Shadow error in custom Shader

I got this shader:
I simply tried to add shadows, but now It gets an error:

undeclared identifier ‘ComputeScreenPos’ at line 56 (on d3d11)

The line is


I don’t know how to fix this. please help me.

Works now. Thanks to Namey5.
I added #include “UnityCG.cginc” to my includes
removed the tag “queue” = “transparent”