[gimp/gimp-2-10] Issue #1677 - Alpha channel copy / Layer Mask issues

[Michael Natterer <mitch src gnome org>]

commit 8146da9930b574feeb1fffe2345a9a739325ebaf
Author: Michael Natterer <mitch gimp org>
Date:   Tue Jun 19 12:37:59 2018 +0200

    Issue #1677 - Alpha channel copy / Layer Mask issues
    
    gimp_layer_create_mask(): make sure we don't do a gamma conversion
    when initializing the mask from a channel. This was probably not the
    last place to need this fix.
    
    Also get rid of a second switch(add_mask_type), must be some leftover
    from long gone logic.
    
    (cherry picked from commit f815a2d922c6a301d34714d623db4f10848f1d5b)

 app/core/gimplayer.c | 22 +++++++++-------------
 1 file changed, 9 insertions(+), 13 deletions(-)
---
diff --git a/app/core/gimplayer.c b/app/core/gimplayer.c
index 0b25e79f1f..c5913a6c37 100644
--- a/app/core/gimplayer.c
+++ b/app/core/gimplayer.c
@@ -1919,20 +1919,10 @@ gimp_layer_create_mask (GimpLayer       *layer,
     {
     case GIMP_ADD_MASK_WHITE:
       gimp_channel_all (GIMP_CHANNEL (mask), FALSE);
-      return mask;
-
-    case GIMP_ADD_MASK_BLACK:
-      gimp_channel_clear (GIMP_CHANNEL (mask), NULL, FALSE);
-      return mask;
-
-    default:
       break;
-    }
 
-  switch (add_mask_type)
-    {
-    case GIMP_ADD_MASK_WHITE:
     case GIMP_ADD_MASK_BLACK:
+      gimp_channel_clear (GIMP_CHANNEL (mask), NULL, FALSE);
       break;
 
     case GIMP_ADD_MASK_ALPHA:
@@ -2001,12 +1991,17 @@ gimp_layer_create_mask (GimpLayer       *layer,
 
         if ((copy_width || copy_height) && ! channel_empty)
           {
-            GeglBuffer    *src;
-            GeglBuffer    *dest;
+            GeglBuffer *src;
+            GeglBuffer *dest;
+            const Babl *format;
 
             src  = gimp_drawable_get_buffer (GIMP_DRAWABLE (channel));
             dest = gimp_drawable_get_buffer (GIMP_DRAWABLE (mask));
 
+            format = gegl_buffer_get_format (src);
+
+            /* make sure no gamma conversion happens */
+            gegl_buffer_set_format (dest, format);
             gimp_gegl_buffer_copy (src,
                                    GEGL_RECTANGLE (copy_x, copy_y,
                                                    copy_width, copy_height),
@@ -2015,6 +2010,7 @@ gimp_layer_create_mask (GimpLayer       *layer,
                                    GEGL_RECTANGLE (copy_x - offset_x,
                                                    copy_y - offset_y,
                                                    0, 0));
+            gegl_buffer_set_format (dest, NULL);
 
             GIMP_CHANNEL (mask)->bounds_known = FALSE;
           }