How to get PostProcessInput0 in an HLSL Custom Material Node?

I’m trying to write a postprocessing material that applies a Gaussian blur to the scene. I’m trying use a custom node, similar to the node described here: Gaussian blur post processing material

The problem comes with the Texture2DSample. I’m told that PostprocessInput0 doesn’t exist. I think it’s been changed to PPI_PostProcessInput0, but when I use that, I’m told that PPI_PostProcessInput0Sampler doesn’t exist.

How do I access PostProcessInput0 in a Texture2DSample?

Edit: Even though a SceneTexture:PostProcessInput0 node outputs a color, if you make an input to your custom node called SceneTexture and connect the output of SceneTexture:PoostProcessInput0, you then have access to SceneTextureLookup and GetDefaultScentTextureUV functions. Use the SceneTextureLookup insteadof Texture2DSample. the index for PostProcessInput0 is a constant, PPI_PostProcessInput0.
I was confused because if you don’t connect the SceneTexture node to your custom node, the compiler can’t find the SceneTextureLookup function.