Drop, smash,
shade, share.

uniform float u_time;
uniform float u_scanSpeed;
uniform float u_rainbowScale;
varying vec2 vUv;
varying vec3 vNormal;
varying vec3 vPosition;
varying vec3 vViewDir;

vec3 hsv2rgb(vec3 c) {
  vec4 K = vec4(1.0, 2.0/3.0, 1.0/3.0, 3.0);
  vec3 p = abs(fract(c.xxx + K.xyz) * 6.0 - K.www);
  return c.z * mix(K.xxx, clamp(p - K.xxx, 0.0, 1.0), c.y);
}

void main() {
  float fresnel = pow(1.0 - max(dot(vNormal, vViewDir), 0.0), 3.0);
  float hue = fract(vUv.y * u_rainbowScale + u_time * 0.2 + fresnel * 0.5);
  vec3 rainbow = hsv2rgb(vec3(hue, 0.8, 1.0));
  float scanline = sin(vUv.y * 80.0 + u_time * u_scanSpeed) * 0.5 + 0.5;
  scanline = smoothstep(0.3, 0.7, scanline) * 0.15;
  vec3 color = mix(rainbow * 0.6, vec3(1.0), fresnel * 0.7) + scanline;
  gl_FragColor = vec4(color, 1.0);
}