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LibVT: Improve scrolling performance

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Previously, we would remove lines from the buffer, create new lines and
insert them into the buffer when we scrolled. Since scrolling does not
always happen at the last line, this meant `Line` objects were
pointlessly moved forwards, and then immediately backwards.

We now swap them in-place and clear those lines that are "inserted". As
a result, performance is better and scrolling is smoother in `vim` and
`nano`.
This commit is contained in:
Daniel Bertalan 2021-06-05 08:55:33 +02:00 • committed by Andreas Kling
parent fe58d15b5b
commit 221ba1aac8
1 changed files with 27 additions and 20 deletions
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47
Userland/Libraries/LibVT/Terminal.cpp
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@ -775,20 +775,28 @@ void Terminal::scroll_up(u16 region_top, u16 region_bottom, size_t count)
// NOTE: We have to invalidate the cursor first.
invalidate_cursor();
if (!m_use_alternate_screen_buffer && max_history_size() != 0)
bool should_move_to_scrollback = !m_use_alternate_screen_buffer && max_history_size() != 0;
if (should_move_to_scrollback) {
for (size_t i = 0; i < count; ++i)
add_line_to_history(move(active_buffer().ptr_at(region_top + i)));
if (count == region_size) {
for (u16 row = region_top; row <= region_bottom; ++row)
active_buffer()[row].clear(Attribute());
return;
}
active_buffer().remove(region_top, count);
for (size_t i = 0; i < count; ++i)
active_buffer().insert(region_bottom - count + i + 1, make<Line>(m_columns));
for (u16 row = region_top; row <= region_bottom; ++row)
// Move lines into their new place.
for (u16 row = region_top; row + count <= region_bottom; ++row)
swap(active_buffer().ptr_at(row), active_buffer().ptr_at(row + count));
// Clear 'new' lines at the bottom.
if (should_move_to_scrollback) {
// Since we moved the previous lines into history, we can't just clear them.
for (u16 row = region_bottom + 1 - count; row <= region_bottom; ++row)
active_buffer().ptr_at(row) = make<Line>(columns());
} else {
// The new lines haven't been moved and we don't want to leak memory.
for (u16 row = region_bottom + 1 - count; row <= region_bottom; ++row)
active_buffer()[row].clear(Attribute());
}
// Set dirty flag on swapped lines.
// The other lines have implicitly been set dirty by being cleared.
for (u16 row = region_top; row <= region_bottom - count; ++row)
active_buffer()[row].set_dirty(true);
if (!m_use_alternate_screen_buffer && max_history_size() != 0)
m_client.terminal_history_changed();
@ -806,16 +814,15 @@ void Terminal::scroll_down(u16 region_top, u16 region_bottom, size_t count)
// NOTE: We have to invalidate the cursor first.
invalidate_cursor();
if (count == region_size) {
for (u16 row = region_top; row <= region_bottom; ++row)
active_buffer()[row].set_dirty(true);
return;
}
active_buffer().remove(region_bottom - count + 1, count);
for (size_t i = 0; i < count; ++i)
active_buffer().insert(region_top, make<Line>(m_columns));
for (u16 row = region_top; row <= region_bottom; ++row)
// Move lines into their new place.
for (int row = region_bottom; row >= static_cast<int>(region_top + count); --row)
swap(active_buffer().ptr_at(row), active_buffer().ptr_at(row - count));
// Clear the 'new' lines at the top.
for (u16 row = region_top; row < region_top + count; ++row)
active_buffer()[row].clear(Attribute());
// Set dirty flag on swapped lines.
// The other lines have implicitly been set dirty by being cleared.
for (u16 row = region_top + count; row <= region_bottom; ++row)
active_buffer()[row].set_dirty(true);
}