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sixel: implement private mode 80 - sixel scrolling

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When enabled (the default), sixels behave much like normal output; the
start where the cursor is, and the cursor moves with the
sixel. I.e. after emitting a sixel the cursor is left after the image;
either to the right, if private mode 8452 is enabled, or otherwise on
the next line. Terminal content is scrolled up if the sixel is larger
than the screen.

When disabled, sixels *always* start at (0,0), the cursor never moves,
and the terminal content never scrolls.

In other words, the ‘disabled’ mode is a much simpler mode.

All we need to do to support both modes is re-write the sixel-emitting
loop to:

* break early if we’re “out of rows”, i.e. we’ve reached the bottom of
  the screen.
* not linefeed, or move the cursor when scrolling is disabled

This patch also fixes a bug in the (new) implementation of private
mode 8452.

When emitting a sixel, we may break it up into smaller pieces, to
ensure a single sixel (as tracked internally) does not cross the
scrollback wrap-around.

The code that checked if we should do a linefeed or not, would skip
the linefeed on the last row of *each* such sixel piece. The correct
thing to do is to skip it only on the last row of the *last* piece.

I chose not to fix this bug in a separate patch since doing so would
have meant re-writing it again when implementing private mode 80.
This commit is contained in:
Daniel Eklöf 2021-02-26 09:28:03 +01:00
parent 792202bf29
commit 849427bf10
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GPG key ID: 5BBD4992C116573F
5 changed files with 75 additions and 41 deletions
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99
sixel.c
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@ -701,24 +701,43 @@ sixel_unhook(struct terminal *term)
const int stride = term->sixel.image.width * sizeof(uint32_t);
/*
* Need to 'remember' current cursor column.
* When sixel scrolling is enabled (the default), sixels behave
* pretty much like normal output; the sixel starts at the current
* cursor position and the cursor is moved to a point after the
* sixel.
*
* If we split up the sixel (to avoid scrollback wrap-around), we
* will emit a carriage-return (after several linefeeds), which
* will reset the cursor column to 0. If we use _that_ column for
* the subsequent image parts, the image will look sheared.
* Furthermore, if the sixel reaches the bottom of the scrolling
* region, the terminal content is scrolled.
*
* When scrolling is disabled, sixels always start at (0,0), the
* cursor is not moved at all, and the terminal content never
* scrolls.
*/
const int start_col = term->grid->cursor.point.col;
const bool do_scroll = term->sixel.scrolling;
/* Number of rows we're allowed to use.
*
* When scrolling is enabled, we always allow the entire sixel to
* be emitted.
*
* When disabled, only the number of screen rows may be used. */
int rows_avail = do_scroll
? (term->sixel.image.height + term->cell_height - 1) / term->cell_height
: term->rows;
/* Initial sixel coordinates */
int start_row = do_scroll ? term->grid->cursor.point.row : 0;
const int start_col = do_scroll ? term->grid->cursor.point.col : 0;
/* We do not allow sixels to cross the scrollback wrap-around, as
* this makes intersection calculations much more complicated */
while (pixel_rows_left > 0) {
const struct coord *cursor = &term->grid->cursor.point;
while (pixel_rows_left > 0 && rows_avail > 0) {
const int cur_row = (term->grid->offset + start_row) & (term->grid->num_rows - 1);
const int rows_left_until_wrap_around = term->grid->num_rows - cur_row;
const int usable_rows = min(rows_avail, rows_left_until_wrap_around);
const int cur_row = (term->grid->offset + cursor->row) & (term->grid->num_rows - 1);
const int rows_avail = term->grid->num_rows - cur_row;
const int pixel_rows_avail = rows_avail * term->cell_height;
const int pixel_rows_avail = usable_rows * term->cell_height;
const int width = term->sixel.image.width;
const int height = min(pixel_rows_left, pixel_rows_avail);
@ -755,12 +774,15 @@ sixel_unhook(struct terminal *term)
image.width, image.height,
img_data, stride);
/* Allocate space *first* (by emitting line-feeds), then insert */
pixel_row_idx += height;
pixel_rows_left -= height;
rows_avail -= image.rows;
/* Dirty touched cells, and scroll terminal content if necessary */
for (size_t i = 0; i < image.rows; i++) {
struct row *row = term->grid->cur_row;
struct row *row = term->grid->rows[cur_row + i];
row->dirty = true;
/* Mark cells touched by the sixel as dirty */
for (int col = image.pos.col;
col < min(image.pos.col + image.cols, term->cols);
col++)
@ -768,36 +790,37 @@ sixel_unhook(struct terminal *term)
row->cells[col].attrs.clean = 0;
}
if (i < image.rows - 1 || !term->sixel.cursor_right_of_graphics)
term_linefeed(term);
if (do_scroll) {
/*
* Linefeed, *unless* we're on the very last row of
* the final image (not just this chunk) and private
* mode 8452 (leave cursor at the right of graphics)
* is enabled.
*/
if (term->sixel.cursor_right_of_graphics &&
rows_avail == 0 &&
i >= image.rows - 1)
{
term_cursor_to(
term,
term->grid->cursor.point.row,
min(image.pos.col + image.cols, term->cols - 1));
} else {
term_linefeed(term);
term_carriage_return(term);
}
}
}
/*
* Position cursor
*
* Private mode 8452 controls where we leave the cursor after
* emitting a sixel:
*
* When disabled (the default), the cursor is positioned on a
* new line.
*
* When enabled, the cursor is positioned to the right of the
* sixel.
*/
term_cursor_to(
term,
term->grid->cursor.point.row,
(term->sixel.cursor_right_of_graphics
? min(image.pos.col + image.cols, term->cols - 1)
: 0));
_sixel_overwrite_by_rectangle(
term, image.pos.row, image.pos.col, image.rows, image.cols);
sixel_insert(term, image);
pixel_row_idx += height;
pixel_rows_left -= height;
if (do_scroll)
start_row = term->grid->cursor.point.row;
else
start_row -= image.rows;
}
term->sixel.image.data = NULL;