To do text reflow, we only need to know if a line has been explicitly
linebreaked or not. If not, that means it wrapped, and that we
should *not* insert a linebreak when reflowing text.
When reflowing text, when reaching the end of a row in the old grid,
only insert a linebreak in the new grid if the old row had been
explicitly linebreaked.
Furthermore, when reflowing text and wrapping a row in the new grid,
mark the previous row as linebreaked if either the last cell was
(the last column in the last row) empty, or the current cell (the
first column in the new row) is empty. If both are non-empty, then we
assume a linewrap.
When cursor.lcf is set, that means the cursor column was *not*
incremented when we printed the last character. Thus, we should *not*
decrement the column before setting the linefeed bit.
To handle text reflow correctly when a line has a printable character
in the last column, but was still line breaked, we need to track the
fact that the slave inserted a line break here.
Otherwise, when the window width is increased, we'll end up pulling up
the next line, when we really should have inserted a line break.
When term_print() was implemented, it introduced a regression where
printing a character when the last cursor was in the last column on a
line would print the character in the wrong column.
This is because term_print() retrieved a pointer to the current
cell *before* line wrapping (and possibly inserting empty cells).
This means that the read handler now has to keep reading until we get
EAGAIN.
But it also means we don't have to flip the EPOLLOUT flag in the FDM
handler back and forth when writing to the PTY.
With a bad behaving client (e.g. 'less' with mouse support enabled),
we can end up with a *lot* of xcursor updates (so much, that we
flooded the wayland socket before we implemented a blocking
wayl_flush()).
Since there's little point in updating the cursor more than once per
frame interval, use frame callbacks to throttle the updates.
This works more or lesslike normal terminal refreshes:
render_xcursor_set() stores the last terminal (window) that had (and
updated) the cursor.
The renderer's FDM hook checks if we have such a pending terminal set,
and if so, tries to refresh the cursor.
This is done by first checking if we're already waiting for a callback
from a previous cursor update, and if so we do nothing; the callback
will update the cursor for the next frame. If we're *not* already
waiting for a callback, we update the cursor immediately.
wl_display_dispatch() calls poll(), which is unnecessary since we
already know the FD is readable.
Use the more lower level wl_display_read_events() +
wl_display_dispatch_pending().
These require wl_display_prepare_read() to have been called.
The idea is to call wl_display_prepare_read() **before** calling
poll().
Thus, we do this more or less last in wayl_init(), and at the **end**
of the FDM handler.
However, having taking this lock also means we no longer can call
wl_display_roundtrip() directly (it will hang).
So, add a wrapper, wayl_roundtrip(), that cancels the read intent,
does the roundtrip, and then re-acquires the read intent.
Instead of having `wayl_win_init()` call
`wl_display_roundtrip()` (which it itself doesn't need), call it from
`term_init()`.
This allows us to add ourselves (the new terminal instance) to the
terminal list in the wayland backend, before triggering the wayland
events caused by `wayl_win_init()`.
This is turn allows the wayland backend to find/lookup the new
terminal when those events occur..
This allows us to measure the time between to refresh delays. That is,
when we decide to delay a refresh, we store the current time.
If we hit that code path _again_, without having refreshed, we
calculate the time that has passed.
This gives us an estimate for how we should set our lower delay
timeout.
This is of course application dependent, but is still much better than
simply guessing a value...
