Reduced memory transfer of OpenGL gradient uniform upload. Rearranged gradient uniforms on OpenGL side to be more performant.

1 files changed, 22 insertions, 21 deletions

diff --git a/glow/src/shader/common/gradient.frag b/glow/src/shader/common/gradient.frag
index 1afb557d..89d2d398 100644
--- a/glow/src/shader/common/gradient.frag
+++ b/glow/src/shader/common/gradient.frag
@@ -1,6 +1,3 @@
-// GLSL does not support dynamically sized arrays without SSBOs
-#define MAX_STOPS 64
-
 #ifdef GL_ES
 #ifdef GL_FRAGMENT_PRECISION_HIGH
 precision highp float;
@@ -16,34 +13,38 @@ layout (location = 0) out vec4 fragColor;
 
 in vec2 raw_position;
 
-uniform vec2 gradient_start;
-uniform vec2 gradient_end;
-
+uniform vec4 gradient_direction;
 uniform uint color_stops_size;
-uniform float color_stop_offsets[MAX_STOPS];
-uniform vec4 color_stop_colors[MAX_STOPS];
+// GLSL does not support dynamically sized arrays without SSBOs so this is capped to 16 stops
+//stored as color(vec4) -> offset(vec4) sequentially;
+uniform vec4 color_stops[32];
 
 //TODO: rewrite without branching to make ALUs happy
 void main() {
-    vec2 gradient_vec = vec2(gradient_end - gradient_start);
-    vec2 current_vec = vec2(raw_position.xy - gradient_start);
+    vec2 start = gradient_direction.xy;
+    vec2 end = gradient_direction.zw;
+    vec2 gradient_vec = vec2(end - start);
+    vec2 current_vec = vec2(raw_position.xy - start);
     vec2 unit = normalize(gradient_vec);
     float coord_offset = dot(unit, current_vec) / length(gradient_vec);
 
-    for (uint i = 0; i < color_stops_size - 1; i++) {
-        float stop_offset = color_stop_offsets[i];
-        float next_stop_offset = color_stop_offsets[i + 1];
+    for (uint i = 0; i < color_stops_size - 2; i += 2) {
+        vec4 color = color_stops[i];
+        float offset = color_stops[i+1].x;
+
+        vec4 next_color = color_stops[i+2];
+        float next_offset = color_stops[i+3].x;
 
-        if (stop_offset <= coord_offset && coord_offset <= next_stop_offset) {
-            fragColor = mix(color_stop_colors[i], color_stop_colors[i+1], smoothstep(
-                stop_offset,
-                next_stop_offset,
+        if (offset <= coord_offset && coord_offset <= next_offset) {
+            fragColor = mix(color, next_color, smoothstep(
+                offset,
+                next_offset,
                 coord_offset
             ));
-        } else if (coord_offset < color_stop_offsets[0]) {
-            fragColor = color_stop_colors[0];
-        } else if (coord_offset > color_stop_offsets[color_stops_size - 1]) {
-            fragColor = color_stop_colors[color_stops_size - 1];
+        } else if (coord_offset < color_stops[1].x) {
+            fragColor = color_stops[0];
+        } else if (coord_offset > color_stops[color_stops_size - 1].x) {
+            fragColor = color_stops[color_stops_size - 2];
         }
     }
 }
\ No newline at end of file