[SM5] /Engine/Generated/Material.ush(1595,12-105): error X3004: undeclared identifier 'GetScreenSpaceData'

Why am I getting this error in my Material editor? I have seen lots of tutorials use this function.

I use it in line :

float ML = GetScreenSpaceData(ViewportUVToBufferUV(ScreenPosition + float2(-offset_h, 0)), false).GBuffer.CustomStencil.r;

Screen space data will not be available to use from custom node, unless you actually use scene texture material expression somewhere in tn material graph.

It’s because I don’t understand shaders very well, can you elaborate on what you mean by having to use the scene texture material expression somewhere?