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

diff --git a/src/st/st-scroll-view-fade.c b/src/st/st-scroll-view-fade.c
index 3c0c26bcea4c5eb3cd06ab0be763037fb5a0d3f2..9f267c3b662c7ef4d6a1e049132f3332a3c296f6 100644 (file)
--- 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 629c0143d5c635fbf25e2440158b7f225ca508b8..23881fb978fe13b600632d41700b05941c791e44 100644 (file)
--- 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) {