2D Scaling Pixel Art Vertex Shader (Metal)

2dpixelartshader.metal

typedef enum MacVertexInputIndex
{
  MacVertexInputIndexVertices = 0,
  MacVertexInputIndexViewportSize = 1,
  MacVertexInputIndexTextureSize = 2
} MacVertexInputIndex;

vertex RasterizerData         
vertexShader(uint vertexID [[ vertex_id ]],                                  
             constant MacTextureShaderVertex *vertexArray [[ buffer(MacVertexInputIndexVertices) ]],
             constant vector_uint2 *viewportSizePointer  [[ buffer(MacVertexInputIndexViewportSize) ]],
             constant MacTextureSize *textureSize [[buffer(MacVertexInputIndexTextureSize) ]])
{                                                                                                     
  RasterizerData out;                                                                         
  
  // Index into the array of positions to get the current vertex.
  // Positions are specified in pixel dimensions (i.e. a value of 100 is 100 pixels from
  // the origin)
  float2 pixelSpacePosition = vertexArray[vertexID].position.xy;     
                                                    
  // Get the viewport size and cast to float.
  float2 viewportSize = float2(*viewportSizePointer);                                                    
                                                                                      
  // To convert from positions in pixel space to positions in clip-space,
  //  divide the pixel coordinates by half the size of the viewport.
  // Z is set to 0.0 and w to 1.0 because this is 2D sample.   
  out.position = vector_float4(0.0, 0.0, 0.0, 1.0);
                                                         
  // NOTE: (Ted)  This would be the Open GL equivalent of mapping the projection matrix to
  //              the game's screen coordinates. This is a 2D game.
  out.position.xy = (pixelSpacePosition / (viewportSize / 2.0)) - 1;
                                                                      
  out.textureCoordinate = vertexArray[vertexID].textureCoordinate;
                                                                    
  out.textureSize = float2(textureSize->Width, textureSize->Height);
  
  out.vUv = out.textureSize*out.textureCoordinate;
                                                                                                                                                                                 
  return out;                                    
}