////////////////////////////////////////////////////////////////////////////////////////////////////////////

float emboss = 0.5;
int steps = 8;
float fade = 1.;

// play with these parameters to custimize the effect
// ===================================================

//speed
const float speed = 0.2;
const float speed_x = 0.3;
const float speed_y = 0.3;

float time_ = iTime * 1.3;
float time_speed = time_ * speed;
float time_speed_x = time_ * speed_x;
float time_speed_y = time_ * speed_y;

// refraction
float emboss_ = emboss * fade;
const float intensity = 2.4;
const float frequency = 6.0;
const int angle = 7; // better when a prime
const float delta_theta = 0.8975979010256551; // 2.0 * PI / float(angle);

int steps_ = steps;

// reflection
const float delta = 60.;
const float intence = 700.;

const float reflectionCutOff = 0.012;
const float reflectionIntence = 200000.;

// ===================================================

  float col(vec2 coord)
  {
    float col = 0.0;
    float theta = 0.0;
    for (int i = 0; i < steps_; i++)
    {
      vec2 adjc = coord;
      theta = delta_theta*float(i);
      adjc.x += cos(theta)*time_speed + time_speed_x;
      adjc.y -= sin(theta)*time_speed - time_speed_y;
      col = col + cos( (adjc.x*cos(theta) - adjc.y*sin(theta))*frequency)*intensity;
    }

    return cos(col);
  }

//---------- main

void mainImage( out vec4 fragColor, in vec2 fragCoord ) {
    vec2 p = fragCoord / iResolution.xy, c1 = p, c2 = p;
    float cc1 = col(c1);

    c2.x += iResolution.x/delta;
    float dx = emboss_*(cc1-col(c2))/delta;

    c2.x = p.x;
    c2.y += iResolution.y/delta;
    float dy = emboss_*(cc1-col(c2))/delta;

    c1.x += dx*2.;
    c1.y = c1.y+dy*2.;

    float alpha = 1.+dot(dx,dy)*intence;
        
    float ddx = dx - reflectionCutOff;
    float ddy = dy - reflectionCutOff;
    if (ddx > 0. && ddy > 0.)
        alpha = pow(alpha, ddx*ddy*reflectionIntence);
        
    vec4 col = texture2D(iChannel[0], c1)*(alpha);
    fragColor = col;
}

////////////////////////////////////////////////////////////////////////////////////////////////////////////

void main() {
    mainImage(gl_FragColor, gl_FragCoord.xy);
}