NiSourceTextureIsExternal
This is a command from NifSE.
Syntax
(bool:isExt) NiSrcTexIsExt short:nifID short:blockID
Returns whether the texture used by the indicated NiSourceTexture-derived block is external or not. The blockID argument, as usual, defaults to 0, indicating the root which is a NiNode block. NiNode blocks are not derived from NiSourceTexture, so this function will almost never be used without specifying the blockID desired.
An external texture is determined entirely from a texture file. Use NiSourceTextureGetFile to get that file. Internal textures still use a texture file, but also uses a variety of internal data structures to modify the texture; the structures are currently not available through NifSE.
Typically, one determines blockID by using NiAVObjectGetPropertyByType to get the NiTexturingProperty associated with a NiAVObject, and then using NiTexturingPropertyGetTextureSource to get the blockID of the NiSourceTexture.