【GLSL】マウスに添って広がる円

See the Pen a circle by aadebdeb (@aadebdeb) on CodePen.

precision mediump float;

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

void main(void) {
  float d = distance(gl_FragCoord.xy, u_resolution.xy / 2.);
  float v = step(distance(u_mouse, u_resolution.xy / 2.), d);
  gl_FragColor = vec4(vec3(v), 1.);
}