artist-vap-find-endpoint is a compiled Lisp function in `artist.el'.

(artist-vap-find-endpoint X1 Y1 STEP-X STEP-Y ACCEPT-SET REJECT-SET)

Find one endpoint for line through X1, Y1.
The endpoint is searched for in the direction defined by STEP-X, STEP-Y,
accepting characters in the list ACCEPT-SET, stopping immediately
when finding characters in the list REJECT-SET. Fuzziness, that is
the number of consecutive characters not in ACCEPT-SET to allow as
part of the line, is determined by the variable `artist-vaporize-fuzziness'.
An endpoint is a cons pair, (ENDPOINT-X . ENDPOINT-Y).