Pixling World flow shader

float flowEffect(vec2 texcoord, sampler2DArray source, int sourceLayer, int groundLayer, vec2 texelSize, float amount) {
  float v0 = texture(source, vec3(texcoord + vec2(-texelSize.x, -texelSize.y), sourceLayer)).r;
  float v1 = texture(source, vec3(texcoord + vec2(0, -texelSize.y), sourceLayer)).r;
  float v2 = texture(source, vec3(texcoord + vec2(texelSize.x, -texelSize.y), sourceLayer)).r;
  
  float v3 = texture(source, vec3(texcoord + vec2(-texelSize.x, 0), sourceLayer)).r;
  float v4 = texture(source, vec3(texcoord + vec2(0, 0), sourceLayer)).r;
  float v5 = texture(source, vec3(texcoord + vec2(texelSize.x, 0), sourceLayer)).r;

  float v6 = texture(source, vec3(texcoord + vec2(-texelSize.x, texelSize.y), sourceLayer)).r;
  float v7 = texture(source, vec3(texcoord + vec2(0, texelSize.y), sourceLayer)).r;
  float v8 = texture(source, vec3(texcoord + vec2(texelSize.x, texelSize.y), sourceLayer)).r;

  float g0 = 0.0;
  float g1 = 0.0;
  float g2 = 0.0;
  float g3 = 0.0;
  float g4 = 0.0;
  float g5 = 0.0;
  float g6 = 0.0;
  float g7 = 0.0;
  float g8 = 0.0;

  if (groundLayer >= 0) {
    g0 = texture(source, vec3(texcoord + vec2(-texelSize.x, -texelSize.y), groundLayer)).r;
    g1 = texture(source, vec3(texcoord + vec2(0, -texelSize.y), groundLayer)).r;
    g2 = texture(source, vec3(texcoord + vec2(texelSize.x, -texelSize.y), groundLayer)).r;

    g3 = texture(source, vec3(texcoord + vec2(-texelSize.x, 0), groundLayer)).r;
    g4 = texture(source, vec3(texcoord + vec2(0, 0), groundLayer)).r;
    g5 = texture(source, vec3(texcoord + vec2(texelSize.x, 0), groundLayer)).r;

    g6 = texture(source, vec3(texcoord + vec2(-texelSize.x, texelSize.y), groundLayer)).r;
    g7 = texture(source, vec3(texcoord + vec2(0, texelSize.y), groundLayer)).r;
    g8 = texture(source, vec3(texcoord + vec2(texelSize.x, texelSize.y), groundLayer)).r;
  }

  float gv0 = g0 + v0;
  float gv1 = g1 + v1;
  float gv2 = g2 + v2;
  float gv3 = g3 + v3;
  float gv4 = g4 + v4;
  float gv5 = g5 + v5;
  float gv6 = g6 + v6;
  float gv7 = g7 + v7;
  float gv8 = g8 + v8;

  float vCenter = v4;
  float gCenter = g4;
  float gvCenter = gv4;
  float v = vCenter;

  float d0 = gv0 - gvCenter;
  float d1 = gv1 - gvCenter;
  float d2 = gv2 - gvCenter;
  float d3 = gv3 - gvCenter;
  float d4 = gv4 - gvCenter;
  float d5 = gv5 - gvCenter;
  float d6 = gv6 - gvCenter;
  float d7 = gv7 - gvCenter;
  float d8 = gv8 - gvCenter;

  v += (d0 > 0.0 ? min(d0 * amount, v0) : -min(-d0 * amount, vCenter)) / 8.0;
  v += (d1 > 0.0 ? min(d1 * amount, v1) : -min(-d1 * amount, vCenter)) / 8.0;
  v += (d2 > 0.0 ? min(d2 * amount, v2) : -min(-d2 * amount, vCenter)) / 8.0;
  v += (d3 > 0.0 ? min(d3 * amount, v3) : -min(-d3 * amount, vCenter)) / 8.0;
  v += (d4 > 0.0 ? min(d4 * amount, v4) : -min(-d4 * amount, vCenter)) / 8.0;
  v += (d5 > 0.0 ? min(d5 * amount, v5) : -min(-d5 * amount, vCenter)) / 8.0;
  v += (d6 > 0.0 ? min(d6 * amount, v6) : -min(-d6 * amount, vCenter)) / 8.0;
  v += (d7 > 0.0 ? min(d7 * amount, v7) : -min(-d7 * amount, vCenter)) / 8.0;
  v += (d8 > 0.0 ? min(d8 * amount, v8) : -min(-d8 * amount, vCenter)) / 8.0;

  return v;
}