[gimp] app: make luminance blend mode depend on space

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

commit 19e74f0e286df21c6fb655a3f98dc444ba8ef6a6
Author: Elle Stone <ellestone ninedegreesbelow com>
Date:   Sun Jun 9 13:59:30 2019 -0400

    app: make luminance blend mode depend on space
    
    Fixes issue #3451 Space invasion/AnyRGB: Luminance blend mode doesn't work
    
    It might be faster to fetch the RGB luminance and do the computation
    ourselves than looking up the same fish for each processing request, at
    least now we're faster. (commit message and code slightly revised by pippin)

 app/operations/layer-modes/gimpoperationlayermode-blend.c | 15 ++++++++-------
 1 file changed, 8 insertions(+), 7 deletions(-)
---
diff --git a/app/operations/layer-modes/gimpoperationlayermode-blend.c 
b/app/operations/layer-modes/gimpoperationlayermode-blend.c
index e107462d09..8087f98bf9 100644
--- a/app/operations/layer-modes/gimpoperationlayermode-blend.c
+++ b/app/operations/layer-modes/gimpoperationlayermode-blend.c
@@ -891,13 +891,14 @@ gimp_operation_layer_mode_blend_luminance (GeglOperation *operation,
                                            gfloat        *comp,
                                            gint           samples)
 {
-  static const Babl *fish;
-  gfloat            *scratch;
-  gfloat            *in_Y;
-  gfloat            *layer_Y;
-
-  if (! fish)
-    fish = babl_fish ("RGBA float", "Y float");
+  const Babl *fish;
+  gfloat     *scratch;
+  gfloat     *in_Y;
+  gfloat     *layer_Y;
+  const Babl *space = gegl_operation_get_source_space (operation, "input");
+
+  fish  = babl_fish (babl_format_with_space ("RGBA float", space),
+                     babl_format_with_space ("Y float", space));
 
   scratch = gegl_scratch_new (gfloat, 2 * samples);