int hedge_presrcvertex(<geometry>geometry, int hedge)
When running in the context of a node (such as a wrangle SOP), this argument can be an integer representing the input number (starting at 0) to read the geometry from.
Alternatively, the argument can be a string specifying a geometry file (for example, a
.bgeo) to read from. When running inside Houdini, this can be an
The vertex number of the vertex that comes before the source vertex of the
hedge in the primitive that contains
-1 if the half-edge is not valid.
int presrcvtx; // Get the pre-source vertex of half-edge number 3. presrcvtx = hedge_presrcvertex("defgeo.bgeo", 3);