code/__DEFINES/pipe_construction.dm

PIPE_STRAIGHT	2 directions: N/S, E/W
PIPE_BENDABLE	6 directions: N/S, E/W, N/E, N/W, S/E, S/W
PIPE_TRINARY	4 directions: N/E/S, E/S/W, S/W/N, W/N/E
PIPE_TRIN_M	8 directions: N->S+E, S->N+E, N->S+W, S->N+W, E->W+S, W->E+S, E->W+N, W->E+N
PIPE_UNARY	4 directions: N, S, E, W
PIPE_ONEDIR	1 direction: N/S/E/W
PIPE_UNARY_FLIPPABLE	8 directions: N/S/E/W/N-flipped/S-flipped/E-flipped/W-flipped
PIPE_ONEDIR_FLIPPABLE	2 direction: N/S/E/W, N-flipped/S-flipped/E-flipped/W-flipped

Define Details

6 directions: N/S, E/W, N/E, N/W, S/E, S/W

1 direction: N/S/E/W

2 direction: N/S/E/W, N-flipped/S-flipped/E-flipped/W-flipped

2 directions: N/S, E/W

4 directions: N/E/S, E/S/W, S/W/N, W/N/E

8 directions: N->S+E, S->N+E, N->S+W, S->N+W, E->W+S, W->E+S, E->W+N, W->E+N

4 directions: N, S, E, W

8 directions: N/S/E/W/N-flipped/S-flipped/E-flipped/W-flipped