thebookofshaders/examples/07/randj063-animated.frag

// By Jaskirat Randhawa ( http://jaskirat.me/ ) 
// For Shader Studio Course https://github.com/patriciogonzalezvivo/ss2015

#ifdef GL_ES
precision mediump float;
#endif

#define TWO_PI 6.28318530718

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

vec3 circle ( float posX, float posY, float rad, vec3 color){
    vec2 st = gl_FragCoord.xy/u_resolution;
    // st -=.5;
    st.x -=posX;
    st.y -=posY;
    float pct = 1. - length(st)*2.*rad;
    // rad = 1./rad;
    // pct = fract(pct*1.);
    pct = step(.997,pct);

    color = vec3(pct)*color;
    
    return color;
}

void main(){
    
    vec3 color = vec3(0.0);
    vec3 color1 = vec3(.5,.8,.1);
    vec3 color2 = vec3(.9,.4,.4);
    vec3 color3 = vec3(.2,.8,.8);
    vec3 c1= vec3(0);
    for(float i = 0.; i<20. ; i++){
        c1 += circle( sin(.4*i*u_time/2.),cos(.3*i*u_time),.1,color1);
        c1 += circle( sin(.2*i*u_time),cos(.1*i),.1,color2);    
        c1 += circle( sin(.2*i*u_time/2.),cos(.6*i*u_time/2.),.1,color3);
    }
    // c1 = circle( .5,.5,.1,color1);
    // c1 += circle( .2,.5,.1,color2);
    // c1 += circle( .5,.4,.1,color3);
    
    // c1 += circle( sin(u_time)/2.+.5, cos(u_time)/2.+.5,1.1);
    // c1 += circle( sin(u_time+5.)/2.+.5, cos(u_time+5.)/2.+.5,1.1);
    

    // color = vec3(c1);
    // color *= color1;
    gl_FragColor = vec4(c1,1.0);
}