sixel: if the client has specified a size, do not change that

We used to auto-resize images to always be a multiple of 6.

This is incorrect. The client may, for example, have specified a size
to align the image to a cell boundary, which may not be a multiple of
6.

Furthermore, in e.g. Jexer, which splits up an image into stripes,
that the next image would "overwrite" the previous one. Since the next
image was started on a cell row that the previous image had overflowed
into.

CHANGELOG.md

@@ -63,7 +63,9 @@
   a `;`.
 * Palette re-use in sixel images. Previously, the palette was reset
   after each image.
-
+* Do not auto-resize a sixel image for which the cllent has specified
+  a size. This fixes an issue where an image would incorrectly
+  overflow into the cell row beneath.
 
 ### Security
 

sixel.c

@@ -41,6 +41,7 @@ sixel_init(struct terminal *term)
     term->sixel.image.data = malloc(1 * 6 * sizeof(term->sixel.image.data[0]));
     term->sixel.image.width = 1;
     term->sixel.image.height = 6;
+    term->sixel.image.autosize = true;
 
     if (term->sixel.palette == NULL) {
         term->sixel.palette = calloc(
@@ -212,6 +213,9 @@ max_height(const struct terminal *term)
 static bool
 resize(struct terminal *term, int new_width, int new_height)
 {
+    if (!term->sixel.image.autosize)
+        return false;
+
     LOG_DBG("resizing image: %dx%d -> %dx%d",
             term->sixel.image.width, term->sixel.image.height,
             new_width, new_height);
@@ -220,6 +224,11 @@ resize(struct terminal *term, int new_width, int new_height)
     const int old_width = term->sixel.image.width;
     const int old_height = term->sixel.image.height;
 
+    int alloc_new_width = new_width;
+    int alloc_new_height = (new_height + 6 - 1) / 6 * 6;
+    assert(alloc_new_height >= new_height);
+    assert(alloc_new_height - new_height < 6);
+
     assert(new_width >= old_width);
     assert(new_height >= old_height);
 
@@ -229,7 +238,7 @@ resize(struct terminal *term, int new_width, int new_height)
         /* Width (and thus stride) is the same, so we can simply
          * re-alloc the existing buffer */
 
-        new_data = realloc(old_data, new_width * new_height * sizeof(uint32_t));
+        new_data = realloc(old_data, alloc_new_width * alloc_new_height * sizeof(uint32_t));
         if (new_data == NULL) {
             LOG_ERRNO("failed to reallocate sixel image buffer");
             return false;
@@ -240,7 +249,7 @@ resize(struct terminal *term, int new_width, int new_height)
     } else {
         /* Width (and thus stride) change - need to allocate a new buffer */
         assert(new_width > old_width);
-        new_data = malloc(new_width * new_height * sizeof(uint32_t));
+        new_data = malloc(alloc_new_width * alloc_new_height * sizeof(uint32_t));
 
         /* Copy old rows, and initialize new columns to background color */
         for (int r = 0; r < old_height; r++) {
@@ -278,7 +287,7 @@ sixel_add(struct terminal *term, uint32_t color, uint8_t sixel)
     }
 
     if (term->sixel.pos.col >= term->sixel.image.width ||
-        term->sixel.pos.row * 6 + 5 >= term->sixel.image.height)
+        term->sixel.pos.row * 6 + 5 >= (term->sixel.image.height + 6 - 1) / 6 * 6)
     {
         int width = max(
             term->sixel.image.width,
@@ -288,7 +297,8 @@ sixel_add(struct terminal *term, uint32_t color, uint8_t sixel)
             term->sixel.image.height,
             (term->sixel.pos.row + 1) * 6);
 
-        resize(term, width, height);
+        if (!resize(term, width, height))
+            return;
     }
 
     for (int i = 0; i < 6; i++, sixel >>= 1) {
@@ -389,7 +399,8 @@ decgra(struct terminal *term, uint8_t c)
         if (ph >= term->sixel.image.height && pv >= term->sixel.image.width &&
             ph <= max_height(term) && pv <= max_width(term))
         {
-            resize(term, ph, pv);
+            if (resize(term, ph, pv))
+                term->sixel.image.autosize = false;
         }
 
         term->sixel.state = SIXEL_DECSIXEL;

terminal.h

@@ -416,6 +416,7 @@ struct terminal {
             uint32_t *data;  /* Raw image data, in ARGB */
             int width;       /* Image width, in pixels */
             int height;      /* Image height, in pixels */
+            bool autosize;
         } image;
 
         unsigned params[5];  /* Collected parmaeters, for RASTER, COLOR_SPEC */