2D Scaling Pixel Art Fragment Shader (Metal)

2DPixelArtFragmentShader.metal

 fragment float4
 pixelArtFragmentShader(RasterizerData in [[stage_in]],
                        texture2d_array<half> texture_atlas [[ texture(0) ]])
 {
     constexpr sampler textureSampler (mag_filter::linear,
                                       min_filter::linear);
     
     // This is the alpha value from the graph, or the size of the margin where you 
     // want to apply bilinear filtering around a texel
     float2 alpha = float2(0.07);
     
     // As noted in the article, this is x from the graph, or the fractional
     // portion of the (width/height) scaled uv coordinates.
     float2 x = fract(in.vUv);
  
     // xprime is the adjusted fractional portion of the scaled uv coordinate,
     // and it is the value matching the desired output
     float2 xprime = clamp(0.5/(alpha*x), 0.0, 0.5) +
                     clamp((0.5/(alpha*(x - 1.0))) + 0.5, 0.0, 0.5);
 
     // This just maps from our invented coordinate system back to standard
     // uv coordinates
     float2 textureCoordinate = (floor(in.vUv) + xprime)/in.textureSize;
  
     // NOTE: This assumes you are using the first texture in the texture array. Hence 
     // zero for the last parameter. I tend to pass that in with the RasterizerData 
     // struct when working with 2D texture arrays in Metal. 
     const half4 colorSample = texture_atlas.sample(textureSampler, 
                                                    textureCoordinate, 0);
  
     float4 Result = float4(colorSample[0], colorSample[1], 
                            colorSample[2], colorSample[3]);
  
     // return the color of the texture
     return Result;
}