Use four threads to load the four primary font variants - normal,
bold, italic and bold italic.
This speeds up initial startup, and reloading of fonts on a DPI
change.
That is, deal with monitors being unplugged.
At least on Sway 1.4, surfaces are not unmapped before the output is
removed. Thus, in addition to free:ing the monitor resources, we also
need to update all terminals that are mapped on this output - remove
the output from their "mapped on" list.
action_clear() is in the super hot code path. Avoid resetting utf8
state there, as utf8 input is relatively uncommon.
Instead, reset it when we explicitly enter any of the utf8 collecting
states, as this is exactly the point where we need it.
This feature lets foot combine e.g. "a\u0301" to "á".
We first check if the current character (that we're about to print) is
a combining character, by checking if it's in one of the following
ranges:
* Combining Diacritical Marks (0300–036F), since version 1.0, with
modifications in subsequent versions down to 4.1
* Combining Diacritical Marks Extended (1AB0–1AFF), version 7.0
* Combining Diacritical Marks Supplement (1DC0–1DFF), versions 4.1 to 5.2
* Combining Diacritical Marks for Symbols (20D0–20FF), since version
1.0, with modifications in subsequent versions down to 5.1
* Combining Half Marks (FE20–FE2F), versions 1.0, with modifications
in subsequent versions down to 8.0
If it is, we check if the last cell appears to contain a valid symbol,
and if so, we attempt to compose (combine) the last cell with the
current character, using utf8proc.
If the result is a combined character, we replace the content in the
previous cell with the new, combined character.
Thus, if you select and copy the printed character, you would get
e.g. "\u00e1" instead of "a\u0301".
This feature can be disabled. By default, it is enabled if the
utf8proc library is found, but can be explicitly disabled, or enabled,
with 'meson -Dunicode-combining=disabled|enabled'.
Now that both tllist and fcft use meson.override_dependency(), we can
use the simpler form of fallback in our dependency call().
This requires meson >= 0.53, tllist >= 1.0.1 and fcft >= 2.0.0
At this point, we're not mapped, but we should have all the outputs
initialized. Which means we can at least guess which subpixel mode to
use.
If that turns out to be wrong, something we'll detect when we're
mapped, we'll just have to re-render.
These lists are typically empty when we destroy the terminal. However,
if we had queued up damage, and then manage to destroy the terminal
instance before the last changes were rendered, then they will *not*
be empty.
Found by the address sanitizer.
