[gegl] color-overlay: fix output for semi-transparent color parameters

[Ell <ell src gnome org>]

commit dc32b3525530944ab5e47cc45f5be3c81623ed58
Author: Ell <ell_se yahoo com>
Date:   Wed Aug 22 14:03:48 2018 -0400

    color-overlay: fix output for semi-transparent color parameters
    
    Premultiply the color-parameter components by the alpha before
    processing.  Got lost during space invasion.

 operations/common/color-overlay.c | 4 ++++
 1 file changed, 4 insertions(+)
---
diff --git a/operations/common/color-overlay.c b/operations/common/color-overlay.c
index a18fac788..cd9489a1c 100644
--- a/operations/common/color-overlay.c
+++ b/operations/common/color-overlay.c
@@ -68,9 +68,13 @@ process (GeglOperation       *operation,
   const Babl     *format = gegl_operation_get_format (operation, "output");
   gfloat          color[4];
   gfloat          alpha_c;
+  gint            i;
 
   gegl_color_get_pixel (o->value, format, &color);
 
+  for (i = 0; i < 3; i++)
+    color[i] *= color[3];
+
   alpha_c = 1.0f - color[3];
 
   if (fabs (alpha_c) <= EPSILON)