​

uniform sampler2D p_tex;

uniform sampler2D s_tex;

​

const float N = 600.;

uniform int iFrame;

uniform float dt;

​

const vec2 speed_offset = vec2(0.5, 0.5);

const float boundary_offset = 0.05;

​

​

void main() {

  vec2 uv = gl_FragCoord.xy / vec2(N, 1.);

  // Initial conditions

  if(iFrame < 10) {

    vec2 s = vec2(0.05, 0.2);

    gl_FragColor = vec4(s + speed_offset, 0., 1.);

    return;

  }

  vec2 p = texture2D(p_tex, uv).xy;

  vec2 s = texture2D(s_tex, uv).xy - speed_offset;

  // Collisions

  for(float i = 0.; i < N; ++i) {

    vec2 p_j = texture2D(p_tex, vec2(i/N, 0.5)).xy;

    //if(abs(i/N - uv.x) < 0.001) continue;

    vec2 dir = p - p_j;

    float r = dot(dir, dir);

    if(r < 0.08 && r > 0.00000001) {

      s += 0.00000001*(dir/(r*r))*dt;

    }

  }

  s *= 0.99;

  // Wall collisions

  if(p.y > 1. - boundary_offset || p.y < boundary_offset) {

    s.y *= -1.;

  }

  if(p.x > 1. - boundary_offset || p.x < boundary_offset) {

    s.x *= -1.;

  }

  gl_FragColor = vec4(s + speed_offset, 0., 1.);

}