// #include //ly.img.cesdk/shader/common/ubq_color_conversions
uniform shader image;
uniform float offset;
uniform float darkness;

// Obtaining the nearest value to the predefined HSL levels
float nearestLevel(float col) {
  const int levCount = 6;  // TODO: Include option for the user to choose the amount of levels
  const float interval = 1.0 / float(levCount);

  for (float i = 0.0; i <= 1.0; i += interval) {
    if (col >= i && col <= (i + interval)) {
      return (abs(col - i) < abs(col - (i + interval))) ? i : (i + interval);
    }
  }
  return 0;
}

half4 main(float2 coord) {
  float4 rgba = unpremul(image.eval(coord));
  float3 origCol = rgba.rgb;
  float alpha = rgba.a;

  // Applying the edge detection filter to create an outline

  // Obtaining the local 3x3 matrix
  float4 A[9];
  A[0] = unpremul(image.eval(coord + float2(-1, -1)));
  A[1] = unpremul(image.eval(coord + float2(0, -1)));
  A[2] = unpremul(image.eval(coord + float2(1, -1)));
  A[3] = unpremul(image.eval(coord + float2(-1, 0)));
  A[4] = rgba;
  A[5] = unpremul(image.eval(coord + float2(1, 0)));
  A[6] = unpremul(image.eval(coord + float2(-1, 1)));
  A[7] = unpremul(image.eval(coord + float2(0, 1)));
  A[8] = unpremul(image.eval(coord + float2(1, 1)));

  // Computing the x-direction gradient
  float4 sum_x = -A[0] + (A[2]) - (A[3] * 2.0) + (A[5] * 2.0) - (A[6]) + (A[8]);

  // Computing the y-direction gradient
  float4 sum_y = A[0] + (A[1] * 2.0) + A[2] - A[6] - (A[7] * 2.0) - A[8];

  // Computing the sum
  float4 sum = sqrt((sum_x * sum_x) + (sum_y * sum_y));

  // Combining the colors to obtain a black color for the outline
  float sumLength = length(sum);
  float outlineShade = 1.0 - sumLength;
  float4 outlineCol = float4(outlineShade, outlineShade, outlineShade, alpha);

  // Thresholding
  if (outlineShade > 0.5)
    outlineShade = 1.0;

  // Applying the cel-shading effect
  float3 hslColor = rgb2hsl(origCol);
  hslColor.x = nearestLevel(hslColor.x);
  hslColor.y = nearestLevel(hslColor.y);
  hslColor.z = nearestLevel(hslColor.z);

  float3 outColor = hsl2rgb(hslColor);

  float4 tc = float4(outColor.r, outColor.g, outColor.b, alpha);

  // If pixel is an edge, set pixel to the outline color
  if (outlineShade != 1.0) {
    tc = outlineCol;
  }

  tc.rgb *= tc.a;

  return tc;
}