[gimp] Issue #1975 - Color to alpha now requires an alpha-channel ...

[Ell <ell src gnome org>]

commit 50b655de270208956d570cb56e3f6d219ccb7e85
Author: Ell <ell_se yahoo com>
Date:   Fri Jan 17 10:51:30 2020 +0200

    Issue #1975 - Color to alpha now requires an alpha-channel ...
    
    ... (used to add one automatically)
    
    In GimpFilterTool and gimp_drawable_apply_operation(), use
    gimp_drawable_filter_set_add_alpha() to add an alpha channel when
    applying an operation that specifies "needs-alpha" to a drawable
    that can have alpha.
    
    Don't disable gegl:color-to-alpha (which has "needs-alpha") when
    the drawable doesn't have an alpha channel, if one can be added.

 app/actions/filters-actions.c     | 16 +++++++++-------
 app/core/gimpdrawable-operation.c |  8 ++++++++
 app/pdb/plug-in-compat-cmds.c     |  2 +-
 app/tools/gimpfiltertool.c        | 37 ++++++++++++++++++++++++-------------
 pdb/groups/plug_in_compat.pdb     |  2 +-
 5 files changed, 43 insertions(+), 22 deletions(-)
---
diff --git a/app/actions/filters-actions.c b/app/actions/filters-actions.c
index 29a7949f54..f5fb1cb856 100644
--- a/app/actions/filters-actions.c
+++ b/app/actions/filters-actions.c
@@ -842,10 +842,11 @@ filters_actions_update (GimpActionGroup *group,
                         gpointer         data)
 {
   GimpImage    *image;
-  GimpDrawable *drawable = NULL;
-  gboolean      writable = FALSE;
-  gboolean      gray     = FALSE;
-  gboolean      alpha    = FALSE;
+  GimpDrawable *drawable       = NULL;
+  gboolean      writable       = FALSE;
+  gboolean      gray           = FALSE;
+  gboolean      alpha          = FALSE;
+  gboolean      supports_alpha = FALSE;
 
   image = action_data_get_image (data);
 
@@ -857,8 +858,9 @@ filters_actions_update (GimpActionGroup *group,
         {
           GimpItem *item;
 
-          alpha = gimp_drawable_has_alpha (drawable);
-          gray  = gimp_drawable_is_gray (drawable);
+          gray           = gimp_drawable_is_gray (drawable);
+          alpha          = gimp_drawable_has_alpha (drawable);
+          supports_alpha = gimp_drawable_supports_alpha (drawable);
 
           if (GIMP_IS_LAYER_MASK (drawable))
             item = GIMP_ITEM (gimp_layer_mask_get_layer (GIMP_LAYER_MASK (drawable)));
@@ -893,7 +895,7 @@ filters_actions_update (GimpActionGroup *group,
   SET_SENSITIVE ("filters-dither",                  writable);
   SET_SENSITIVE ("filters-color-rotate",            writable);
   SET_SENSITIVE ("filters-color-temperature",       writable && !gray);
-  SET_SENSITIVE ("filters-color-to-alpha",          writable && !gray && alpha);
+  SET_SENSITIVE ("filters-color-to-alpha",          writable && !gray && supports_alpha);
   SET_SENSITIVE ("filters-component-extract",       writable);
   SET_SENSITIVE ("filters-convolution-matrix",      writable);
   SET_SENSITIVE ("filters-cubism",                  writable);
diff --git a/app/core/gimpdrawable-operation.c b/app/core/gimpdrawable-operation.c
index d4994fa3b4..3e64ab4d89 100644
--- a/app/core/gimpdrawable-operation.c
+++ b/app/core/gimpdrawable-operation.c
@@ -27,6 +27,8 @@
 
 #include "core-types.h"
 
+#include "gegl/gimp-gegl-utils.h"
+
 #include "gimpdrawable.h"
 #include "gimpdrawable-operation.h"
 #include "gimpdrawablefilter.h"
@@ -58,6 +60,12 @@ gimp_drawable_apply_operation (GimpDrawable *drawable,
 
   filter = gimp_drawable_filter_new (drawable, undo_desc, operation, NULL);
 
+  if (gimp_drawable_supports_alpha (drawable) &&
+      gimp_gegl_node_get_key (operation, "needs-alpha"))
+    {
+      gimp_drawable_filter_set_add_alpha (filter, TRUE);
+    }
+
   gimp_drawable_filter_apply  (filter, NULL);
   gimp_drawable_filter_commit (filter, progress, TRUE);
 
diff --git a/app/pdb/plug-in-compat-cmds.c b/app/pdb/plug-in-compat-cmds.c
index ebcb2326e4..539d43fbb4 100644
--- a/app/pdb/plug-in-compat-cmds.c
+++ b/app/pdb/plug-in-compat-cmds.c
@@ -1083,7 +1083,7 @@ plug_in_colortoalpha_invoker (GimpProcedure         *procedure,
                                      GIMP_PDB_ITEM_CONTENT, error) &&
           gimp_pdb_item_is_not_group (GIMP_ITEM (drawable), error))
         {
-          /* XXX: fixme disable for gray, and add alpha when needed */
+          /* XXX: fixme disable for gray */
 
           GeglColor *gegl_color = gimp_gegl_color_new (&color, NULL);
           GeglNode  *node =
diff --git a/app/tools/gimpfiltertool.c b/app/tools/gimpfiltertool.c
index 54334c03bc..326603b2f3 100644
--- a/app/tools/gimpfiltertool.c
+++ b/app/tools/gimpfiltertool.c
@@ -1384,23 +1384,34 @@ gimp_filter_tool_update_filter (GimpFilterTool *filter_tool)
 {
   GimpTool          *tool    = GIMP_TOOL (filter_tool);
   GimpFilterOptions *options = GIMP_FILTER_TOOL_GET_OPTIONS (filter_tool);
+  const gchar       *operation_name;
+  gboolean           add_alpha;
+  gboolean           clip;
 
   if (! filter_tool->filter)
     return;
 
-  gimp_drawable_filter_set_clip          (filter_tool->filter,
-                                          options->clip ==
-                                          GIMP_TRANSFORM_RESIZE_CLIP ||
-                                          ! gimp_drawable_has_alpha (
-                                              tool->drawable));
-  gimp_drawable_filter_set_region        (filter_tool->filter,
-                                          options->region);
-  gimp_drawable_filter_set_preview       (filter_tool->filter,
-                                          options->preview_split,
-                                          options->preview_alignment,
-                                          options->preview_position);
-  gimp_drawable_filter_set_gamma_hack    (filter_tool->filter,
-                                          options->gamma_hack);
+  operation_name = gegl_node_get_operation (filter_tool->operation);
+
+  add_alpha = gimp_drawable_supports_alpha (tool->drawable) &&
+              operation_name                                &&
+              gegl_operation_get_key (operation_name, "needs-alpha");
+  clip      = options->clip == GIMP_TRANSFORM_RESIZE_CLIP ||
+              ! (gimp_drawable_has_alpha (tool->drawable) ||
+                 add_alpha);
+
+  gimp_drawable_filter_set_clip       (filter_tool->filter,
+                                       clip);
+  gimp_drawable_filter_set_region     (filter_tool->filter,
+                                       options->region);
+  gimp_drawable_filter_set_preview    (filter_tool->filter,
+                                       options->preview_split,
+                                       options->preview_alignment,
+                                       options->preview_position);
+  gimp_drawable_filter_set_add_alpha  (filter_tool->filter,
+                                       add_alpha);
+  gimp_drawable_filter_set_gamma_hack (filter_tool->filter,
+                                       options->gamma_hack);
 }
 
 static void
diff --git a/pdb/groups/plug_in_compat.pdb b/pdb/groups/plug_in_compat.pdb
index c9136b7395..a97216d71f 100644
--- a/pdb/groups/plug_in_compat.pdb
+++ b/pdb/groups/plug_in_compat.pdb
@@ -788,7 +788,7 @@ HELP
                                  GIMP_PDB_ITEM_CONTENT, error) &&
       gimp_pdb_item_is_not_group (GIMP_ITEM (drawable), error))
     {
-      /* XXX: fixme disable for gray, and add alpha when needed */
+      /* XXX: fixme disable for gray */
 
       GeglColor *gegl_color = gimp_gegl_color_new (&color, NULL);
       GeglNode  *node =