From 0c4a79dd8da6f002220533281abc3d45ebfd391d Mon Sep 17 00:00:00 2001
From: David Thompson <dthompson2@worcester.edu>
Date: Wed, 8 Sep 2021 07:38:07 -0400
Subject: graphics: path: Move gradient matrix multiplication to vertex shader.

*Much* cheaper to do this per-vertex than per-fragment.
---
 data/shaders/path-fill-frag.glsl | 8 +++-----
 data/shaders/path-fill-vert.glsl | 3 ++-
 2 files changed, 5 insertions(+), 6 deletions(-)

diff --git a/data/shaders/path-fill-frag.glsl b/data/shaders/path-fill-frag.glsl
index e336e76..ba9c5a6 100644
--- a/data/shaders/path-fill-frag.glsl
+++ b/data/shaders/path-fill-frag.glsl
@@ -15,7 +15,6 @@ in vec2 fragPosition;
 uniform int mode;
 uniform vec4 color;
 uniform vec4 endColor;
-uniform mat3 gradientMatrix;
 uniform vec2 gradientRange;
 uniform float radialGradientRatio;
 
@@ -34,10 +33,9 @@ void main(void) {
   if(mode == 0) { // solid color
     fragColor = color;
   } else if(mode == 1) { // linear gradient
-    float x = (gradientMatrix * vec3(fragPosition, 1.0)).x;
-    fragColor = gradientMix(x);
+    fragColor = gradientMix(fragPosition.x);
   } else if(mode == 2) { // radial gradient
-    vec2 p = (gradientMatrix * vec3(fragPosition, 1.0)).xy;
-    fragColor = gradientMix(length(p * vec2(1.0, radialGradientRatio)));
+    vec2 p = fragPosition * vec2(1.0, radialGradientRatio);
+    fragColor = gradientMix(length(p));
   }
 }
diff --git a/data/shaders/path-fill-vert.glsl b/data/shaders/path-fill-vert.glsl
index 1752978..d66bb14 100644
--- a/data/shaders/path-fill-vert.glsl
+++ b/data/shaders/path-fill-vert.glsl
@@ -16,6 +16,7 @@ out vec2 fragPosition;
 
 uniform mat4 mvp;
 uniform vec4 color;
+uniform mat3 gradientMatrix;
 
 void main(void) {
   // Short-circuit because the fragments will just be discarded
@@ -23,7 +24,7 @@ void main(void) {
   if (color.a <= 0.0) {
     gl_Position = vec4(0.0, 0.0, 0.0, 1.0);
   } else {
-    fragPosition = position;
+    fragPosition = (gradientMatrix * vec3(position, 1.0)).xy;
     gl_Position = mvp * vec4(position, 0.0, 1.0);
   }
 }
-- 
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