[gtk] gl renderer: use w axis vector from graphene

[Timm Bäder <baedert src gnome org>]

commit 4ab3aada3f7bc1cdf8aa1690931ea8bc34e1a500
Author: Timm Bäder <mail baedert org>
Date:   Sun May 27 18:05:00 2018 +0200

    gl renderer: use w axis vector from graphene
    
    Instead of initializing our own one every time.

 gsk/gl/gskglrenderer.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)
---
diff --git a/gsk/gl/gskglrenderer.c b/gsk/gl/gskglrenderer.c
index 3f14304b94..5d9c92cf48 100644
--- a/gsk/gl/gskglrenderer.c
+++ b/gsk/gl/gskglrenderer.c
@@ -201,15 +201,13 @@ color_matrix_modifies_alpha (GskRenderNode *node)
   const graphene_matrix_t *matrix = gsk_color_matrix_node_peek_color_matrix (node);
   const graphene_vec4_t *offset = gsk_color_matrix_node_peek_color_offset (node);
   graphene_vec4_t row3;
-  graphene_vec4_t id_row3;
 
   if (graphene_vec4_get_w (offset) != 0.0f)
     return TRUE;
 
-  graphene_vec4_init (&id_row3, 0, 0, 0, 1);
   graphene_matrix_get_row (matrix, 3, &row3);
 
-  return !graphene_vec4_equal (&id_row3, &row3);
+  return !graphene_vec4_equal (graphene_vec4_w_axis (), &row3);
 }
 
 static inline void