term: print: write special value CELL_MULT_COL_SPACER to extra cells

When printing a multi-column character, write CELL_MULT_COL_SPACER
instead of '0' to both padding cells (when character doesn't fit at
the end of the line), and to the cells following the actual character.

render.c

@@ -438,7 +438,7 @@ 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->attrs.conceal)
+    if (cell->wc == 0 || cell->wc == CELL_MULT_COL_SPACER || cell->attrs.conceal)
         goto draw_cursor;
 
     pixman_image_t *clr_pix = pixman_image_create_solid_fill(&fg);

selection.c

@@ -134,9 +134,9 @@ foreach_selected_normal(
              c <= (r == end_row ? end_col : term->cols - 1);
              c++)
         {
+            if (row->cells[c].wc == CELL_MULT_COL_SPACER)
+                continue;
             cb(term, row, &row->cells[c], c, data);
-            c += max(1, wcwidth(row->cells[c].wc)) - 1;
-            assert(c < term->cols);
         }
 
         start_col = 0;
@@ -168,9 +168,9 @@ foreach_selected_block(
         assert(row != NULL);
 
         for (int c = top_left.col; c <= bottom_right.col; c++) {
+            if (row->cells[c].wc == CELL_MULT_COL_SPACER)
+                continue;
             cb(term, row, &row->cells[c], c, data);
-            c += max(1, wcwidth(row->cells[c].wc)) - 1;
-            assert(c < term->cols);
         }
     }
 }

terminal.c

@@ -2397,18 +2397,15 @@ term_print(struct terminal *term, wchar_t wc, int width)
         term->grid->cursor.point.col + width > term->cols)
     {
         /* Multi-column character that doesn't fit on current line -
-         * force a line wrap */
-        term->grid->cursor.lcf = 1;
+         * pad with spacers */
+        for (size_t i = term->grid->cursor.point.col; i < term->cols; i++) {
+            struct cell *cell = &term->grid->cur_row->cells[i];
+            cell->wc = CELL_MULT_COL_SPACER;
+            cell->attrs.clean = 0;
+        }
 
-        /*
-         * TODO: should we insert place holder values in the remaining
-         * cells?  This would allow e.g. text extraction to simply
-         * skip these, instead of trying to recognize a sequence of
-         * empty cells at the end of the line followed by a
-         * multi-column character...
-         *
-         * Might also make text reflow easier, or even more correct.
-         */
+        /* And force a line-wrap */
+        term->grid->cursor.lcf = 1;
     }
 
     print_linewrap(term);
@@ -2431,7 +2428,7 @@ term_print(struct terminal *term, wchar_t wc, int width)
         term->grid->cursor.point.col++;
 
         struct cell *cell = &row->cells[term->grid->cursor.point.col];
-        cell->wc = 0;
+        cell->wc = CELL_MULT_COL_SPACER;
         cell->attrs.clean = 0;
     }
 

terminal.h

@@ -50,6 +50,8 @@ static_assert(sizeof(struct attributes) == 8, "bad size");
 
 #define CELL_COMB_CHARS_LO    0x40000000ul
 #define CELL_COMB_CHARS_HI    0x400ffffful
+#define CELL_MULT_COL_SPACER  0x40100000ul
+
 struct cell {
     wchar_t wc;
     struct attributes attrs;