hex shader: rainbow shimmer on edges when wave passes

modules/hex_wave.frag

@@ -22,6 +22,11 @@ float sdHexagon(vec2 p, float r) {
     return length(p) * sign(p.y);
 }
 
+// Rainbow from angle — color picker style
+vec3 hsv2rgb(float h) {
+    return clamp(abs(mod(h * 6.0 + vec3(0.0, 4.0, 2.0), 6.0) - 3.0) - 1.0, 0.0, 1.0);
+}
+
 void main() {
     vec2 res = uResolution.xy;
     vec2 frag = qt_TexCoord0 * res;
@@ -43,6 +48,7 @@ void main() {
 
     vec2 p = frag - center;
     float d = sdHexagon(p.yx, inradius);  // swap for flat-top
+
     if (d > 0.0) {
         fragColor = vec4(0.0);
         return;
@@ -63,7 +69,23 @@ void main() {
     rgb = min(rgb + vec3(0.3 * wf), vec3(1.0));
     a += 0.12 * wf;
 
-    // Anti-alias
+    // Rainbow shimmer on hex edges when wave passes
+    float edgeWidth = 2.0;
+    float edgeFactor = smoothstep(-edgeWidth, 0.0, d);  // 0 at interior, 1 at edge
+    if (wf > 0.01 && edgeFactor > 0.0) {
+        // Angle around hex center → hue
+        float angle = atan(p.y, p.x);
+        float hue = (angle + 3.14159) / 6.28318;
+        // Shift hue by position so neighboring hexes have different phase
+        hue = fract(hue + center.x * 0.003 + center.y * 0.005);
+        vec3 rainbow = hsv2rgb(hue);
+
+        float shimmer = edgeFactor * wf;
+        rgb = mix(rgb, rainbow, shimmer * 0.8);
+        a = mix(a, 0.5, shimmer * 0.6);
+    }
+
+    // Anti-alias outer edge
     float aa = 1.0 - smoothstep(-1.0, 0.0, d);
     a *= aa;