Prior to this commit, a backing buffer with scale 1 was always created for
a scaled_scene_buffer before showing it, and backing buffers for specific
scales were created on output_enter events.
This commit removes this redundant re-renderings by calling
wlr_scene_buffer_set_dest_size() upon scaled_scene_buffer creation just to
receive output_enter events and delaying the first rendering to the first
output_enter event.
I needed to add font_get_buffer_size() to obtain the size of a font buffer
without actually creating it.
Arrow signs are specific to submenu items, so they would be more natural
to be handled in menu.c rather than accepting "arrow" in
font_buffer_create().
Also I allowed non-positive numbers for max_width in font_buffer_create(),
in which case the natural font width is used as the buffer width.
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.
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).
