#ifdef GL_ES
precision highp float;
#extension GL_OES_standard_derivatives : enable
#endif

uniform float time;
uniform vec2 mouse;
uniform vec2 resolution;
varying vec2 surfacePosition;
 
#define mouse vec2(.5 + 0.1*cos(time*3.+surfacePosition.x*4.+cos(time*3.+surfacePosition.x*4.)), 0.)

// afl_ext 2017

#define EULER 2.7182818284590452353602874
#define IEULER 0.367879

#define time mouse.x
float wave(vec2 uv, vec2 emitter, float speed, float phase, float timeshift){
	float dst = distance(uv, emitter);
	return pow(EULER, sin(dst * phase - (time + timeshift) * speed));
}
vec2 wavedrag(vec2 uv, vec2 emitter){
	return normalize(uv - emitter);
}
float getwaves(vec2 position){
    float iter = 0.0;
    float phase = 6.0;
    float speed = 2.0;
    float weight = 1.0;
    float w = 0.0;
    float ws = 0.0;
    float iwaterspeed = 6.0;
    for(int i=0;i<24;i++){
        vec2 p = vec2(sin(iter), cos(iter)) * 300.0;
        float res = wave(position, p, speed, phase, 0.0) * IEULER;
        float res2 = wave(position, p, speed, phase, 0.006) * IEULER;
        position -= wavedrag(position, p) * (res - res2) * weight * 5.0 * iwaterspeed;
        w += res * weight;
        iter += 12.0;
        ws += weight;
        weight = mix(weight, 0.0, 0.12);
        phase *= 1.2;
        speed = pow(speed, 1.014);
    }
    return w / ws;
}

void main( void ) {	
	float w = getwaves(surfacePosition);
	gl_FragColor = vec4( 1.0 - w*vec4(.88-w*.25,1.2,1.3,0.)*1.5 );
}