Now, only cells that have been used are cleared. This is achieved by
using a "occupied" memo on the Row itself. The value, `occ`, is updated
wherever the Row is accessed mutably, and it's cleared to zero in
Row::reset.
The tests for grid scroll_up and scroll_down were updated to include a
test on the value `occ` and slightly refactored, but are otherwise
equivalent to the previous implementation of those tests.
Because of the change to the `Row` struct, the ref tests were updated so
Deserialization keeps working as expected.
Some tests are still not passing, though.
A migration script was added to migrate serialized grids from
pre-scrollback to the current format. The script is included with this
commit for completeness, posterity, and as an example to be used in the
future.
A few tests in grid/tests.rs were removed due to becoming irrelevant.
Since landing the patch adding transparency support to Alacritty,
there's been an issue where othewise solid background cells were also
being rendered partially transparent. Now, all filled background cells
are rendered fully opaque.
Some logic was added to support discarding filled backgrounds which had
the same color as the default background. This means that, if the
default background is #000 and a cell has that background, it will never
be rendered opaque. This may not be correct.
Note that many truecolor vim color schemes print spaces for default
colored background cells. Performance can be dramatically improved by
using ctermbg=NONE guibg=NONE to skip rendering those cells.
The script uses the recently added _NET_WM_PID window property for
finding the program running in Alacritty, fetching its working
directory, and spawning a new Alacritty using that directory.
