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. |