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.
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.
Instead of damaging the entire surface when rendering a cursor move,
we can use the EGL_KHR_swap_buffers_with_damage extension to only
damage the part of the window covered by the cursor. This should
reduce the cursor movement latency on Wayland.
The only addition to v4 was `wl_surface_damage_buffer`, which we do not
use.
This change should allow running on more compositors (even though v4 is
already old -- 5 years now).
Ref
3384f69ecf.
If the scale factor of an wl_output changes while the client is running,
the maximum scale factor is not updated. This may result in incorrect
scaling.
Therefore, when the scale factor is changed, we should generate a
resize event.
The Wayland display server is getting unwieldy due to the sheer size.
To make it easier to edit in the future, I split it into many components
based on logical boundaries.
