sixel: improve handling of images when reflowing the grids

Update the sixels' 'row' attribute when re-flowing a grid, to ensure
it is rendered at the correct place.

This should work in most cases, but will break when the cell size has
changed (e.g. font size increase/decrease, or a DPI change).

This patch also moves the sixel image list from the terminal struct
into the grid struct. The sixels are per-grid after all.

CHANGELOG.md

@@ -17,6 +17,7 @@
 ### Fixed
 * Window size doubling when moving window between outputs with
   different scaling factors (https://codeberg.org/dnkl/foot/issues/3).
+* Sixel images moved or deleted on window resize.
 
 ### Security
 

csi.c

@@ -1143,11 +1143,9 @@ csi_dispatch(struct terminal *term, uint8_t final)
                         tll_free(term->alt.scroll_damage);
 
                         /* Delete all sixel images on the alt screen */
-                        tll_foreach(term->sixel_images, it) {
-                            if (it->item.grid == &term->alt) {
-                                sixel_destroy(&it->item);
-                                tll_remove(term->sixel_images, it);
-                            }
+                        tll_foreach(term->alt.sixel_images, it) {
+                            sixel_destroy(&it->item);
+                            tll_remove(term->alt.sixel_images, it);
                         }
 
                         term_damage_all(term);

grid.c

@@ -6,6 +6,7 @@
 #define LOG_MODULE "grid"
 #define LOG_ENABLE_DBG 0
 #include "log.h"
+#include "sixel.h"
 
 #define max(x, y) ((x) > (y) ? (x) : (y))
 
@@ -76,6 +77,8 @@ grid_reflow(struct grid *grid, int new_rows, int new_cols,
      * at the output that is *oldest* */
     int offset = grid->offset + old_screen_rows;
 
+    tll(struct sixel) new_sixels = tll_init();
+
     /*
      * Walk the old grid
      */
@@ -86,6 +89,28 @@ grid_reflow(struct grid *grid, int new_rows, int new_cols,
         if (old_row == NULL)
             continue;
 
+        /*
+         * Update 'row' in all sixels that *begin* at current row
+         *
+         * Since we might end up pushing the sixel down, we can't
+         * simply update the row inline - we'd then end up pushing the
+         * sixel down again, when we reach the next 'old'
+         * row. Instead, copy the sixel (with 'row' updated), to a
+         * temporary list and remove the original sixel.
+         *
+         * After we've reflowed the grid we'll move the sixels back to
+         * the "real" sixel list.
+         */
+        tll_foreach(grid->sixel_images, it) {
+            if (it->item.pos.row == ((offset + r) & (old_rows - 1))) {
+                struct sixel six = it->item;
+                six.pos.row = new_row_idx;
+
+                tll_push_back(new_sixels, six);
+                tll_remove(grid->sixel_images, it);
+            }
+        }
+
         /*
          * Keep track of empty cells. If the old line ends with a
          * string of empty cells, we don't need to, nor do we want to,
@@ -191,5 +216,15 @@ grid_reflow(struct grid *grid, int new_rows, int new_cols,
     grid->num_rows = new_rows;
     grid->num_cols = new_cols;
 
+    /* Destroy any non-moved sixels */
+    tll_foreach(grid->sixel_images, it)
+        sixel_destroy(&it->item);
+    tll_free(grid->sixel_images);
+
+    /* Move updated sixels back */
+    tll_foreach(new_sixels, it)
+        tll_push_back(grid->sixel_images, it->item);
+    tll_free(new_sixels);
+
     return new_row_idx;
 }

render.c

@@ -531,9 +531,6 @@ static void
 render_sixel(struct terminal *term, pixman_image_t *pix,
              const struct sixel *sixel)
 {
-    if (sixel->grid != term->grid)
-        return;
-
     int view_end = (term->grid->view + term->rows - 1) & (term->grid->num_rows - 1);
     int first_visible_row = -1;
 
@@ -599,7 +596,7 @@ render_sixel(struct terminal *term, pixman_image_t *pix,
 static void
 render_sixel_images(struct terminal *term, pixman_image_t *pix)
 {
-    tll_foreach(term->sixel_images, it)
+    tll_foreach(term->grid->sixel_images, it)
         render_sixel(term, pix, &it->item);
 }
 

sixel.c

@@ -76,22 +76,19 @@ sixel_erase(struct terminal *term, struct sixel *sixel)
 void
 sixel_delete_at_row(struct terminal *term, int _row)
 {
-    if (likely(tll_length(term->sixel_images) == 0))
+    if (likely(tll_length(term->grid->sixel_images) == 0))
         return;
 
-    tll_foreach(term->sixel_images, it) {
+    tll_foreach(term->grid->sixel_images, it) {
         struct sixel *six = &it->item;
 
-        if (six->grid != term->grid)
-            continue;
-
         const int row = (term->grid->offset + _row) & (term->grid->num_rows - 1);
         const int six_start = six->pos.row;
         const int six_end = six_start + six->rows - 1;
 
         if (row >= six_start && row <= six_end) {
             sixel_erase(term, six);
-            tll_remove(term->sixel_images, it);
+            tll_remove(term->grid->sixel_images, it);
         }
     }
 }
@@ -101,18 +98,15 @@ sixel_delete_in_range(struct terminal *term, int _start, int _end)
 {
     assert(_end >= _start);
 
-    if (likely(tll_length(term->sixel_images) == 0))
+    if (likely(tll_length(term->grid->sixel_images) == 0))
         return;
 
     if (_start == _end)
         return sixel_delete_at_row(term, _start);
 
-    tll_foreach(term->sixel_images, it) {
+    tll_foreach(term->grid->sixel_images, it) {
         struct sixel *six = &it->item;
 
-        if (six->grid != term->grid)
-            continue;
-
         const int start = (term->grid->offset + _start) & (term->grid->num_rows - 1);
         const int end = start + (_end - _start);
         const int six_start = six->pos.row;
@@ -123,7 +117,7 @@ sixel_delete_in_range(struct terminal *term, int _start, int _end)
             (start >= six_start && end <= six_end))      /* Fully within sixel range */
         {
             sixel_erase(term, six);
-            tll_remove(term->sixel_images, it);
+            tll_remove(term->grid->sixel_images, it);
         }
     }
 }
@@ -147,7 +141,6 @@ sixel_unhook(struct terminal *term)
         .width = term->sixel.image.width,
         .height = term->sixel.image.height,
         .rows = (term->sixel.image.height + term->cell_height - 1) / term->cell_height,
-        .grid = term->grid,
         .pos = (struct coord){
             term->cursor.point.col,
             (term->grid->offset + term->cursor.point.row) & (term->grid->num_rows - 1)},
@@ -172,7 +165,7 @@ sixel_unhook(struct terminal *term)
     term_formfeed(term);
     render_refresh(term);
 
-    tll_push_back(term->sixel_images, image);
+    tll_push_back(term->grid->sixel_images, image);
 }
 
 static unsigned

terminal.c

@@ -721,8 +721,8 @@ term_init(const struct config *conf, struct fdm *fdm, struct wayland *wayl,
             .start = {-1, -1},
             .end = {-1, -1},
         },
-        .normal = {.damage = tll_init(), .scroll_damage = tll_init()},
-        .alt = {.damage = tll_init(), .scroll_damage = tll_init()},
+        .normal = {.damage = tll_init(), .scroll_damage = tll_init(), .sixel_images = tll_init()},
+        .alt = {.damage = tll_init(), .scroll_damage = tll_init(), .sixel_images = tll_init()},
         .grid = &term->normal,
         .meta = {
             .esc_prefix = true,
@@ -747,7 +747,6 @@ term_init(const struct config *conf, struct fdm *fdm, struct wayland *wayl,
         .sixel = {
             .palette_size = SIXEL_MAX_COLORS,
         },
-        .sixel_images = tll_init(),
         .hold_at_exit = conf->hold_at_exit,
         .shutdown_cb = shutdown_cb,
         .shutdown_data = shutdown_data,
@@ -978,9 +977,12 @@ term_destroy(struct terminal *term)
     tll_free(term->ptmx_buffer);
     tll_free(term->tab_stops);
 
-    tll_foreach(term->sixel_images, it)
+    tll_foreach(term->normal.sixel_images, it)
         sixel_destroy(&it->item);
-    tll_free(term->sixel_images);
+    tll_free(term->normal.sixel_images);
+    tll_foreach(term->alt.sixel_images, it)
+        sixel_destroy(&it->item);
+    tll_free(term->alt.sixel_images);
 
     free(term->foot_exe);
     free(term->cwd);
@@ -1104,9 +1106,12 @@ term_reset(struct terminal *term, bool hard)
     term->meta.esc_prefix = true;
     term->meta.eight_bit = true;
 
-    tll_foreach(term->sixel_images, it)
+    tll_foreach(term->normal.sixel_images, it)
         sixel_destroy(&it->item);
-    tll_free(term->sixel_images);
+    tll_free(term->normal.sixel_images);
+    tll_foreach(term->alt.sixel_images, it)
+        sixel_destroy(&it->item);
+    tll_free(term->alt.sixel_images);
 
     if (!hard)
         return;

terminal.h

@@ -86,6 +86,15 @@ struct row {
     bool linebreak;
 };
 
+struct sixel {
+    void *data;
+    pixman_image_t *pix;
+    int width;
+    int height;
+    int rows;
+    struct coord pos;
+};
+
 struct grid {
     int num_rows;
     int num_cols;
@@ -97,6 +106,7 @@ struct grid {
 
     tll(struct damage) damage;
     tll(struct damage) scroll_damage;
+    tll(struct sixel) sixel_images;
 };
 
 struct vt_subparams {
@@ -175,16 +185,6 @@ struct ptmx_buffer {
     size_t idx;
 };
 
-struct sixel {
-    void *data;
-    pixman_image_t *pix;
-    int width;
-    int height;
-    int rows;
-    const struct grid *grid;
-    struct coord pos;
-};
-
 enum term_surface {
     TERM_SURF_NONE,
     TERM_SURF_GRID,
@@ -417,8 +417,6 @@ struct terminal {
         unsigned max_height;    /* Maximum image height, in pixels */
     } sixel;
 
-    tll(struct sixel) sixel_images;
-
     bool hold_at_exit;
     bool is_shutting_down;
     void (*shutdown_cb)(void *data, int exit_code);