Create code file for common direct mode code.
Make common functions take generic parameters.
Use common code in randr and nvidia back ends.
Remove redunant includes.
In favor of own struct to determine best available mode.
The loop now also starts as one, as we do not need compare the 0th mode
it itself and returns if there is only one mode.
The code was already essentialy C, just needed to replace the pairs with
structs and the vector with an array, it was fixed length anyway.
The code feels more natural in C.
In order to save redundancy with initializing empty fields with NULL / 0
values and improve readability of the Vulkan code.
This patch also uses struct initializers where possible.
This essentially reverts 1eae45212e.
Since there currently is no Vulkan extension that takes XCB handles to
aqcuire the display Xlib interop needs to be used.
Before this patch Monado was opening connections for both APIs, which
introduced overhead.
Even though all XCB handles can be casted to Xlib ones, this cannot be
done with the main xcb_connection_t / Display. In it's design the
interop between both APIs can create a xcb_connection_t from a XCB
handle, but not the other way round. So in an interop case the Xlib
connection is the main one, since it's on a higher level.
More information on this can be found here:
https://xcb.freedesktop.org/MixingCalls/
Unfortunately the clean solution for this would be to specify a Vulkan
extension that takes XCB handles. This would make sense since Vulkan
is aware of XCB in other parts of the API as well. In Mesa the Xlib
structs will be ultimately casted to XCB.
According the XCB documentation the reply structs must be freed. I found
this when running a minimal example related to the direct mode code in
valgrind.
This allows transitive dependencies to work easier and improves compatibility.
It takes a little bit more storage at build time, and possibly a little extra time.
The variable should be set to the index in the enumeration of a modes according to VK_KHR_display.
Monado can print a list of available modes with their indices with the env var XRT_COMPOSITOR_PRINT_MODES=1.
