[gimp] app: restore gradient when adding/removing stop on same blend-tool action

[N/A <ell src gnome org>]

commit 945ef0de25a863aa2d28e56b862c5325fcf3b9c6
Author: Ell <ell_se yahoo com>
Date:   Thu Nov 16 11:47:03 2017 -0500

    app: restore gradient when adding/removing stop on same blend-tool action
    
    When a single blend-tool action adds and removes the same gradient
    stop, restore the original gradient, rather than actually adding
    and removing the stop, so that the affected midpoint returns to its
    original state at the beginning of the action, rather than being
    reset (and, consequently, so that the redo stack isn't lost.)

 app/tools/gimpblendtool-editor.c |   89 +++++++++++++++++++++++++++----------
 1 files changed, 65 insertions(+), 24 deletions(-)
---
diff --git a/app/tools/gimpblendtool-editor.c b/app/tools/gimpblendtool-editor.c
index 0c323c4..4f45dbf 100644
--- a/app/tools/gimpblendtool-editor.c
+++ b/app/tools/gimpblendtool-editor.c
@@ -244,23 +244,42 @@ gimp_blend_tool_editor_line_prepare_to_remove_slider (GimpToolLine  *line,
 {
   if (remove)
     {
-      GimpGradient        *tentative_gradient;
-      GimpGradientSegment *seg;
-      gint                 i;
+      BlendInfo    *info;
+      GimpGradient *tentative_gradient;
 
-      tentative_gradient =
-        GIMP_GRADIENT (gimp_data_duplicate (GIMP_DATA (blend_tool->gradient)));
+      /* show a tentative gradient, demonstrating the result of actually
+       * removing the slider
+       */
 
-      seg = gimp_blend_tool_editor_handle_get_segment (blend_tool, slider);
+      info = blend_tool->undo_stack->data;
 
-      i = gimp_gradient_segment_range_get_n_segments (blend_tool->gradient,
-                                                      blend_tool->gradient->segments,
-                                                      seg) - 1;
+      if (info->added_handle == slider)
+        {
+          /* see comment in gimp_blend_tool_editor_delete_stop() */
 
-      seg = gimp_gradient_segment_get_nth (tentative_gradient->segments, i);
+          g_assert (info->gradient != NULL);
 
-      gimp_gradient_segment_range_merge (tentative_gradient,
-                                         seg, seg->next, NULL, NULL);
+          tentative_gradient = g_object_ref (info->gradient);
+        }
+      else
+        {
+          GimpGradientSegment *seg;
+          gint                 i;
+
+          tentative_gradient =
+            GIMP_GRADIENT (gimp_data_duplicate (GIMP_DATA (blend_tool->gradient)));
+
+          seg = gimp_blend_tool_editor_handle_get_segment (blend_tool, slider);
+
+          i = gimp_gradient_segment_range_get_n_segments (blend_tool->gradient,
+                                                          blend_tool->gradient->segments,
+                                                          seg) - 1;
+
+          seg = gimp_gradient_segment_get_nth (tentative_gradient->segments, i);
+
+          gimp_gradient_segment_range_merge (tentative_gradient,
+                                             seg, seg->next, NULL, NULL);
+        }
 
       gimp_blend_tool_set_tentative_gradient (blend_tool, tentative_gradient);
 
@@ -942,25 +961,47 @@ static void
 gimp_blend_tool_editor_delete_stop (GimpBlendTool *blend_tool,
                                     gint           slider)
 {
-  GimpGradientSegment *seg;
-  BlendInfo           *info;
+  BlendInfo *info;
 
   g_assert (gimp_blend_tool_editor_handle_is_stop (blend_tool, slider));
 
   gimp_blend_tool_editor_start_edit (blend_tool);
   gimp_blend_tool_editor_freeze_gradient (blend_tool);
 
-  seg = gimp_blend_tool_editor_handle_get_segment (blend_tool, slider);
-
-  gimp_gradient_segment_range_merge (blend_tool->gradient,
-                                     seg, seg->next, NULL, NULL);
-
   info = blend_tool->undo_stack->data;
 
   if (info->added_handle == slider)
-    info->added_handle = GIMP_TOOL_LINE_HANDLE_NONE;
+    {
+      /* when removing a stop that was added as part of the current action,
+       * restore the original gradient at the beginning of the action, rather
+       * than deleting the stop from the current gradient, so that the affected
+       * midpoint returns to its state at the beginning of the action, instead
+       * of being reset.
+       *
+       * note that this assumes that the gradient hasn't changed in any other
+       * way during the action, which is ugly, but currently always true.
+       */
+
+      g_assert (info->gradient != NULL);
+
+      gimp_data_copy (GIMP_DATA (blend_tool->gradient),
+                      GIMP_DATA (info->gradient));
+
+      g_clear_object (&info->gradient);
+
+      info->added_handle = GIMP_TOOL_LINE_HANDLE_NONE;
+    }
   else
-    info->removed_handle = slider;
+    {
+      GimpGradientSegment *seg;
+
+      seg = gimp_blend_tool_editor_handle_get_segment (blend_tool, slider);
+
+      gimp_gradient_segment_range_merge (blend_tool->gradient,
+                                         seg, seg->next, NULL, NULL);
+
+      info->removed_handle = slider;
+    }
 
   gimp_blend_tool_editor_thaw_gradient (blend_tool);
   gimp_blend_tool_editor_end_edit (blend_tool, FALSE);
@@ -1972,9 +2013,9 @@ gimp_blend_tool_editor_blend_info_apply (GimpBlendTool   *blend_tool,
         }
       else
         {
-          /* we're undoing an operation in which the same handle was added and
-           * then removed; don't change the selection
-           */
+          /* something went wrong... */
+          g_warn_if_reached ();
+
           set_selection = FALSE;
         }
     }