[gtk/wip/baedert/for-master: 40/46] gl renderer: Use premultiply() in inset shadow shader`

[Timm Bäder <baedert src gnome org>]

commit 1dcce8c3b7ebd6ef6d8279e3e9fe7de841ad8aba
Author: Timm Bäder <mail baedert org>
Date:   Wed Sep 30 06:00:50 2020 +0200

    gl renderer: Use premultiply() in inset shadow shader`

 gsk/resources/glsl/inset_shadow.glsl | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)
---
diff --git a/gsk/resources/glsl/inset_shadow.glsl b/gsk/resources/glsl/inset_shadow.glsl
index 6047946784..9a21cdef09 100644
--- a/gsk/resources/glsl/inset_shadow.glsl
+++ b/gsk/resources/glsl/inset_shadow.glsl
@@ -11,9 +11,7 @@ _OUT_ _GSK_ROUNDED_RECT_UNIFORM_ transformed_inside_outline;
 void main() {
   gl_Position = u_projection * u_modelview * vec4(aPosition, 0.0, 1.0);
 
-  final_color = u_color;
-  final_color.rgb *= final_color.a;
-  final_color *= u_alpha;
+  final_color = gsk_premultiply(u_color) * u_alpha;
 
   GskRoundedRect outside = gsk_create_rect(u_outline_rect);
   GskRoundedRect inside = gsk_rounded_rect_shrink(outside, vec4(u_spread));