From c558e4151788fc1ebce34a29e4516471cf3e561d Mon Sep 17 00:00:00 2001
From: Jehan <jehan@girinstud.io>
Date: Fri, 21 Nov 2025 19:19:08 +0100
Subject: [PATCH] libgimpwidgets: update color area correctly when updating
 color.

Since we don't necessarily re-render the color area when the color
change, let's store the actually rendered color, additionally to the
supposedly rendered color. Otherwise when changing the color by very
small increments, small enough that the color is always perceptually
identical to the previous color, we never re-render the widget, even
when the rendered color is now quite different. Indeed the "identical
color" algorithm, based on CIE2000 distance, is not transitive.

Additionally I do not check for perceptual identity in
GimpColorSelection anymore, because we also check for this in the
GimpColorArea. Better always having the right color set in the area.

This was raised in #11339 (even though the initial issue was about the
hexadecimal field).
---
 libgimpwidgets/gimpcolorarea.c      |  9 ++++++-
 libgimpwidgets/gimpcolorselection.c | 40 ++++++++---------------------
 2 files changed, 18 insertions(+), 31 deletions(-)

diff --git a/libgimpwidgets/gimpcolorarea.c b/libgimpwidgets/gimpcolorarea.c
index dcb4e49d4e..215bd57bb0 100644
--- a/libgimpwidgets/gimpcolorarea.c
+++ b/libgimpwidgets/gimpcolorarea.c
@@ -80,6 +80,7 @@ struct _GimpColorArea
 
   GimpColorAreaType   type;
   GeglColor          *color;
+  GeglColor          *rendered;
   guint               draw_border  : 1;
   guint               needs_render : 1;
 
@@ -237,6 +238,7 @@ gimp_color_area_init (GimpColorArea *area)
   area->rowstride   = 0;
   area->draw_border = FALSE;
   area->color       = gegl_color_new ("black");
+  area->rendered    = NULL;
 
   gtk_drag_dest_set (GTK_WIDGET (area),
                      GTK_DEST_DEFAULT_HIGHLIGHT |
@@ -267,6 +269,7 @@ gimp_color_area_finalize (GObject *object)
 
   g_clear_pointer (&area->buf, g_free);
   g_clear_object (&area->color);
+  g_clear_object (&area->rendered);
 
   G_OBJECT_CLASS (parent_class)->finalize (object);
 }
@@ -528,7 +531,8 @@ gimp_color_area_set_color (GimpColorArea *area,
   g_return_if_fail (GIMP_IS_COLOR_AREA (area));
   g_return_if_fail (GEGL_IS_COLOR (color));
 
-  if (! gimp_color_is_perceptually_identical (area->color, color))
+  if (! area->rendered ||
+      ! gimp_color_is_perceptually_identical (area->rendered, color))
     {
       area->needs_render = TRUE;
       gtk_widget_queue_draw (GTK_WIDGET (area));
@@ -741,6 +745,9 @@ gimp_color_area_render_buf (GtkWidget         *widget,
   guchar        *p;
   gdouble        frac;
 
+  g_clear_object (&area->rendered);
+  area->rendered = gegl_color_duplicate (color);
+
   switch (type)
     {
     case GIMP_COLOR_AREA_FLAT:
diff --git a/libgimpwidgets/gimpcolorselection.c b/libgimpwidgets/gimpcolorselection.c
index de5b2c698d..42c2cb229c 100644
--- a/libgimpwidgets/gimpcolorselection.c
+++ b/libgimpwidgets/gimpcolorselection.c
@@ -440,23 +440,14 @@ void
 gimp_color_selection_set_color (GimpColorSelection *selection,
                                 GeglColor          *color)
 {
-  GeglColor  *old_color;
-  UpdateType  update;
-
   g_return_if_fail (GIMP_IS_COLOR_SELECTION (selection));
   g_return_if_fail (GEGL_IS_COLOR (color));
 
-  old_color = selection->color;
+  g_object_unref (selection->color);
   selection->color = gegl_color_duplicate (color);
 
-  update = UPDATE_ALL;
-  if (gimp_color_is_perceptually_identical (color, old_color))
-    update &= ~UPDATE_COLOR;
-
-  gimp_color_selection_update (selection, update);
+  gimp_color_selection_update (selection, UPDATE_ALL);
   gimp_color_selection_color_changed (selection);
-
-  g_object_unref (old_color);
 }
 
 /**
@@ -676,20 +667,15 @@ gimp_color_selection_notebook_changed (GimpColorSelector  *selector,
                                        GeglColor          *color,
                                        GimpColorSelection *selection)
 {
-  GeglColor  *old_color;
-  UpdateType  update;
+  UpdateType update;
 
-  old_color = selection->color;
+  update = UPDATE_SCALES | UPDATE_ENTRY | UPDATE_COLOR;
+
+  g_object_unref (selection->color);
   selection->color = gegl_color_duplicate (color);
 
-  update = UPDATE_SCALES | UPDATE_ENTRY;
-  if (! gimp_color_is_perceptually_identical (color, old_color))
-    update |= UPDATE_COLOR;
-
   gimp_color_selection_update (selection, update);
   gimp_color_selection_color_changed (selection);
-
-  g_object_unref (old_color);
 }
 
 static void
@@ -697,21 +683,15 @@ gimp_color_selection_scales_changed (GimpColorSelector  *selector,
                                      GeglColor          *color,
                                      GimpColorSelection *selection)
 {
-  UpdateType  update;
-  GeglColor  *old_color;
+  UpdateType update;
 
-  old_color = selection->color;
+  update = UPDATE_ENTRY | UPDATE_NOTEBOOK | UPDATE_COLOR;
+
+  g_object_unref (selection->color);
   selection->color = gegl_color_duplicate (color);
 
-  update = UPDATE_ENTRY | UPDATE_NOTEBOOK;
-  if (! gimp_color_is_perceptually_identical (color, old_color))
-    update |= UPDATE_COLOR;
-
   gimp_color_selection_update (selection, update);
-
   gimp_color_selection_color_changed (selection);
-
-  g_object_unref (old_color);
 }
 
 static void