Use a basic linked list to store the currently active mappings.
Note that we don't actually need to implement a full lock-free
atomic linked list here. The signal handler will never write to
the list, it will only read it. Only the main thread will write.
We need to always expose a consistent view of the list to the
signal handler (the main thread might be interrupted at any point
by the signal handler).
This is a re-implementation of wl_shm. The motivations for using
this over the one shipped in libwayland are:
- Properly handle SIGBUS when accessing a wl_buffer's underlying
data after the wl_buffer protocol object has been destroyed.
With the current code, we just crash if the client does that
and then shrinks the backing file.
- No need to fight the wl_shm_buffer API anymore. This was awkward
because we weren't notified when clients created a wl_shm buffer,
and this doesn't play well with our wlr_buffer abstraction.
- Access to the underlying FD. This makes it possible to forward
the wl_shm buffer to a parent compositor with the Wayland/X11
backends.
- Better stride checks. We can use our format table to ensure that
the stride is consistent with the bpp and width.
The concept of a persistent accumulated surface offset is wrong
from a protocol point-of-view. wl_surface.offset is tied to a
commit, its interpretation depends on the surface role.
For example, with the following sequence:
wl_surface@1.offset(1, 1)
wl_surface@1.commit()
wl_pointer@2.set_cursor(wl_surface@1, 42, 42)
The final cursor hotspot is (42, 42): the commit which happened
before the set_cursor request has no impact on the hotspot
computation.
The wlr_output_cursor logic already uses wlr_surface.current.{dx,dy}.
wlr_scene's drag icon doesn't, update it accordingly.
This allows compositors to indicate which features they support,
and is required to eventually make this API stable.
References: https://github.com/swaywm/sway/issues/7260
If a fixed mode matching the user requirements is available, use
that. This avoids generating the mode with GTF or CVT in the DRM
backend, and instead uses mode timings advertised by the output.
References: https://gitlab.freedesktop.org/wlroots/wlroots/-/issues/3514
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.
