// Name: Shader Art Coding Introduction
// Author: kishimisu
// URL: https://www.shadertoy.com/view/mtyGWy
#version 330 core
precision highp float;

out vec4 FragColor;
in vec2 vUV;
uniform vec2 iResolution;
uniform float iTime;

vec3 palette( float t) {
    vec3 a = vec3(0.5, 0.5, 0.5);
    vec3 b = vec3(0.5, 0.5, 0.5);
    vec3 c = vec3(1.0, 1.0, 1.0);
    vec3 d = vec3(0.263, 0.416, 0.557);
    return a + b * cos( 6.28318 * (c * t * d) );
}

void mainImage( out vec4 fragColor, in vec2 fragCoord )
{
    vec2 uv = (fragCoord * 2.0 - iResolution.xy) / iResolution.y;
    vec2 uv0 = uv;
    vec3 finalColor = vec3(0.0);
    
    for (float i = 0.0; i < 4.0; i++) {
        uv = fract(uv * 1.5) - 0.5;

        float d = length(uv) * exp(-length(uv0));

        vec3 col = palette(length(uv0) + i * 0.4 + iTime * 0.4);

        d = sin(d * 8.0 + iTime) / 8.0;

        d = abs(d);

        d = pow(0.01 / d, 1.2);

        finalColor += col * d;
    }
    
    fragColor = vec4(finalColor, 1.0);
}

void main() {
    vec2 fragCoordPixels = vUV * iResolution;
    vec4 outColor;
    mainImage(outColor, fragCoordPixels);
    FragColor = outColor;
}