[gnome-shell] scroll-view-fade: Clean up GLSL

[Jasper St. Pierre <jstpierre src gnome org>]

commit ae1a3a0cb24eb828e47e89f5560bb9cb03fcc0e5
Author: Jasper St. Pierre <jstpierre mecheye net>
Date:   Wed Nov 28 16:51:37 2012 -0500

    scroll-view-fade: Clean up GLSL
    
    Basic cleanup of what we're doing already. This moves a bunch
    of the "inside the fade area" checks to the top, before doing
    any calculations.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=689249

 src/st/st-scroll-view-fade.glsl |   18 ++++++++++++------
 1 files changed, 12 insertions(+), 6 deletions(-)
---
diff --git a/src/st/st-scroll-view-fade.glsl b/src/st/st-scroll-view-fade.glsl
index 2e40420..9248fa6 100644
--- a/src/st/st-scroll-view-fade.glsl
+++ b/src/st/st-scroll-view-fade.glsl
@@ -38,9 +38,15 @@ uniform mat2 fade_area;
 
 void main ()
 {
-    vec4 color = cogl_color_in * texture2D (tex, vec2 (cogl_tex_coord_in[0].xy));
+    cogl_color_out = cogl_color_in * texture2D (tex, vec2 (cogl_tex_coord_in[0].xy));
+
     float y = height * cogl_tex_coord_in[0].y;
     float x = width * cogl_tex_coord_in[0].x;
+
+    if (x < fade_area[0][0] || x > fade_area[1][0] ||
+        y < fade_area[0][1] || y > fade_area[1][1])
+        return;
+
     float ratio = 1.0;
     float fade_bottom_start = fade_area[1][1] - offset_bottom;
     float fade_right_start = fade_area[1][0] - offset_right;
@@ -49,10 +55,10 @@ void main ()
     float ratio_left = x / offset_left;
     float ratio_right = (fade_area[1][0] - x)/(fade_area[1][0] - fade_right_start);
     bool in_scroll_area = fade_area[0][0] <= x && fade_area[1][0] >= x;
-    bool fade_top = y < offset_top && in_scroll_area && (y >= fade_area[0][1]);
-    bool fade_bottom = y > fade_bottom_start && in_scroll_area && (y <= fade_area[1][1]);
-    bool fade_left = x < offset_left && in_scroll_area && (x >= fade_area[0][0]);
-    bool fade_right = x > fade_right_start && in_scroll_area && (x <= fade_area[1][0]);
+    bool fade_top = y < offset_top;
+    bool fade_bottom = y > fade_bottom_start;
+    bool fade_left = x < offset_left;
+    bool fade_right = x > fade_right_start;
 
     if (fade_top) {
         ratio *= ratio_top;
@@ -70,5 +76,5 @@ void main ()
         ratio *= ratio_right;
     }
 
-    cogl_color_out = color * ratio;
+    cogl_color_out *= ratio;
 }