precision mediump float;

// I'M MISSING the modulo operator, but otherwise that's basically it.

​

// lets grab texcoords just for fun

varying vec2 vTexCoord;

​

uniform float iResolutionX;

uniform float iResolutionY;

​

const float eps = 0.01;

const int N = 10;

// our texture coming from p5

uniform sampler2D tex0;

​

​

void main() {

​

  vec2 uv = vTexCoord;

  uv = 1.0 - uv;

  vec2 pw = vec2(1. / iResolutionX, 1. / iResolutionY);

​

  vec4 tex = texture2D(tex0, uv);

  vec2 v3 = vec2(3, 0) * pw.y;

  vec2 v2 = vec2(2, 0) * pw.y;

  vec2 v1 = vec2(1, 0) * pw.y;

  vec2 h3 = vec2(0, 3) * pw.x;

  vec2 h2 = vec2(0, 3) * pw.x;

  vec2 h1 = vec2(0, 3) * pw.x;

  vec4 C[16];

  // UP

  C[0] = texture2D(tex0, uv - h1 + v3);

  C[1] = texture2D(tex0, uv      + v3);

  C[2] = texture2D(tex0, uv + h1 + v3);

  // Top Right Corner

  C[3] = texture2D(tex0, uv + v2 + h2);

  // Right

  C[4] = texture2D(tex0, uv + v1 + h3);

  C[5] = texture2D(tex0, uv      + h3);

  C[6] = texture2D(tex0, uv - v1 + h3);

​

  // Bottom Right Corner

  C[7] = texture2D(tex0, uv - v2 + h2);

  // Bottom

  C[8]  = texture2D(tex0, uv - h1 - v3);

  C[9]  = texture2D(tex0, uv      - v3);

  C[10] = texture2D(tex0, uv + h1 - v3);

  // Bottom Left Corner

  C[11] = texture2D(tex0, uv - v2 - h2);

  // Left

  C[12] = texture2D(tex0, uv + v1 - h3);

  C[13] = texture2D(tex0, uv      - h3);

  C[14] = texture2D(tex0, uv - v1 - h3);

  // Top Left Corner

  C[15] = texture2D(tex0, uv + v2 - h2);

  float C_grey[16];

  for(int i = 0; i < 16; ++i) {

    C_grey[i] =  (C[i].r + C[i].g + C[i].b) / 3.;

  }

  float center_grey =  (tex.r + tex.g + tex.b) / 3.;

  float diff;

  for(int i = 0; i < 16; ++i) {

    int curr = 0;

    if(C_grey[i] > center_grey + eps) {

      diff = 0.;

      for(int j = 1; j < 16; ++j) {

        int k = i + j;

        if(k > 15) break;

        if(C_grey[i + j] < center_grey + eps) break;

        diff += C_grey[i + j]  - center_grey;

        curr += 1;

      }

    } else if(C_grey[i] < center_grey - eps) {

      diff = 0.;

      for(int j = 1; j < 16; ++j) {

        int k = i + j;

        if(k > 15) break;

        if(C_grey[i + j] > center_grey - eps) break;

        diff += center_grey - C_grey[i + j];

        curr += 1;

      }

    }

    if(curr > N) {

      gl_FragColor = vec4(0.0, diff / float(N), 0.0, 1.0);

      return;

    }

  }

  gl_FragColor = vec4(0., 0., 0., 1.0);;

}