Spiral.frag shader using editor.thebookofshaders.com

Spiral.frag

// Author: 
// Title: 

#ifdef GL_ES
precision mediump float;
#endif

#define M_PI 3.14159265358979
#define M_2PI 6.28318530717958
#define RADIUS 100.0

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

void main() {
    vec2 center = u_resolution.xy * 0.5;
    vec2 normCenter = vec2(0.5);
    vec2 uv = gl_FragCoord.xy;
    vec2 normUV = gl_FragCoord.xy / u_resolution.xy;
    
    vec2 centerToUV = normUV - normCenter;
    float lengthCenterToUV = length(centerToUV);
    
    //atan gives value between -pi and pi.. so first adding pi.. which makes the value between 0 and 2pi
    //then scaling it back to 0 and 1 by dividing by 2pi
    float theta = (atan(centerToUV.y, centerToUV.x) - M_PI) / M_2PI * -1.;
    //if theta is 0 that means atan value is -pi
    //if theta is 1 that means atan value is pi
    //if theta is 0.5 that means atan value is 0

    float mult = 0.1;
    float col = 0.;
    for (int i=0; i<4; i++) {
        float index = float(i);
        float ringPre = (theta + index - 1.) * mult;
        if (i == 0) {
            ringPre = 0.;
        }
        float ringPost = (theta + index) * mult;
        float stepVal = step(ringPre, lengthCenterToUV) - step(ringPost, lengthCenterToUV);
        col += (stepVal * (theta + index) * 0.25);
    }

    vec3 color = vec3(col);

    float timeFactor = cos(u_time * 0.8) * 0.5 + 0.5;
    col += (timeFactor);
    if (col > 1.0)
        col = (col - 1.0);
    color = vec3(col);

    //color lerp
    float rate = col;
    
    vec3 color1 = vec3(1., 0., 1.);
    vec3 color2 = vec3(1., 1., 0.);
    vec3 color3 = vec3(0., 1., 0.6);
    vec3 color4 = vec3(0., 1., 1.);
    vec3 color5 = vec3(0.6, 0., 1.);
    vec3 color6 = vec3(1., 0., 1.);
    
    float t0, t1;
    vec3 c0, c1;
    if (rate < 0.5) {
        t0 = 0.0; t1 = 0.5;
        c0 = color1; c1 = color2;
    }
    else if (rate < 0.6) {
        t0 = 0.5; t1 = 0.6;
        c0 = color2; c1 = color3;
    }
    else if (rate < 0.7) {
        t0 = 0.6; t1 = 0.7;
        c0 = color3; c1 = color4;
    }
    else if (rate < 0.8) {
        t0 = 0.7; t1 = 0.8;
        c0 = color4; c1 = color5;
    }
    else {
        t0 = 0.8; t1 = 1.0;
        c0 = color5; c1 = color6;
    }

    float param = (rate - t0) / (t1 - t0);
    color = mix(c0, c1, param);

    //circle only
    if (lengthCenterToUV > 0.278)
        color *= 0.0;

    gl_FragColor = vec4(color, 1.0);
}

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