【GLSL】RGBの円

See the Pen RGB circles by aadebdeb (@aadebdeb) on CodePen.

precision mediump float;

uniform float u_time;
uniform vec2 u_mouse;
uniform vec2 u_resolution;

float circle(in vec2 _position, in vec2 _center, in float _radius) {
    float d = distance(_position, _center);
    return 1. - smoothstep(_radius * 0.8, _radius * 1.8, d);
}

void main(void) {

  vec2 center = u_resolution / 2.;

  float radius = 200.;
  float angle = u_time * 0.001;
  float r = circle(gl_FragCoord.xy, center + radius * vec2(cos(angle), sin(angle)), 50.);
  float g = circle(gl_FragCoord.xy, center + radius * vec2(cos(angle * 2.), sin(angle * 2.)), 50.);
  float b = circle(gl_FragCoord.xy, center + radius * vec2(cos(angle * 4.), sin(angle * 4.)), 50.);

  gl_FragColor = vec4(r, g, b, 1.);
  // gl_FragColor = vec4(r - 1., g - 1., b - 1., 1.);
}