From fbbecde2364457a1187501c23f5e1a2143616f7d Mon Sep 17 00:00:00 2001
From: Nicholas Marriott <nicholas.marriott@gmail.com>
Date: Tue, 13 Oct 2026 22:43:16 +0100
Subject: [PATCH] SIXEL image placement.

---
 image-grid.c  | 112 +++++++++++++++++++++++++++++++++++++++++++++++++-
 image-sixel.c |   9 ++--
 image.c       |  39 ++++++++++++++++++
 tmux-image.h  |   3 ++
 4 files changed, 157 insertions(+), 6 deletions(-)

diff --git a/image-grid.c b/image-grid.c
index 0873e9170..bf8e8bb38 100644
--- a/image-grid.c
+++ b/image-grid.c
@@ -196,7 +196,7 @@ image_grid_add(struct grid *gd, struct image *im, u_int x, u_int y,
 	}
 }
 
-/* Remove the covered part of each span, retaining either side. */
+/* Remove the covered part of a span. */
 static void
 image_line_remove(struct image_line *line, u_int x, u_int w)
 {
@@ -459,3 +459,113 @@ image_damage_screen(struct screen_write_ctx *ctx, u_int x, u_int y, u_int sx,
 	if (ctx->flags & SCREEN_WRITE_INPUT)
 		image_grid_remove(s->grid, x, s->grid->hsize + y, sx, sy);
 }
+
+/* Return whether an image cell has any visible pixels. */
+static int
+image_cell_has_visible_pixels(struct image *im, u_int x, u_int y)
+{
+	u_int		 px, py, sx, sy, xx, yy;
+	const u_char	*pixels;
+	size_t		 stride;
+
+	image_get_pixel_area(im, x, y, 1, 1, &px, &py, &sx, &sy);
+	if (sx == 0 || sy == 0)
+		return (0);
+	pixels = image_get_pixels(im, &stride, NULL);
+	for (yy = py; yy < py + sy; yy++) {
+		for (xx = px; xx < px + sx; xx++) {
+			if (pixels[yy * stride + xx * 4 + 3] != 0)
+				return (1);
+		}
+	}
+	return (0);
+}
+
+/* Attach the visible runs from one image row. */
+static void
+image_add_row(struct image_line *line, struct image_placement *plmt,
+    u_int cx, u_int src_y, u_int sx)
+{
+	struct image	*im = plmt->image;
+	u_int		 x, run;
+
+	for (x = 0; x < sx; x += run) {
+		if (!image_cell_has_visible_pixels(im, x, src_y)) {
+			run = 1;
+			continue;
+		}
+		for (run = 1; x + run < sx; run++) {
+			if (!image_cell_has_visible_pixels(im, x + run, src_y))
+				break;
+		}
+		image_span_add(line, plmt, cx + x, run, x, src_y);
+	}
+}
+
+/* Place a SIXEL image at the cursor. */
+void
+image_write(struct screen_write_ctx *ctx, struct image *im, u_int bg)
+{
+	struct screen		*s = ctx->s;
+	struct grid		*gd = s->grid;
+	struct image_placement	*plmt;
+	struct grid_line	*gl;
+	struct image_line	*line;
+	u_int			 cx = s->cx, cy = s->cy, y, sx, sy, lines;
+	u_int			 origin_y = 0, h_origin_y, region_height;
+	u_int			 remaining, n;
+
+	image_get_size_in_cells(im, &sx, &sy);
+	if (sx > screen_size_x(s) - cx)
+		sx = screen_size_x(s) - cx;
+	if (sx == 0)
+		return;
+
+	/* Scroll images that move the cursor. */
+	if (screen_size_y(s) - cy <= sy) {
+		lines = sy - (screen_size_y(s) - cy) + 1;
+		region_height = s->rlower - s->rupper + 1;
+
+		remaining = lines;
+		while (remaining > 0) {
+			if (remaining < region_height)
+				n = remaining;
+			else
+				n = region_height;
+			screen_write_scrollup(ctx, n, bg);
+			remaining -= n;
+		}
+
+		if (lines > cy) {
+			origin_y = lines - cy;
+			screen_write_cursormove(ctx, -1, 0, 0);
+		} else {
+			origin_y = 0;
+			screen_write_cursormove(ctx, -1, cy - lines, 0);
+		}
+		cy = s->cy;
+		sy -= origin_y;
+	}
+	plmt = image_placement_create(gd, im);
+
+	/* Attach scrolled image rows to the available history lines. */
+	h_origin_y = origin_y;
+	if (h_origin_y > gd->hsize)
+		h_origin_y = gd->hsize;
+	for (y = 0; y < h_origin_y; y++) {
+		gl = &gd->linedata[gd->hsize - h_origin_y + y];
+		line = image_line_get(gl);
+		image_add_row(line, plmt, cx, origin_y - h_origin_y + y, sx);
+	}
+
+	/* Attach visible image rows. */
+	for (y = 0; y < sy; y++) {
+		line = image_line_get(&gd->linedata[gd->hsize + cy + y]);
+		image_add_row(line, plmt, cx, origin_y + y, sx);
+	}
+
+	/* Schedule a redraw and advance the cursor past the image. */
+	image_store_prune(gd->images);
+	image_redraw_area(ctx, cx, cy, sx, sy);
+	screen_write_cursormove(ctx, 0, cy + sy, 0);
+}
diff --git a/image-sixel.c b/image-sixel.c
index 65de8ab20..c7fc56b3d 100644
--- a/image-sixel.c
+++ b/image-sixel.c
@@ -515,10 +515,10 @@ sixel_to_image(struct sixel_image *si)
 	    (uint64_t)sy * si->ypixel > UINT_MAX)
 		return (NULL);
 
-	pixels = xcalloc((size_t)si->x * si->y, 4);
+	pixels = xcalloc(si->x * si->y, 4);
 	for (y = 0; y < si->y; y++) {
 		for (x = 0; x < si->x; x++) {
-			pixel = pixels + ((size_t)y * si->x + x) * 4;
+			pixel = pixels + (y * si->x + x) * 4;
 
 			c = sixel_get_pixel(si, x, y);
 			if (c == 0) {
@@ -545,8 +545,7 @@ sixel_to_image(struct sixel_image *si)
 
 /* Write a SIXEL image. */
 void
-sixel_write(__unused struct screen_write_ctx *ctx, struct sixel_image *si,
-    __unused u_int bg)
+sixel_write(struct screen_write_ctx *ctx, struct sixel_image *si, u_int bg)
 {
 	struct image *im;
 
@@ -554,6 +553,6 @@ sixel_write(__unused struct screen_write_ctx *ctx, struct sixel_image *si,
 	sixel_free(si);
 	if (im == NULL)
 		return;
-	/* XXX image_write_sixel */
+	image_write(ctx, im, bg);
 	image_free(im);
 }
diff --git a/image.c b/image.c
index 47de935b9..5f7036612 100644
--- a/image.c
+++ b/image.c
@@ -302,3 +302,42 @@ image_size_in_cells(u_int w, u_int h, u_int xpixel, u_int ypixel, u_int *sx,
 	*sx = w / xpixel + (w % xpixel != 0);
 	*sy = h / ypixel + (h % ypixel != 0);
 }
+
+/* Find area covered by a rectangle of cells in pixels. */
+void
+image_get_pixel_area(struct image *im, u_int x, u_int y, u_int w, u_int h,
+    u_int *px, u_int *py, u_int *pw, u_int *ph)
+{
+	u_int	left, top, right, bottom;
+
+	*px = *py = *pw = *ph = 0;
+
+	if (im == NULL || x >= im->sx || y >= im->sy || w == 0 || h == 0)
+		return;
+	if (w > im->sx - x)
+		w = im->sx - x;
+	if (h > im->sy - y)
+		h = im->sy - y;
+
+	left = (uint64_t)x * im->canvas_width / im->sx;
+	top = (uint64_t)y * im->canvas_height / im->sy;
+	right = ((uint64_t)(x + w) * im->canvas_width + im->sx - 1) / im->sx;
+	bottom = ((uint64_t)(y + h) * im->canvas_height + im->sy - 1) / im->sy;
+
+	if (left >= im->width || top >= im->height)
+		*px = *py = 0;
+	else {
+		if (right <= left)
+			right = left + 1;
+		if (bottom <= top)
+			bottom = top + 1;
+		if (right > im->width)
+			right = im->width;
+		if (bottom > im->height)
+			bottom = im->height;
+		*px = left;
+		*py = top;
+		*pw = right - left;
+		*ph = bottom - top;
+	}
+}
diff --git a/tmux-image.h b/tmux-image.h
index 5211bf3f6..2ac55c649 100644
--- a/tmux-image.h
+++ b/tmux-image.h
@@ -72,6 +72,8 @@ void		 image_get_size_in_cells(struct image *, u_int *, u_int *);
 const u_char	*image_get_pixels(struct image *, size_t *, size_t *);
 void		 image_size_in_cells(u_int, u_int, u_int, u_int, u_int *,
 		     u_int *);
+void		 image_get_pixel_area(struct image *, u_int, u_int, u_int,
+		     u_int, u_int *, u_int *, u_int *, u_int *);
 
 /* image-grid.c */
 void		 image_grid_add(struct grid *, struct image *, u_int, u_int,
@@ -92,6 +94,7 @@ void		 image_redraw_all(struct screen_write_ctx *);
 void		 image_redraw_scroll(struct screen_write_ctx *);
 void		 image_damage_screen(struct screen_write_ctx *, u_int, u_int,
 		     u_int, u_int);
+void		 image_write(struct screen_write_ctx *, struct image *, u_int);
 
 /* image-sixel.c */
 #define SIXEL_COLOUR_REGISTERS 1024