[gtk] gl renderer: Fix color matrix shader

[Timm Bäder <baedert src gnome org>]

commit a2518493a2bbd77d205d65c3886fe426c5030a9d
Author: Timm Bäder <mail baedert org>
Date:   Sat May 18 09:33:38 2019 +0200

    gl renderer: Fix color matrix shader
    
    We *just* computed a un-premultiplied color, maybe we should also use
    it.

 gsk/resources/glsl/color_matrix.fs.glsl | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/gsk/resources/glsl/color_matrix.fs.glsl b/gsk/resources/glsl/color_matrix.fs.glsl
index 07875fe0b4..284e0a9e65 100644
--- a/gsk/resources/glsl/color_matrix.fs.glsl
+++ b/gsk/resources/glsl/color_matrix.fs.glsl
@@ -11,7 +11,7 @@ void main() {
   if (color.a != 0.0)
     color.rgb /= color.a;
 
-  color = u_color_matrix * diffuse + u_color_offset;
+  color = u_color_matrix * color + u_color_offset;
   color = clamp(color, 0.0f, 1.0f);
 
   color.rgb *= color.a;