Defines line join types.

Values:

IG_VECT_LINEJOIN_MITER	Specifies that the outer edges of the two lines should extend to meet at an angle.
IG_VECT_LINEJOIN_ROUND	Specifies that lines should be joined by a circular arc centered on the join point.
IG_VECT_LINEJOIN_BEVEL	Specifies IG_VECT_LINECAP_BUTT endpoint styles.