term: rename CELL_MULT_COL_SPACER -> CELL_SPACER, and change its definition

Instead of using CELL_SPACER for *all* cells that previously used
CELL_MULT_COL_SPACER, include the remaining number of spacers
following, and including, itself. This is encoded by adding to the
CELL_SPACER value.

So, a double width character will now store the character itself in
the first cell (just like before), and CELL_SPACER+1 in the second
cell.

A three-cell character would store the character itself, then
CELL_SPACER+2, and finally CELL_SPACER+1.

In other words, the last spacer is always CELL_SPACER+1.

CELL_SPACER+0 is used when padding at the right margin. I.e. when
writing e.g. a double width character in the last column, we insert a
CELL_SPACER+0 pad character, and then write the double width character
in the first column on the next row.

extract.c

@@ -113,7 +113,7 @@ extract_one(const struct terminal *term, const struct row *row,
 {
     struct extraction_context *ctx = context;
 
-    if (cell->wc == CELL_MULT_COL_SPACER)
+    if (cell->wc >= CELL_SPACER)
         return true;
 
     if (ctx->last_row != NULL && row != ctx->last_row) {

grid.c

@@ -473,9 +473,9 @@ grid_resize_and_reflow(
             grid, new_grid, new_row, &new_row_idx, &new_col_idx,    \
             new_rows, new_cols)
 
-#define print_spacer()                                                  \
+#define print_spacer(remaining)                                         \
         do {                                                            \
-            new_row->cells[new_col_idx].wc = CELL_MULT_COL_SPACER;      \
+            new_row->cells[new_col_idx].wc = CELL_SPACER + (remaining); \
             new_row->cells[new_col_idx].attrs = old_cell->attrs;        \
             new_row->cells[new_col_idx].attrs.clean = 1;                \
         } while (0)
@@ -541,7 +541,7 @@ grid_resize_and_reflow(
                 const struct cell *old_cell = &old_row->cells[c - empty_count + i];
                 wc = old_cell->wc;
 
-                if (wc == CELL_MULT_COL_SPACER)
+                if (wc >= CELL_SPACER)
                     continue;
 
                 if (wc >= CELL_COMB_CHARS_LO &&
@@ -554,7 +554,7 @@ grid_resize_and_reflow(
                 if (new_col_idx + max(1, wcwidth(wc)) > new_cols) {
                     /* Pad to end-of-line with spacers, then line-wrap */
                     for (;new_col_idx < new_cols; new_col_idx++)
-                        print_spacer();
+                        print_spacer(0);
                     line_wrap();
                 }
 
@@ -585,7 +585,7 @@ grid_resize_and_reflow(
             const struct cell *old_cell = &old_row->cells[c];
             for (size_t i = 0; i < width - 1; i++) {
                 xassert(new_col_idx < new_cols);
-                print_spacer();
+                print_spacer(width - i + 1);
                 new_col_idx++;
             }
 

ime.c

@@ -199,7 +199,7 @@ done(void *data, struct zwp_text_input_v3 *zwp_text_input_v3,
 
         for (int j = 1; j < width; j++) {
             cell = &seat->ime.preedit.cells[cell_idx + j];
-            cell->wc = CELL_MULT_COL_SPACER;
+            cell->wc = CELL_SPACER + width - j;
             cell->attrs = (struct attributes){.clean = 1};
         }
 
@@ -280,7 +280,7 @@ done(void *data, struct zwp_text_input_v3 *zwp_text_input_v3,
 
         /* Expand cursor end to end of glyph */
         while (cell_end > cell_begin && cell_end < cell_count &&
-               seat->ime.preedit.cells[cell_end].wc == CELL_MULT_COL_SPACER)
+               seat->ime.preedit.cells[cell_end].wc >= CELL_SPACER)
         {
             cell_end++;
         }

render.c

@@ -594,7 +594,7 @@ render_cell(struct terminal *term, pixman_image_t *pix,
     if (has_cursor && term->cursor_style == CURSOR_BLOCK && term->kbd_focus)
         draw_cursor(term, cell, font, pix, &fg, &bg, x, y, cell_cols);
 
-    if (cell->wc == 0 || cell->wc == CELL_MULT_COL_SPACER ||
+    if (cell->wc == 0 || cell->wc >= CELL_SPACER ||
         (unlikely(cell->attrs.conceal) && !is_selected))
     {
         goto draw_cursor;
@@ -1237,7 +1237,7 @@ render_ime_preedit_for_seat(struct terminal *term, struct seat *seat,
 
         /* Make sure we don't start in the middle of a character */
         while (ime_ofs < cells_needed &&
-               seat->ime.preedit.cells[ime_ofs].wc == CELL_MULT_COL_SPACER)
+               seat->ime.preedit.cells[ime_ofs].wc >= CELL_SPACER)
         {
             ime_ofs++;
         }
@@ -1249,7 +1249,7 @@ render_ime_preedit_for_seat(struct terminal *term, struct seat *seat,
     struct row *row = grid_row_in_view(term->grid, row_idx);
 
     /* Don't start pre-edit text in the middle of a double-width character */
-    while (col_idx > 0 && row->cells[col_idx].wc == CELL_MULT_COL_SPACER) {
+    while (col_idx > 0 && row->cells[col_idx].wc >= CELL_SPACER) {
         cells_used++;
         col_idx--;
     }
@@ -1268,11 +1268,11 @@ render_ime_preedit_for_seat(struct terminal *term, struct seat *seat,
     row->dirty = true;
 
     /* Render pre-edit text */
-    xassert(seat->ime.preedit.cells[ime_ofs].wc != CELL_MULT_COL_SPACER);
+    xassert(seat->ime.preedit.cells[ime_ofs].wc < CELL_SPACER);
     for (int i = 0, idx = ime_ofs; idx < seat->ime.preedit.count; i++, idx++) {
         const struct cell *cell = &seat->ime.preedit.cells[idx];
 
-        if (cell->wc == CELL_MULT_COL_SPACER)
+        if (cell->wc >= CELL_SPACER)
             continue;
 
         int width = max(1, wcwidth(cell->wc));

search.c

@@ -337,7 +337,7 @@ search_find_next(struct terminal *term)
                     row = term->grid->rows[end_row];
                 }
 
-                if (row->cells[end_col].wc == CELL_MULT_COL_SPACER) {
+                if (row->cells[end_col].wc >= CELL_SPACER) {
                     end_col++;
                     continue;
                 }
@@ -461,7 +461,7 @@ search_match_to_end_of_word(struct terminal *term, bool spaces_only)
         bool done = false;
         for (; end_col < term->cols; end_col++) {
             wchar_t wc = row->cells[end_col].wc;
-            if (wc == CELL_MULT_COL_SPACER)
+            if (wc >= CELL_SPACER)
                 continue;
 
             const struct composed *composed = NULL;

selection.c

@@ -234,7 +234,7 @@ find_word_boundary_left(struct terminal *term, struct coord *pos,
     const struct row *r = grid_row_in_view(term->grid, pos->row);
     wchar_t c = r->cells[pos->col].wc;
 
-    while (c == CELL_MULT_COL_SPACER) {
+    while (c >= CELL_SPACER) {
         xassert(pos->col > 0);
         if (pos->col == 0)
             return;
@@ -268,7 +268,7 @@ find_word_boundary_left(struct terminal *term, struct coord *pos,
         const struct row *row = grid_row_in_view(term->grid, next_row);
 
         c = row->cells[next_col].wc;
-        while (c == CELL_MULT_COL_SPACER) {
+        while (c >= CELL_SPACER) {
             xassert(next_col > 0);
             if (--next_col < 0)
                 return;
@@ -306,7 +306,7 @@ find_word_boundary_right(struct terminal *term, struct coord *pos,
     const struct row *r = grid_row_in_view(term->grid, pos->row);
     wchar_t c = r->cells[pos->col].wc;
 
-    while (c == CELL_MULT_COL_SPACER) {
+    while (c >= CELL_SPACER) {
         xassert(pos->col > 0);
         if (pos->col == 0)
             return;
@@ -340,7 +340,7 @@ find_word_boundary_right(struct terminal *term, struct coord *pos,
         const struct row *row = grid_row_in_view(term->grid, next_row);
 
         c = row->cells[next_col].wc;
-        while (c == CELL_MULT_COL_SPACER) {
+        while (c >= CELL_SPACER) {
             if (++next_col >= term->cols) {
                 next_col = 0;
                 if (++next_row >= term->rows)
@@ -554,7 +554,7 @@ set_pivot_point_for_block_and_char_wise(struct terminal *term,
         const struct row *row = term->grid->rows[pivot_start->row & (term->grid->num_rows - 1)];
         const struct cell *cell = &row->cells[pivot_start->col];
 
-        if (cell->wc != CELL_MULT_COL_SPACER)
+        if (cell->wc < CELL_SPACER)
             break;
 
         /* Multi-column chars don’t cross rows */
@@ -579,7 +579,7 @@ set_pivot_point_for_block_and_char_wise(struct terminal *term,
             const struct row *row = term->grid->rows[pivot_end->row & (term->grid->num_rows - 1)];
             const wchar_t wc = row->cells[pivot_end->col].wc;
 
-            keep_going = wc == CELL_MULT_COL_SPACER;
+            keep_going = wc >= CELL_SPACER;
 
             if (pivot_end->col == 0) {
                 if (pivot_end->row - term->grid->view <= 0)
@@ -596,7 +596,7 @@ set_pivot_point_for_block_and_char_wise(struct terminal *term,
             const wchar_t wc = pivot_start->col < term->cols - 1
                 ? row->cells[pivot_start->col + 1].wc : 0;
 
-            keep_going = wc == CELL_MULT_COL_SPACER;
+            keep_going = wc >= CELL_SPACER;
 
             if (pivot_start->col >= term->cols - 1) {
                 if (pivot_start->row - term->grid->view >= term->rows - 1)
@@ -609,9 +609,9 @@ set_pivot_point_for_block_and_char_wise(struct terminal *term,
     }
 
     xassert(term->grid->rows[pivot_start->row & (term->grid->num_rows - 1)]->
-           cells[pivot_start->col].wc != CELL_MULT_COL_SPACER);
+           cells[pivot_start->col].wc < CELL_SPACER);
     xassert(term->grid->rows[pivot_end->row & (term->grid->num_rows - 1)]->
-           cells[pivot_end->col].wc != CELL_MULT_COL_SPACER);
+           cells[pivot_end->col].wc < CELL_SPACER);
 }
 
 void
@@ -743,17 +743,17 @@ selection_update(struct terminal *term, int col, int row)
         (new_start.row == new_end.row && new_start.col <= new_end.col))
     {
         while (new_start.col >= 1 &&
-               row_start->cells[new_start.col].wc == CELL_MULT_COL_SPACER)
+               row_start->cells[new_start.col].wc >= CELL_SPACER)
             new_start.col--;
         while (new_end.col < term->cols - 1 &&
-               row_end->cells[new_end.col + 1].wc == CELL_MULT_COL_SPACER)
+               row_end->cells[new_end.col + 1].wc >= CELL_SPACER)
             new_end.col++;
     } else {
         while (new_end.col >= 1 &&
-               row_end->cells[new_end.col].wc == CELL_MULT_COL_SPACER)
+               row_end->cells[new_end.col].wc >= CELL_SPACER)
             new_end.col--;
         while (new_start.col < term->cols - 1 &&
-               row_start->cells[new_start.col + 1].wc == CELL_MULT_COL_SPACER)
+               row_start->cells[new_start.col + 1].wc >= CELL_SPACER)
             new_start.col++;
     }
 

terminal.c

@@ -2764,12 +2764,12 @@ print_insert(struct terminal *term, int width)
 }
 
 static void
-print_spacer(struct terminal *term, int col)
+print_spacer(struct terminal *term, int col, int remaining)
 {
     struct row *row = term->grid->cur_row;
     struct cell *cell = &row->cells[col];
 
-    cell->wc = CELL_MULT_COL_SPACER;
+    cell->wc = CELL_SPACER + remaining;
     cell->attrs = term->vt.attrs;
     cell->attrs.clean = 0;
 }
@@ -2803,7 +2803,7 @@ term_print(struct terminal *term, wchar_t wc, int width)
         /* Multi-column character that doesn't fit on current line -
          * pad with spacers */
         for (size_t i = term->grid->cursor.point.col; i < term->cols; i++)
-            print_spacer(term, i);
+            print_spacer(term, i, 0);
 
         /* And force a line-wrap */
         term->grid->cursor.lcf = 1;
@@ -2826,7 +2826,7 @@ term_print(struct terminal *term, wchar_t wc, int width)
     /* Advance cursor the 'additional' columns while dirty:ing the cells */
     for (int i = 1; i < width && term->grid->cursor.point.col < term->cols - 1; i++) {
         term->grid->cursor.point.col++;
-        print_spacer(term, term->grid->cursor.point.col);
+        print_spacer(term, term->grid->cursor.point.col, width - i);
     }
 
     /* Advance cursor */

terminal.h

@@ -48,7 +48,7 @@ static_assert(sizeof(struct attributes) == 8, "VT attribute struct too large");
 
 #define CELL_COMB_CHARS_LO    0x40000000ul
 #define CELL_COMB_CHARS_HI    0x400ffffful
-#define CELL_MULT_COL_SPACER  0x40100000ul
+#define CELL_SPACER           0x40100000ul
 
 struct cell {
     wchar_t wc;

vt.c

@@ -569,7 +569,7 @@ action_utf8_print(struct terminal *term, wchar_t wc)
         if (!term->grid->cursor.lcf)
             base_col--;
 
-        while (row->cells[base_col].wc == CELL_MULT_COL_SPACER && base_col > 0)
+        while (row->cells[base_col].wc >= CELL_SPACER && base_col > 0)
             base_col--;
 
         xassert(base_col >= 0 && base_col < term->cols);