The Linux OpenGL ABI does not guarantee that glXSwapIntervalEXT will be
exported statically from any library, and indeed on some systems this
function does not link at load time, e.g. with amdgpu-pro. All other
GLX functions that we use are from GLX 1.0, which is guaranteed to be
exported statically.
This commit solves this issue by using glXGetProcAddressARB to load the
function. Note that only the ARB version of glXGetProcAddress is
guaranteed to exist by the Linux OpenGL ABI, which is why we must use
it.
External events like launching other applications can cause latency
spikes while X11 initializes the application, we should only start
adjusting our delay if we see excessive skips over a 1s period.
Invalidating the entire window on an Expose event causes poor WM
performance when dragging the window around. Instead flag to redraw and
wait for the expose events to stop for 100ms before doing it.
X11 needs to calibrate to get the best possible latency, as such it
needs the scene to render so that the render time of the scene can be
accounted for in the delay calculation.
XPresent doesn't give us the time before presentation, but the time just
after. This code calculates and calibrates a delay to sleep for before
signaling the wait event for render when using jitRender
Version 3 does not send xdg_output.done events, instead guaranteeing that
all xdg_output.* events are sent before wl_output.done. This saves us from
doing the work twice.
The method used is not guaranteed to work on all Wayland compositors,
so offer a way out. We need to support it anyways in case xdg_output
or wp_viewporter protocols are not available.
Currently, we scale the desktop up to the next largest integer, and rely on
the wayland compositor to scale it back down to the correct size.
This is obviously undesirable.
In this commit, we attempt to detect the actual fractional scaling by finding
the current active mode in wl_output, and dividing it by the logical screen
size reported by xdg_output, taking into consideration screen rotation.
We then use wp_viewporter to set the exact buffer and viewport sizes if
fractional scaling is needed.
