From 4c15be6a566247d5743341ada68badaffc1a6a95 Mon Sep 17 00:00:00 2001
From: Jehan <jehan@girinstud.io>
Date: Sat, 28 Feb 2026 20:01:28 +0100
Subject: [PATCH] app: fix merging filters with negative top-left point.
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When merging filters whose rendering was expanding in negative
ccordinates, I realized that the drawable was not properly resized (it
was resized properly when the width/height increased, but not when the x
or y points became negative, even though this "cropped" part still
showed… until you saved and reloaded your XCF!).

The problem is that drawable buffers are always stored with (0, 0)
top-left and this was just confusing our existing code. So let's check
when trying to set a buffer with a non-(0, 0) origin, and update the
offset subsequently.

I hesitated with an alternative implementation which was to edit the
buffer applied to the drawable in gimp_drawable_merge_filters(). But I
figured this would be more future-proof for other similar cases, though
I hope I did not break any use case where this was actually considered a
normal case.
---
 app/core/gimpdrawable.c | 29 +++++++++++++++++++++++++----
 1 file changed, 25 insertions(+), 4 deletions(-)

diff --git a/app/core/gimpdrawable.c b/app/core/gimpdrawable.c
index 646c960af9..92d3da3577 100644
--- a/app/core/gimpdrawable.c
+++ b/app/core/gimpdrawable.c
@@ -1013,9 +1013,11 @@ gimp_drawable_real_set_buffer (GimpDrawable        *drawable,
                                GeglBuffer          *buffer,
                                const GeglRectangle *bounds)
 {
-  GimpItem   *item          = GIMP_ITEM (drawable);
-  const Babl *old_format    = NULL;
-  gint        old_has_alpha = -1;
+  GimpItem            *item          = GIMP_ITEM (drawable);
+  const Babl          *old_format    = NULL;
+  gint                 old_has_alpha = -1;
+  const GeglRectangle *extent        = gegl_buffer_get_extent (buffer);
+  gboolean             free_buffer   = FALSE;
 
   g_object_freeze_notify (G_OBJECT (drawable));
 
@@ -1031,6 +1033,22 @@ gimp_drawable_real_set_buffer (GimpDrawable        *drawable,
       old_has_alpha = gimp_drawable_has_alpha (drawable);
     }
 
+  if (extent->x != 0 || extent->y != 0)
+    {
+      /* Drawable buffers are always stored with a (0, 0) origin. When
+       * setting a buffer with a different origin, we will assume we
+       * instead want to update the offset a bit.
+       * This may happen for instance when merging filters which may
+       * render in negative coordinates.
+       */
+      buffer = g_object_new (GEGL_TYPE_BUFFER,
+                             "source",  buffer,
+                             "shift-x", extent->x,
+                             "shift-y", extent->y,
+                             NULL);
+      free_buffer = TRUE;
+    }
+
   g_set_object (&drawable->private->buffer, buffer);
 
   if (gimp_drawable_is_painting (drawable))
@@ -1043,7 +1061,7 @@ gimp_drawable_real_set_buffer (GimpDrawable        *drawable,
                    "buffer", gimp_drawable_get_buffer (drawable),
                    NULL);
 
-  gimp_item_set_offset (item, bounds->x, bounds->y);
+  gimp_item_set_offset (item, bounds->x + extent->x, bounds->y + extent->y);
   gimp_item_set_size (item,
                       bounds->width  ? bounds->width :
                                        gegl_buffer_get_width (buffer),
@@ -1061,6 +1079,9 @@ gimp_drawable_real_set_buffer (GimpDrawable        *drawable,
   g_object_notify (G_OBJECT (drawable), "buffer");
 
   g_object_thaw_notify (G_OBJECT (drawable));
+
+  if (free_buffer)
+    g_object_unref (buffer);
 }
 
 static GeglRectangle