Godot Loading Circle Shader

loading_circle.gd

shader_type canvas_item;

uniform vec3 rings[5]; // X=innerRadius, Y=outerRadius, Z=speed
uniform float timeScale = 1.0f;
uniform float blur = 1.0f;

void fragment() {
  vec2 p = 2.0*UV.xy - vec2(1.0);
  float radius = length(p);
  float angle = (atan(p.y, p.x)+PI) / (2.0*PI);
  float t = TIME*timeScale;

  float alpha = 0.0f;
  for (int i = 0; i < rings.length(); i++) {
    vec3 ring = rings[i];
    if (ring.z == 0.0) continue;

    bool flip = int(abs(ring.z*t))%2 - 1 == 0;
    float f = mod(ring.z*t,1.0);
    float lower = flip ? f: 0.0f;
    float upper = flip ? 1.0f: f;

    float dist = abs((ring.x+ring.y)/2.0 - radius) - (ring.y-ring.x)/2.0;
    if (dist < blur && lower < angle && angle < upper) {
      alpha = max(alpha, 1.0 - dist/blur * 100.0);
    }
  }
  COLOR.rgb = vec3(1.0f);
  COLOR.a = alpha;
}