Use compact image references in grid cells

grid.c

@@ -80,7 +80,7 @@ grid_entry_image(struct grid_line *gl, struct grid_cell_entry *gce)
 	gee = &gl->extddata[gce->offset];
 	if (~gee->flags & GRID_FLAG_IMAGE)
 		return (0);
-	return (gee->image_id);
+	return (image_get_id_by_grid_id(gee->image_id));
 }
 #endif
 
@@ -211,7 +211,7 @@ grid_extended_cell(struct grid_line *gl, struct grid_cell_entry *gce,
 	gee->us = gc->us;
 	gee->link = gc->link;
 #ifdef ENABLE_IMAGES
-	gee->image_id = gc->image_id;
+	gee->image_id = image_get_grid_id(gc->image_id);
 	gee->image_x = gc->image_x;
 	gee->image_y = gc->image_y;
 #endif
@@ -684,7 +684,7 @@ grid_get_cell1(struct grid_line *gl, u_int px, struct grid_cell *gc)
 			gc->us = gee->us;
 			gc->link = gee->link;
 #ifdef ENABLE_IMAGES
-			gc->image_id = gee->image_id;
+			gc->image_id = image_get_id_by_grid_id(gee->image_id);
 			gc->image_x = gee->image_x;
 			gc->image_y = gee->image_y;
 #endif

image.c

@@ -45,6 +45,7 @@ struct image_cell {
 /* Immutable image data and cell geometry. */
 struct image {
 	u_int			 id;
+	u_short			 grid_id;
 	u_int			 references;
 	u_int			 width;
 	u_int			 height;
@@ -78,6 +79,8 @@ struct image_rectangle {
 
 static struct images	images = RB_INITIALIZER(&images);
 static u_int		image_next_id;
+static u_short		image_next_grid_id;
+static struct image	*image_grid_ids[USHRT_MAX + 1];
 
 #define IMAGE_BACKEND_GRAPHICAL 0x1
 #define IMAGE_BACKEND_SCROLLS   0x2
@@ -345,6 +348,7 @@ image_create(u_int width, u_int height, u_int canvas_width,
     u_int canvas_height, u_int sx, u_int sy, u_char *pixels)
 {
 	struct image	*im;
+	u_int		 i;
 
 	if (width == 0 || height == 0 || canvas_width < width ||
 	    canvas_height < height || sx == 0 || sy == 0 || pixels == NULL)
@@ -353,6 +357,16 @@ image_create(u_int width, u_int height, u_int canvas_width,
 		return (NULL);
 	if ((uint64_t)sx * sy > SIZE_MAX / sizeof *im->cells)
 		return (NULL);
+	if (sx > USHRT_MAX || sy > USHRT_MAX)
+		return (NULL);
+	for (i = 0; i < USHRT_MAX; i++) {
+		if (++image_next_grid_id == 0)
+			image_next_grid_id++;
+		if (image_grid_ids[image_next_grid_id] == NULL)
+			break;
+	}
+	if (i == USHRT_MAX)
+		return (NULL);
 
 	im = xcalloc(1, sizeof *im);
 	do {
@@ -362,6 +376,7 @@ image_create(u_int width, u_int height, u_int canvas_width,
 	} while (image_find(im->id) != NULL);
 
 	im->references = 1;
+	im->grid_id = image_next_grid_id;
 	im->width = width;
 	im->height = height;
 	im->canvas_width = canvas_width;
@@ -373,12 +388,33 @@ image_create(u_int width, u_int height, u_int canvas_width,
 	im->pixels = pixels;
 
 	RB_INSERT(images, &images, im);
+	image_grid_ids[im->grid_id] = im;
 	log_debug("%s: image %u is %ux%u pixels on %ux%u canvas, "
 	    "%ux%u cells", __func__, im->id, width, height, canvas_width,
 	    canvas_height, sx, sy);
 	return (im);
 }
 
+u_short
+image_get_grid_id(u_int id)
+{
+	struct image	*im = image_find(id);
+
+	if (im == NULL)
+		return (0);
+	return (im->grid_id);
+}
+
+u_int
+image_get_id_by_grid_id(u_short grid_id)
+{
+	struct image	*im;
+
+	if (grid_id == 0 || (im = image_grid_ids[grid_id]) == NULL)
+		return (0);
+	return (im->id);
+}
+
 void
 image_ref(u_int id)
 {
@@ -403,6 +439,7 @@ image_free(u_int id)
 
 	log_debug("%s: freeing image %u", __func__, id);
 	RB_REMOVE(images, &images, im);
+	image_grid_ids[im->grid_id] = NULL;
 	free(im->pixels);
 	if (im->sixel != NULL)
 		sixel_free(im->sixel);

tmux.h

@@ -887,9 +887,9 @@ struct grid_extd_entry {
 	int			us;
 	u_int			link;
 #ifdef ENABLE_IMAGES
-	u_int			image_id;
-	u_int			image_x;
-	u_int			image_y;
+	u_short			image_id;
+	u_short			image_x;
+	u_short			image_y;
 #endif
 } __packed;
 
@@ -4242,6 +4242,8 @@ struct image	*image_create(u_int, u_int, u_int, u_int, u_int, u_int,
 		     u_char *);
 struct image	*image_find(u_int);
 u_int		 image_get_id(const struct image *);
+u_short		 image_get_grid_id(u_int);
+u_int		 image_get_id_by_grid_id(u_short);
 void		 image_get_dimensions(const struct image *, u_int *, u_int *);
 void		 image_get_canvas_dimensions(const struct image *, u_int *, u_int *);
 void		 image_get_cell_dimensions(const struct image *, u_int *, u_int *);