If there's a wall on the left, we draw the part where it hits the ceiling and the floor:
216 IF LEFT = 1 OR LEFT = 3 OR LEFT = 4 THEN HPLOT L1,T1 TO L2,T2: HPLOT L1,B1 TO L2,B2
And likewise the right:
218 IF RIGH = 1 OR RIGH = 3 OR RIGH = 4 THEN HPLOT R1,T1 TO R2,T2: HPLOT R1,B1 TO R2,B2
If there's a 4 on the left (we still don't know what 4 is) we draw most based on LD%:
220 IF LEFT = 4 AND DIS > 0 THEN HPLOT LD%(DIS,0),LD%(DIS,4) TO LD%(DIS,0),LD%(DIS,2) TO LD%(DIS,1),LD%(DIS,3) TO LD%(DIS,1),LD%(DIS,5)
222 IF LEFT = 4 AND DIS = 0 THEN HPLOT 0,LD%(DIS,2) - 3 TO LD%(DIS,1),LD%(DIS,3) TO LD%(DIS,1),LD%(DIS,5)
And similarly on right, but mirror image:
224 IF RIGH = 4 AND DIS > 0 THEN HPLOT 279 - LD%(DIS,0),LD%(DIS,4) TO 279 - LD%(DIS,0),LD%(DIS,2) TO 279 - LD%(DIS,1),LD%(DIS,3) TO 279 - LD%(DIS,1),LD%(DIS,5)
226 IF RIGH = 4 AND DIS = 0 THEN HPLOT 279,LD%(DIS,2) - 3 TO 279 - LD%(DIS,1),LD%(DIS,3) TO 279 - LD%(DIS,1),LD%(DIS,5)
We need to draw some extra lines if we're not a WALL (or 3 or 4):
228 IF LEFT = 3 OR LEFT = 1 OR LEFT = 4 THEN 234
If the distance we're drawing is not zero, we draw a vertical line on the left:
230 IF DIS < > 0 THEN HPLOT L1,T1 TO L1,B1
and regardless of distance we draw another trapezoid:
232 HPLOT L1,T2 TO L2,T2 TO L2,B2 TO L1,B2
and we do the same for the right:
234 IF RIGH = 3 OR RIGH = 1 OR RIGH = 4 THEN 240
236 IF DIS < > 0 THEN HPLOT R1,T1 TO R1,B1
238 HPLOT R1,T2 TO R2,T2 TO R2,B2 TO R1,B2