From f78a0629507cfdb47671ad57185d2f4998015487 Mon Sep 17 00:00:00 2001
From: Jehan <jehan@girinstud.io>
Date: Wed, 29 Oct 2025 20:13:17 +0100
Subject: [PATCH] app, pdb: fix gimp_drawable_get_thumbnail() on high-bit depth
 drawable.

This bug had several causes:

* gimp_drawable_get_thumbnail_data() is pretty crappy as it just returns
  dimensions and bpp. You get no real format information.
* When using it to create a GdkPixbuf, which seems like the most common
  usage, only sRGB (with or without alpha) in 8-bit is supported by
  GdkPixbuf.

So I'm just making sure that private _gimp_drawable_thumbnail() PDB proc
is only returning 8-bit sRGB(A) data. For thumbnailing, this is probably
fine anyway.

Fixes when calling gimp_drawable_get_thumbnail() on an item from a
high-bit depth image:

> LibGimp-CRITICAL **: 20:12:21.028: file ../../../../../../../dev/src/gimp/libgimp/gimppixbuf.c: line 112 (_gimp_pixbuf_from_data): should not be reached
---
 app/pdb/drawable-cmds.c | 40 ++++++++++++++++++++++++++++++-----
 pdb/groups/drawable.pdb | 46 ++++++++++++++++++++++++++++++++++-------
 2 files changed, 73 insertions(+), 13 deletions(-)

diff --git a/app/pdb/drawable-cmds.c b/app/pdb/drawable-cmds.c
index 67f86bf8d4..a702feba1a 100644
--- a/app/pdb/drawable-cmds.c
+++ b/app/pdb/drawable-cmds.c
@@ -988,11 +988,41 @@ drawable_thumbnail_invoker (GimpProcedure         *procedure,
 
       if (buf)
         {
-          actual_width         = gimp_temp_buf_get_width  (buf);
-          actual_height        = gimp_temp_buf_get_height (buf);
-          bpp                  = babl_format_get_bytes_per_pixel (gimp_temp_buf_get_format (buf));
-          thumbnail_data       = g_bytes_new (gimp_temp_buf_get_data (buf),
-                                              gimp_temp_buf_get_data_size (buf));
+          const Babl *format      = gimp_temp_buf_get_format (buf);
+          const Babl *rgb_format  = babl_format ("R'G'B' u8");
+          const Babl *rgba_format = babl_format ("R'G'B'A u8");
+          const Babl *fish        = NULL;
+
+          if (babl_format_has_alpha (format) && format != rgba_format)
+            {
+              fish   = babl_fish (format, rgba_format);
+              format = rgba_format;
+            }
+          else if (! babl_format_has_alpha (format) && format != rgb_format)
+            {
+              fish   = babl_fish (format, rgb_format);
+              format = rgb_format;
+            }
+
+          actual_width  = gimp_temp_buf_get_width  (buf);
+          actual_height = gimp_temp_buf_get_height (buf);
+          bpp           = babl_format_get_bytes_per_pixel (format);
+          if (fish)
+            {
+              guchar *data;
+              gint    data_size = bpp * actual_width * actual_height;
+
+              data = g_malloc (data_size);
+              babl_process (fish, gimp_temp_buf_get_data (buf), data, actual_width * actual_height);
+
+              thumbnail_data = g_bytes_new (data, data_size);
+              g_free (data);
+            }
+          else
+            {
+              thumbnail_data = g_bytes_new (gimp_temp_buf_get_data (buf),
+                                            gimp_temp_buf_get_data_size (buf));
+            }
 
           gimp_temp_buf_unref (buf);
         }
diff --git a/pdb/groups/drawable.pdb b/pdb/groups/drawable.pdb
index bfbc2a166a..f71921d6fd 100644
--- a/pdb/groups/drawable.pdb
+++ b/pdb/groups/drawable.pdb
@@ -959,9 +959,9 @@ HELP
 	  desc => 'The previews height' },
 	{ name => 'bpp', type => 'int32',
 	  desc => 'The previews bpp' },
-  { name => 'thumbnail_data', type => 'bytes',
-    desc => 'The thumbnail data', }
-    );
+        { name => 'thumbnail_data', type => 'bytes',
+          desc => 'The thumbnail data', }
+          );
 
     %invoke = (
 	code => <<'CODE'
@@ -991,11 +991,41 @@ HELP
 
   if (buf)
     {
-      actual_width         = gimp_temp_buf_get_width  (buf);
-      actual_height        = gimp_temp_buf_get_height (buf);
-      bpp                  = babl_format_get_bytes_per_pixel (gimp_temp_buf_get_format (buf));
-      thumbnail_data       = g_bytes_new (gimp_temp_buf_get_data (buf),
-                                          gimp_temp_buf_get_data_size (buf));
+      const Babl *format      = gimp_temp_buf_get_format (buf);
+      const Babl *rgb_format  = babl_format ("R'G'B' u8");
+      const Babl *rgba_format = babl_format ("R'G'B'A u8");
+      const Babl *fish        = NULL;
+
+      if (babl_format_has_alpha (format) && format != rgba_format)
+        {
+          fish   = babl_fish (format, rgba_format);
+          format = rgba_format;
+        }
+      else if (! babl_format_has_alpha (format) && format != rgb_format)
+        {
+          fish   = babl_fish (format, rgb_format);
+          format = rgb_format;
+        }
+
+      actual_width  = gimp_temp_buf_get_width  (buf);
+      actual_height = gimp_temp_buf_get_height (buf);
+      bpp           = babl_format_get_bytes_per_pixel (format);
+      if (fish)
+        {
+          guchar *data;
+          gint    data_size = bpp * actual_width * actual_height;
+
+          data = g_malloc (data_size);
+          babl_process (fish, gimp_temp_buf_get_data (buf), data, actual_width * actual_height);
+
+          thumbnail_data = g_bytes_new (data, data_size);
+          g_free (data);
+        }
+      else
+        {
+          thumbnail_data = g_bytes_new (gimp_temp_buf_get_data (buf),
+                                        gimp_temp_buf_get_data_size (buf));
+        }
 
       gimp_temp_buf_unref (buf);
     }