[gimp] app: gimp:set-alpha propagate space

[Øyvind "pippin" Kolås <ok src gnome org>]

commit f3a757ff33c90151d37af68668cbbe9920f30d24
Author: Øyvind Kolås <pippin gimp org>
Date:   Fri Jul 6 15:03:37 2018 +0200

    app: gimp:set-alpha propagate space

 app/operations/gimpoperationsetalpha.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)
---
diff --git a/app/operations/gimpoperationsetalpha.c b/app/operations/gimpoperationsetalpha.c
index 29ae0a7d31..a575b61273 100644
--- a/app/operations/gimpoperationsetalpha.c
+++ b/app/operations/gimpoperationsetalpha.c
@@ -136,9 +136,10 @@ gimp_operation_set_alpha_set_property (GObject      *object,
 static void
 gimp_operation_set_alpha_prepare (GeglOperation *operation)
 {
-  gegl_operation_set_format (operation, "input",  babl_format ("RGBA float"));
-  gegl_operation_set_format (operation, "aux",    babl_format ("Y float"));
-  gegl_operation_set_format (operation, "output", babl_format ("RGBA float"));
+  const Babl *space = gegl_operation_get_source_space (operation, "input");
+  gegl_operation_set_format (operation, "input",  babl_format_with_space ("RGBA float", space));
+  gegl_operation_set_format (operation, "aux",    babl_format_with_space ("Y float", space));
+  gegl_operation_set_format (operation, "output", babl_format_with_space ("RGBA float", space));
 }
 
 static gboolean