Implementers can define impl->equal() which compares two
scaled-scene-buffers so that buffers are not allocated for visually
duplicated scaled-scene-buffers.
Currently this mechanism isn't applied for scaled-font-buffers since we
haven't defined impl->equal() for it.
This allows implementations of the interface to share a single
wlr_buffer for multiple wlr_scene_buffer nodes and still make
the scaled-scene-buffer handle the buffer drops.
wlr_scene_buffer holds an implicit lock while using a wlr_buffer
and scaled-scene-buffer.c holds additional locks for as long as
a buffer is within its internal cache.
This should ensure that a shared wlr_buffer never gets actually
dropped even if wlr_buffer_drop() has been called by another
scaled-scene-buffer instance using the same wlr_buffer.
Add buffer_adopt_cairo_surface(), which allows wrapping an existing
cairo image surface in a struct lab_data_buffer. This is useful when
loading PNGs since most will be loaded as ARGB32 already.
Fix a memory leak in the non-ARGB32 PNG case, where we do still need to
paint to a new image surface -- we were leaking the original surface.
Eliminate an unnecessary temporary image surface in SVG loading and just
render the SVG to the image surface held by the lab_data_buffer.
I also cleaned up and clarified the buffer API a bit:
- Add a pointer to the held cairo_surface_t (so we can still access it
if there is no cairo_t).
- Remove the free_on_destroy bool (it was always true).
- Rename unscaled_width/height to logical_width/height and add an
explanatory comment. It was unclear what "unscaled" meant.
- Rename buffer_create_wrap() to buffer_create_from_data().
This is laying groundwork for some more icon fixes I am working on
(making sure icons are loaded and rendered at the correct scale).
