[gimp] app: pad flipped/rotated drawables with transparency, not bg color

[N/A <ell src gnome org>]

commit 20ccc4ed59d8b8ee5ba6b8272e61f90d3147eed5
Author: Ell <ell_se yahoo com>
Date:   Sun Jun 11 11:49:00 2017 -0400

    app: pad flipped/rotated drawables with transparency, not bg color
    
    ... when clipping, if they have an alpha channel
    
    Right now, this case is only reachable through PDB, but it will become
    relevant for the flip tool soon.

 app/core/gimpdrawable-transform.c |   24 +++++++++++++++++-------
 1 files changed, 17 insertions(+), 7 deletions(-)
---
diff --git a/app/core/gimpdrawable-transform.c b/app/core/gimpdrawable-transform.c
index 218e62e..5162adc 100644
--- a/app/core/gimpdrawable-transform.c
+++ b/app/core/gimpdrawable-transform.c
@@ -158,6 +158,7 @@ gimp_drawable_transform_buffer_flip (GimpDrawable        *drawable,
                                      gint                *new_offset_x,
                                      gint                *new_offset_y)
 {
+  const Babl    *format;
   GeglBuffer    *new_buffer;
   GeglRectangle  src_rect;
   GeglRectangle  dest_rect;
@@ -205,9 +206,11 @@ gimp_drawable_transform_buffer_flip (GimpDrawable        *drawable,
       break;
     }
 
+  format = gegl_buffer_get_format (orig_buffer);
+
   new_buffer = gegl_buffer_new (GEGL_RECTANGLE (0, 0,
                                                 new_width, new_height),
-                                gegl_buffer_get_format (orig_buffer));
+                                format);
 
   if (clip_result && (new_x != orig_x || new_y != orig_y))
     {
@@ -219,8 +222,10 @@ gimp_drawable_transform_buffer_flip (GimpDrawable        *drawable,
       *new_offset_x = orig_x;
       *new_offset_y = orig_y;
 
-      /*  "Outside" a channel is transparency, not the bg color  */
-      if (GIMP_IS_CHANNEL (drawable))
+      /*  Use transparency, rather than the bg color, as the "outside" color of
+       *  channels, and drawables with an alpha channel.
+       */
+      if (GIMP_IS_CHANNEL (drawable) || babl_format_has_alpha (format))
         {
           gimp_rgba_set (&bg, 0.0, 0.0, 0.0, 0.0);
         }
@@ -360,6 +365,7 @@ gimp_drawable_transform_buffer_rotate (GimpDrawable      *drawable,
                                        gint              *new_offset_x,
                                        gint              *new_offset_y)
 {
+  const Babl    *format;
   GeglBuffer    *new_buffer;
   GeglRectangle  src_rect;
   GeglRectangle  dest_rect;
@@ -420,6 +426,8 @@ gimp_drawable_transform_buffer_rotate (GimpDrawable      *drawable,
       break;
     }
 
+  format = gegl_buffer_get_format (orig_buffer);
+
   if (clip_result && (new_x != orig_x || new_y != orig_y ||
                       new_width != orig_width || new_height != orig_height))
 
@@ -431,13 +439,15 @@ gimp_drawable_transform_buffer_rotate (GimpDrawable      *drawable,
 
       new_buffer = gegl_buffer_new (GEGL_RECTANGLE (0, 0,
                                                     orig_width, orig_height),
-                                    gegl_buffer_get_format (orig_buffer));
+                                    format);
 
       *new_offset_x = orig_x;
       *new_offset_y = orig_y;
 
-      /*  "Outside" a channel is transparency, not the bg color  */
-      if (GIMP_IS_CHANNEL (drawable))
+      /*  Use transparency, rather than the bg color, as the "outside" color of
+       *  channels, and drawables with an alpha channel.
+       */
+      if (GIMP_IS_CHANNEL (drawable) || babl_format_has_alpha (format))
         {
           gimp_rgba_set (&bg, 0.0, 0.0, 0.0, 0.0);
         }
@@ -514,7 +524,7 @@ gimp_drawable_transform_buffer_rotate (GimpDrawable      *drawable,
     {
       new_buffer = gegl_buffer_new (GEGL_RECTANGLE (0, 0,
                                                     new_width, new_height),
-                                    gegl_buffer_get_format (orig_buffer));
+                                    format);
 
       *new_offset_x = new_x;
       *new_offset_y = new_y;