//This function will compute a block's UV given a block's normal in world coordinates and it's world position.
void ComputeBlockUV(inout float3 normal, float4 worldPos, out float2 uv0, out float4 dxdy)
{
  float3 dx = ddx(worldPos.xyz);
  float3 dy = ddy(worldPos.xyz);
  normal = normalize(cross(dy, dx));

  if(normal.x > 0.5)
    {
      uv0 = frac(float2(-worldPos.z, -worldPos.y));
      dxdy = float4(dx.zy, dy.zy);
    }

  if(normal.x < -0.5)
    {
      uv0 = frac(float2(worldPos.z, -worldPos.y));
      dxdy = float4(dx.zy, dy.zy);
    }
  //top

  if(normal.y > 0.5)
    {
      uv0 = frac(worldPos.xz);
      dxdy = float4(dx.xz, dy.xz);
    }

  //bottom
  if(normal.y < -0.5)
    {
      uv0 = frac(float2(-worldPos.x, worldPos.z));
      dxdy = float4(dx.xz, dy.xz);
    }

  if(normal.z > 0.5)
    {
      uv0 = frac(float2(worldPos.x, -worldPos.y));
      dxdy = float4(dx.xy, dy.xy);
      //uv0 = float2(In.worldPos.x, -In.worldPos.y);
    }
  if(normal.z < -0.5)
    {
      uv0 = frac(float2(-worldPos.x,-worldPos.y));
      dxdy = float4(dx.xy, dy.xy);
    }
}