Previously Alacritty has initialized all lines in the buffer as soon as
it is started. This had the effect that terminals which aren't making
use of the scrollback buffer yet, would still consume large amounts of
memory, potentially even freezing the system at startup.
To resolve this problem, the grid is now dynamically resized in chunks
of `1000` rows. The initial size is just the visible area itself, then
every time lines are written to the terminal emulator, the grid storage
is grown when required.
With the worst-case scenario of having 100_000 lines scrollback
configured, this change improves startup performance at the cost of
scrolling performance.
On my machine the startup changes from ~0.3 to ~0.2 seconds.
The scrolling performance with large throughput is not affected, however
it is slowed down when the number of lines scrolled are close to the
100_000 configured as scrollback. The most taxing benchmark I've found
for this was running `yes | dd count=500 > 500.txt` (note the relatively
small file size). This will cause a slowdown on the first run from 0.05s
to 0.15s. While this is significant, it lines up with the time saved at
startup.
This fixes#1236.
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.
Because there is no good way to store invisible lines in a backwards-
and forwards-compatible way, they buffer now gets truncated before
dumping the state of a grid when creating a ref-test.
This involved a few workaround of which a few required adding additional
methods which are only used in ref-tests, these should be minimal
though.
Since this required the creation of a truncation method anyways, some
logic has been added which automatically truncates the invisible buffer
when there are more than X (set to 100) invisible lines. This should not
impact performance because it rarely occurs, but it could save a bit of
memory when the history size is shrunk during runtime (see #1293).
This also adds an optional `config.json` file to the ref-test output
where it is possible to manually specify variables which should override
config defaults, this has been used only for history_size so far.
Creating a new ref-test does also still work, so there was no regression
here, if history size is altered, the config.json just has to be created
manually with the content `{"history_size":HIST_SIZE}`, where
`HIST_SIZE` is the desired history size.
The old grid_reset test expected the complete grid to be reset, but
instead of resetting the whole grid the `grid.scroll_limit` is just set
to `0` now. This leads to the rest of the grid still containing the old
information.
To fix this test it has simply be re-recorded. The new tests now still
contains the complete history but it is checked that the `scroll_limit`
is correctly reset.
In the current scrollback PR the `reset` command does not affect the
scrollback history. To make sure the terminal is properly reset, it
should clear the scrollback history.
This commit fixes this by creating a new and empty grid whenever `reset`
is executed. It takes the current dimensions and history size from the
old grid.
Right now there's an empty ref-test called `grid_reset` without any
content, this should be implemented once #1244 is resolved.
This fixes#1242.
