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commands: refactor scrollback up/down

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When moving the viewport in the scrollback (i.e. “scrolling”), we need
to ensure the viewport is not moved past the beginning, or end, of the
scrollback.

This was previously accomplish by first limiting the number of lines
to scroll to the number of visible rows (i.e the viewport _size_), and
by adjusting the viewport after moving it, to ensure it doesn’t point
into an uninitialized scrollback area etc.

I.e. the implementation was _reactive_.

This patch rewrites the logic to be _proactive_; we now calculate
_where_ the beginning (or end) of the scrollback is, and then how many
lines there is from there, to the viewport. This is our _maximum_
number of lines to scroll.

When done correctly (which I hope this patch does), this allows us to
remove _all_ checks after moving the viewport - we already _know_ it’s
correct, and valid.

As a bonus, we can remove the old limit, where scrolling was only
allowed to be at most a single page.
This commit is contained in:
Daniel Eklöf 2022-02-23 18:59:06 +01:00
parent f76c9e77f1
commit cb43c58150
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GPG key ID: 5BBD4992C116573F
1 changed files with 62 additions and 92 deletions
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154
commands.c
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@ -18,68 +18,58 @@ cmd_scrollback_up(struct terminal *term, int rows)
if (urls_mode_is_active(term))
return;
rows = min(rows, term->rows);
xassert(term->grid->offset >= 0);
const struct grid *grid = term->grid;
const int offset = grid->offset;
const int view = grid->view;
const int grid_rows = grid->num_rows;
const int screen_rows = term->rows;
int new_view = term->grid->view - rows;
while (new_view < 0)
new_view += term->grid->num_rows;
new_view %= term->grid->num_rows;
int scrollback_start = (offset + screen_rows) & (grid_rows - 1);
xassert(new_view >= 0);
xassert(new_view < term->grid->num_rows);
/* Avoid scrolling in uninitialized rows */
while (term->grid->rows[new_view] == NULL)
new_view = (new_view + 1) % term->grid->num_rows;
if (new_view == term->grid->view) {
/*
* This happens when scrolling up in a newly opened terminal;
* every single line (except those already visible) are
* uninitialized, and the loop above will bring us back to
* where we started.
*/
return;
/* Part of the scrollback may be uninitialized */
while (grid->rows[scrollback_start] == NULL) {
scrollback_start++;
scrollback_start &= grid_rows - 1;
}
/* Don't scroll past scrollback history */
int end = (term->grid->offset + term->rows - 1) % term->grid->num_rows;
if (end >= term->grid->offset) {
/* Not wrapped */
if (new_view >= term->grid->offset && new_view <= end)
new_view = (end + 1) % term->grid->num_rows;
/* Number of rows to scroll, without going past the scrollback start */
int max_rows = 0;
if (view + screen_rows >= grid_rows) {
/* View crosses scrollback wrap-around */
xassert(scrollback_start <= view);
max_rows = view - scrollback_start;
} else {
if (new_view >= term->grid->offset || new_view <= end)
new_view = (end + 1) % term->grid->num_rows;
if (scrollback_start <= view)
max_rows = view - scrollback_start;
else
max_rows = view + (grid_rows - scrollback_start);
}
while (term->grid->rows[new_view] == NULL)
new_view = (new_view + 1) % term->grid->num_rows;
rows = min(rows, max_rows);
if (rows == 0)
return;
int new_view = (view + grid_rows) - rows;
new_view &= grid_rows - 1;
xassert(new_view != view);
xassert(grid->rows[new_view] != NULL);
#if defined(_DEBUG)
for (int r = 0; r < term->rows; r++)
xassert(term->grid->rows[(new_view + r) % term->grid->num_rows] != NULL);
xassert(grid->rows[(new_view + r) & (grid->num_rows - 1)] != NULL);
#endif
LOG_DBG("scrollback UP: %d -> %d (offset = %d, end = %d, rows = %d)",
term->grid->view, new_view, term->grid->offset, end, term->grid->num_rows);
if (new_view == term->grid->view)
return;
int diff = -1;
if (new_view < term->grid->view)
diff = term->grid->view - new_view;
else
diff = (term->grid->num_rows - new_view) + term->grid->view;
view, new_view, offset, end, grid_rows);
selection_view_up(term, new_view);
term->grid->view = new_view;
if (diff >= 0 && diff < term->rows) {
term_damage_scroll(term, DAMAGE_SCROLL_REVERSE_IN_VIEW, (struct scroll_region){0, term->rows}, diff);
term_damage_rows_in_view(term, 0, diff - 1);
if (rows < term->rows) {
term_damage_scroll(
term, DAMAGE_SCROLL_REVERSE_IN_VIEW,
(struct scroll_region){0, term->rows}, rows);
term_damage_rows_in_view(term, 0, rows - 1);
} else
term_damage_view(term);
@ -95,65 +85,45 @@ cmd_scrollback_down(struct terminal *term, int rows)
if (urls_mode_is_active(term))
return;
if (term->grid->view == term->grid->offset)
const struct grid *grid = term->grid;
const int offset = grid->offset;
const int view = grid->view;
const int grid_rows = grid->num_rows;
const int screen_rows = term->rows;
const int scrollback_end = offset;
/* Number of rows to scroll, without going past the scrollback end */
int max_rows = 0;
if (view <= scrollback_end)
max_rows = scrollback_end - view;
else
max_rows = offset + (grid_rows - view);
rows = min(rows, max_rows);
if (rows == 0)
return;
rows = min(rows, term->rows);
xassert(term->grid->offset >= 0);
int new_view = (term->grid->view + rows) % term->grid->num_rows;
xassert(new_view >= 0);
xassert(new_view < term->grid->num_rows);
/* Prevent scrolling in uninitialized rows */
bool all_initialized = false;
do {
all_initialized = true;
for (int i = 0; i < term->rows; i++) {
int row_no = (new_view + i) % term->grid->num_rows;
if (term->grid->rows[row_no] == NULL) {
all_initialized = false;
new_view--;
break;
}
}
} while (!all_initialized);
/* Don't scroll past scrollback history */
int end = (term->grid->offset + term->rows - 1) % term->grid->num_rows;
if (end >= term->grid->offset) {
/* Not wrapped */
if (new_view >= term->grid->offset && new_view <= end)
new_view = term->grid->offset;
} else {
if (new_view >= term->grid->offset || new_view <= end)
new_view = term->grid->offset;
}
int new_view = (view + rows) & (grid_rows - 1);
xassert(new_view != view);
xassert(grid->rows[new_view] != NULL);
#if defined(_DEBUG)
for (int r = 0; r < term->rows; r++)
xassert(term->grid->rows[(new_view + r) % term->grid->num_rows] != NULL);
xassert(grid->rows[(new_view + r) & (grid_rows - 1)] != NULL);
#endif
LOG_DBG("scrollback DOWN: %d -> %d (offset = %d, end = %d, rows = %d)",
term->grid->view, new_view, term->grid->offset, end, term->grid->num_rows);
if (new_view == term->grid->view)
return;
int diff = -1;
if (new_view > term->grid->view)
diff = new_view - term->grid->view;
else
diff = (term->grid->num_rows - term->grid->view) + new_view;
view, new_view, offset, end, grid_rows);
selection_view_down(term, new_view);
term->grid->view = new_view;
if (diff >= 0 && diff < term->rows) {
term_damage_scroll(term, DAMAGE_SCROLL_IN_VIEW, (struct scroll_region){0, term->rows}, diff);
term_damage_rows_in_view(term, term->rows - diff, term->rows - 1);
if (rows < term->rows) {
term_damage_scroll(
term, DAMAGE_SCROLL_IN_VIEW,
(struct scroll_region){0, term->rows}, rows);
term_damage_rows_in_view(term, term->rows - rows, screen_rows - 1);
} else
term_damage_view(term);