
        VK_KHR_surface                  : extension revision 25
        VK_KHR_xcb_surface              : extension revision  5
        VK_EXT_debug_report             : extension revision  2

[kvark]

Found this library as a potential workaround: https://github.com/Aatch/rust-xcb

[nicokoch]

Just a heads up for anyone searching a workaround.

The intel linux driver does indeed support xlib, but it has to be enabled at compile time.
You can compile the vulkan driver yourself with VK_KHR_xlib_surface enabled by enabling
-DVK_USE_PLATFORM_XLIB_KHR.

For anyone using archlinux, I have submitted a feature request to their bug tracker (https://bugs.archlinux.org/task/50160). It looks like they are working on it (or at least are aware of the problem). For other distros, you can try submitting a bug report to their corresponding bug tracker.

[kvark]

Thanks for the info @nicokoch

[mikedilger]

With xlib I'm experiencing (in vulkan) get_physical_device_surface_formats_khr() doesn't return until the window is focused. With xcb (in a separate C++ program - Sascha Willems demos) this doesn't happen, the window draws irrespective of focus. I can't be sure the reason for this behavioral difference is xlib vs xcb, but it is looking that way, in which case I prefer xcb and +1 this issue.

[francesca64]

Is this still relevant?

[tomaka]

This is still relevant, but not really a priority.