Based on five calls:
wlr_render_timer_create - creates a timer which can be reused across
frames on the same renderer
wlr_renderer_begin_buffer_pass - now takes a timer so that backends can
record when the rendering starts and finishes
wlr_render_timer_get_time - should be called as late as possible so that
queries can make their way back from the GPU
wlr_render_timer_destroy - self-explanatory
The timer is exposed as an opaque `struct wlr_render_timer` so that
backends can store whatever they want in there.
This is to allow for compositors that want to be more implicit about
how their scene is organized. Such a compositor may want to walk up
at a certain scene node to find something such as a surface to focus on.
Now, it is checked whether an output pixel corresponds to an integer
number of buffer pixels; if it doesn't, the region is altered to take
this into account.
This allows the backend to have access to the frame damage, as
reported by the scanned-out client. Some KMS drivers can make use
of it (e.g. for PSR, or optimized USB transfers in the GUD driver),
and the Wayland/X11 backends forward it to the parent compositor.
If a new buffer is set for a buffer node, we must update the entire
node unconditionally if the buffer size changes, or the buffer is given
a buffer where it was previously NULL.
While we're here, let's avoid calling scene_node_update on just damage
updates. If the caller hasn't given us a damage region we just assume
the whole buffer.
If the area calculations for output overlap overflow a signed int, we
may not consider it to be a primary output. Turn this into an unsigned
type so this happens less frequently.
Additionally, it is possible the overflow would produce 0, we can handle
this by simply changing the comparison to more than or equal.
While we're here, let's assert that we always assign a primary output
if there are any intersecting outputs.
Originally, I thought that we could safely subtract opaque regions
from the background even if the black rect optimization was kicking in.
This is wrong because a scene node that isn't fully occluded will still
appear in the render list even if its partially under a black rect. We
need to make sure that while culling the background, we only consider
opaque regions that are also visible. This will fix the black rect
optimization with the background.
We don't need to worry about the black rect optimization here (that
always assumes that there will be a black background) because the
background is culled based on the render list. That means if a black rect
is removed, the visibility will reach all the way to the bottom forcing
the renderer to clear the area not breaking the assumption.