[gnome-shell] st-scroll-view-fade: Reduce number of GLSL uniforms and instructions

[Adel Gadllah <agadllah src gnome org>]

commit 4095a58eb9a2921c178b30c56d1fbe7662c2778a
Author: Adel Gadllah <adel gadllah gmail com>
Date:   Fri Sep 13 09:33:27 2013 +0200

    st-scroll-view-fade: Reduce number of GLSL uniforms and instructions
    
    The vvalue and hvalue uniforms are only used to decide whether we
    should do fade the edges or not based on the fade_edges uniform.
    The result does not change accross fragments so there is no reason
    to recompute it for every fragment (pixel) so just split the edge
    fade into two uniforms and compute the "should we fade the edges"
    boolean once for every direction (when setting the uniforms) instead
    of for every single fragment twice.
    
    This reduces the number of uniforms as well as the the number of instructions
    which are limited on older hardware. It should also be more efficent.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=708007

 src/st/st-scroll-view-fade.c    |    5 ++---
 src/st/st-scroll-view-fade.glsl |   17 ++++++-----------
 2 files changed, 8 insertions(+), 14 deletions(-)
---
diff --git a/src/st/st-scroll-view-fade.c b/src/st/st-scroll-view-fade.c
index 3c0c26b..9f267c3 100644
--- a/src/st/st-scroll-view-fade.c
+++ b/src/st/st-scroll-view-fade.c
@@ -142,18 +142,17 @@ st_scroll_view_fade_paint_target (ClutterOffscreenEffect *effect)
 
   st_adjustment_get_values (self->vadjustment, &value, &lower, &upper, NULL, NULL, &page_size);
   value = (value - lower) / (upper - page_size - lower);
-  clutter_shader_effect_set_uniform (shader, "vvalue", G_TYPE_FLOAT, 1, value);
+  clutter_shader_effect_set_uniform (shader, "fade_edges_v", G_TYPE_INT, 1, self->fade_edges ? value >= 0.0 
: value > 0.0);
 
   st_adjustment_get_values (self->hadjustment, &value, &lower, &upper, NULL, NULL, &page_size);
   value = (value - lower) / (upper - page_size - lower);
-  clutter_shader_effect_set_uniform (shader, "hvalue", G_TYPE_FLOAT, 1, value);
+  clutter_shader_effect_set_uniform (shader, "fade_edges_h", G_TYPE_INT, 1, self->fade_edges ? value >= 0.0 
: value > 0.0);
 
   clutter_shader_effect_set_uniform (shader, "vfade_offset", G_TYPE_FLOAT, 1, self->vfade_offset);
   clutter_shader_effect_set_uniform (shader, "hfade_offset", G_TYPE_FLOAT, 1, self->hfade_offset);
   clutter_shader_effect_set_uniform (shader, "tex", G_TYPE_INT, 1, 0);
   clutter_shader_effect_set_uniform (shader, "height", G_TYPE_FLOAT, 1, clutter_actor_get_height 
(self->actor));
   clutter_shader_effect_set_uniform (shader, "width", G_TYPE_FLOAT, 1, clutter_actor_get_width 
(self->actor));
-  clutter_shader_effect_set_uniform (shader, "fade_edges", G_TYPE_INT, 1, self->fade_edges);
   clutter_shader_effect_set_uniform (shader, "fade_area_topleft", CLUTTER_TYPE_SHADER_FLOAT, 2, 
fade_area_topleft);
   clutter_shader_effect_set_uniform (shader, "fade_area_bottomright", CLUTTER_TYPE_SHADER_FLOAT, 2, 
fade_area_bottomright);
 
diff --git a/src/st/st-scroll-view-fade.glsl b/src/st/st-scroll-view-fade.glsl
index 629c014..23881fb 100644
--- a/src/st/st-scroll-view-fade.glsl
+++ b/src/st/st-scroll-view-fade.glsl
@@ -22,9 +22,8 @@ uniform float height;
 uniform float width;
 uniform float vfade_offset;
 uniform float hfade_offset;
-uniform float vvalue;
-uniform float hvalue;
-uniform bool  fade_edges;
+uniform bool  fade_edges_h;
+uniform bool  fade_edges_v;
 
 uniform vec2 fade_area_topleft;
 uniform vec2 fade_area_bottomright;
@@ -45,14 +44,10 @@ void main ()
         float ratio = 1.0;
         float fade_bottom_start = fade_area_bottomright[1] - vfade_offset;
         float fade_right_start = fade_area_bottomright[0] - hfade_offset;
-        bool fade_top = y < vfade_offset && (fade_edges ? vvalue >= 0.0
-                                                        : vvalue > 0.0);
-        bool fade_bottom = y > fade_bottom_start && (fade_edges ? vvalue <= 1.0
-                                                                : vvalue < 1.0);
-        bool fade_left = x < hfade_offset && (fade_edges ? hvalue >= 0.0
-                                                         : hvalue > 0.0);
-        bool fade_right = x > fade_right_start && (fade_edges ? hvalue <= 1.0
-                                                              : hvalue < 1.0);
+        bool fade_top = y < vfade_offset && fade_edges_v;
+        bool fade_bottom = y > fade_bottom_start && fade_edges_v;
+        bool fade_left = x < hfade_offset && fade_edges_h;
+        bool fade_right = x > fade_right_start && fade_edges_h;
 
         float vfade_scale = height / vfade_offset;
         if (fade_top) {