This is 3-pass GLSL preprocess fragment shader used in AR Spark (Facebook messenger AR effects)

Gameboy preprocessor frag shader

varying vec2 hdConformedUV;
varying vec2 uv;
uniform sampler2D inputImage;
uniform int passIndex;
uniform vec2 uRenderSize;
uniform float uTime;
uniform float uPixelRes; // For UI parameters
uniform sampler2D pixelate; //pass 0
uniform sampler2D colorize; //pass 1
uniform sampler2D grid; //pass2
uniform float uTileResolution;

// check floor for right luminosity, maybe exp the luma)

vec4 toYCbCr(vec4 rgb)
{
    rgb = rgb * 255.;
    float r = rgb.r;
    float g = rgb.g;
    float b = rgb.b;
	return vec4(0.299*r+0.587*g+0.114*b,
               128.-0.168736*r-0.331264*g+0.5*b,
               128.+0.5*r-0.418688*g-0.081312*b,
               1.);
}


vec4 toRGB(vec4 ybr)
{
    float y = ybr.x;
    float b = ybr.y;
    float r = ybr.z;
	return vec4(y+1.402*(r-128.),
               y-0.344136*(b-128.)-0.714136*(r-128.),
               y+1.772*(b-128.),
               1.)
        		/255.;
}

float desaturate(vec4 tex, vec2 uv){
 	vec3 col = texture2D(inputImage, uv).xyz;
	return dot(col, vec3(0.3,0.6,0.1));
}


void main()
{    if(passIndex == 0) //pixilate//
     {
      float dx = 15.0 * (1.0 / uPixelRes);
      float dy = 10.0 * (1.0 / uPixelRes);
      vec2 uv_ = uv;
      uv_ = vec2(dx * floor(uv.x / dx), dy * floor(uv_.y / dy));

      gl_FragColor = texture2D(inputImage, uv_);

    } else if (passIndex == 1) //colorize//
    {
      vec3 palette[4];
      float palgray[4];
      vec3 lum = vec3(0.2126,0.7152,0.0722);

      palette[0] = vec3(15,56,15)/256.0;
      palette[1] = vec3(48,98,48)/256.0;
      palette[2] = vec3(139,171,127)/256.0;
      palette[3] = vec3(175,199,81)/256.0;
      for (int i = 0; i < 4; ++i)
          palgray[i] = dot(palette[i], lum);
      for (int i = 0; i < 4; ++i)
          palgray[i] /= palgray[3];


      float gray = dot(texture2D(pixelate, uv.xy).rgb, lum);
      vec3 color;
      for (int i = 0; i < 4; ++i) {
          if (gray <= palgray[i]) {
              color = palette[i];
              break;
          }
      }

      gl_FragColor = vec4(color, 1.);

    } else if (passIndex == 2) //grid//
      {
        vec2 uvsample = floor(uv*uTileResolution)/uTileResolution;

        float ll = toRGB(toYCbCr(texture2D(inputImage, uvsample))).x;

        vec2 uvA = fract(uv*uTileResolution);

        vec4 justcolor = toRGB(vec4(toYCbCr(vec4(texture2D(colorize, uvsample).xyz,1.)).xyz,1.));


        float a;
        vec2 uv2 = uvA * 2. - 1.;
        a = uv2.x * uv2.x + uv2.y * uv2.y;

        float final_ = distance(0.5, uvA.x)+distance(0.5, uvA.y);
        final_ = 1.-length(0.5 - uvA);
        final_ = floor(final_+ll);

      gl_FragColor = vec4(final_)*justcolor;

    } else {

      gl_FragColor = texture2D(grid, uv);
    }

}

Are you able to use this with Spark-AR Studio? or is this a compiled thing that requires x-code?

@pjkarlik

Are you able to use this with Spark-AR Studio? or is this a compiled thing that requires x-code?

Did you get a way to code open GLSL shaders in spark AR ?

in the old Spark (pre version 66) they allowed pre & post processsors to have GLSL shaders. (no longer)