From Divinity Engine Wiki
- query GetSurfaceTypeIndex([in](STRING)_Surface, [out](INTEGER)_Index)
Returns the _Index of a _Surface in the internal numbered list of surface types.
- Success/Failure: Never fails.
- _Index: The index of a surface. Returns -1 if the _Surface does not exist, or if there is no surface.
- This call is mainly useful if you need to handle surfaces in behaviour script and Osiris simultaneously - the SURFACE type in behaviour script can be converted to an integer with this call and then set with SetVarInteger.
- The surface types page lists the surfaces in the same order as they exist in the internal list, starting at -1 for SurfaceNone.