From b63ce7f900ee6a4631eacd1db07b2c9c9be12780 Mon Sep 17 00:00:00 2001
From: David Thompson <dthompson2@worcester.edu>
Date: Tue, 7 Sep 2021 20:12:35 -0400
Subject: graphics: path: Add support for linear/radial gradient fills.

---
 data/shaders/path-fill-frag.glsl | 28 +++++++++++++++++++++++++++-
 data/shaders/path-fill-vert.glsl |  9 ++++++++-
 2 files changed, 35 insertions(+), 2 deletions(-)

(limited to 'data')

diff --git a/data/shaders/path-fill-frag.glsl b/data/shaders/path-fill-frag.glsl
index 3af191f..e336e76 100644
--- a/data/shaders/path-fill-frag.glsl
+++ b/data/shaders/path-fill-frag.glsl
@@ -6,12 +6,38 @@ out vec4 fragColor;
 #define fragColor gl_FragColor
 #endif
 
+#ifdef GLSL120
+attribute vec2 fragPosition;
+#else
+in vec2 fragPosition;
+#endif
+
+uniform int mode;
 uniform vec4 color;
+uniform vec4 endColor;
+uniform mat3 gradientMatrix;
+uniform vec2 gradientRange;
+uniform float radialGradientRatio;
+
+vec4 gradientMix(float x) {
+  float start = gradientRange.x;
+  float end = gradientRange.y;
+  float t = clamp((x - start) / (end - start), 0.0, 1.0);
+  return mix(color, endColor, t);
+}
 
 void main(void) {
   if (color.a <= 0.0) {
     discard;
   }
 
-  fragColor = color;
+  if(mode == 0) { // solid color
+    fragColor = color;
+  } else if(mode == 1) { // linear gradient
+    float x = (gradientMatrix * vec3(fragPosition, 1.0)).x;
+    fragColor = gradientMix(x);
+  } else if(mode == 2) { // radial gradient
+    vec2 p = (gradientMatrix * vec3(fragPosition, 1.0)).xy;
+    fragColor = gradientMix(length(p * vec2(1.0, radialGradientRatio)));
+  }
 }
diff --git a/data/shaders/path-fill-vert.glsl b/data/shaders/path-fill-vert.glsl
index d95b71b..1752978 100644
--- a/data/shaders/path-fill-vert.glsl
+++ b/data/shaders/path-fill-vert.glsl
@@ -8,6 +8,12 @@ in vec2 position;
 attribute vec2 position;
 #endif
 
+#ifdef GLSL120
+varying vec2 fragPosition;
+#else
+out vec2 fragPosition;
+#endif
+
 uniform mat4 mvp;
 uniform vec4 color;
 
@@ -17,6 +23,7 @@ void main(void) {
   if (color.a <= 0.0) {
     gl_Position = vec4(0.0, 0.0, 0.0, 1.0);
   } else {
-    gl_Position = mvp * vec4(position.xy, 0.0, 1.0);
+    fragPosition = position;
+    gl_Position = mvp * vec4(position, 0.0, 1.0);
   }
 }
-- 
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