julia feathers.sksl

uniform float2 iResolution;
uniform float iTime;
uniform float4 iMouse;

// julia feathers 
// Created by sympou in 2022-05-03
// https://www.shadertoy.com/view/slfBD2

const float tau = 6.28; 

mat2 rot(float a) {
    return mat2(
        cos(a), sin(a),
        -sin(a), cos(a)
);}
vec4 main( in vec2 fragCoord )
{
    float zoom = .75;
    vec2 u1 = (2.*fragCoord - iResolution.xy)/iResolution.y;
    u1 *= zoom; //exp(-zoom);

	vec2 mouse = iMouse.xy/iResolution.xy*2.-1.;
    
    if (mouse.x == -1.0 && mouse.y == -1.0) mouse = vec2(-0.26,0.85); 

    float val = 0.; 

    //loop (originally i < 64)
    for(float i = 0.; i < 15.; i++){
            
        u1 = mouse + vec2(u1.x*u1.x - u1.y*u1.y,2.*u1.x*u1.y);       
        vec2 u2 = u1*rot(3.1415692*(iTime*0.5+i));
        
        if (u2.y >= 8.) {
            val += 0.01 + i/64. +  1./u2.y;
        }
      	if (val!=0.) break;
    }
    
    
    vec3 col = 0.5 + 0.5*cos(tau*(val+.4+vec3(.0,.1,.2)));

    // Output to screen
    return( vec4(col,1.0));
}