Blind spots in Doom reject tables

From DoomWiki.org

This analysis is based on the stock REJECT lumps in the Ultimate Doom IWAD, and the same lumps rebuilt using RMB 3.0 with the -perfect option. A "blind spot" is defined as any bit which is 1 in the first file but 0 in the second file. Since RMB ignores all height differences between sectors, many of these can be justified as speed optimizations or as tweaks to match the "3D" topography of the level, but certain cases do produce unintentional special effects, as in E1M6.

No anomalies are present in E2M8: Tower of Babel, E3M1: Hell Keep, E3M8: Dis, or E4M7: And Hell Followed. The latter is most likely a result of the mapper, John "Dr Sleep" Anderson, using RMB himself to build the reject table.

Explanation[edit]

A REJECT table is used by Doom to simplify line-of-sight checking when testing if a monster should see the player and wake up, or if the monster can try and use a ranged attack against the player. A "blind spot" in the REJECT table typically means that two sectors are incorrectly marked as not being visible from one another, making monsters in one sector unable to see actors in the other sector.

This can provide an advantage to the player; as long as they are in one sector and the monster is in the other one, the "blindness" prevents the monster from being woken up, or from attacking the player. In practice, as seen below, in most cases the advantage is negligible.

E1M1: Hangar[edit]

Sectors Effect on gameplay
1 ↔ 79 Very minor. No monsters can enter the courtyard, so 1 → 79 is irrelevant. 79 → 1 is a reasonable approximation given the height difference and the fact that all but a tiny corner of sector 79 is blocked by the wall of the passage. If a shotgun guy closes on the player by entering that tiny corner, they very soon find themselves in sector 6, which is not rejected.
6 ↔ 15 Negligible. The height difference prevents targeting a humanoid opponent in the computer room. It would be possible for a monster to fire from the extreme southwest of the computer room and barely clear the top step of the secret passage, but only if the player stood at the farthest corner of sector 6 (and, in the case of a zombie, only if it shot straight). Conceivably, this may be left over from previous releases of the map, which had a solid wall between the two locations.
6 ↔ 21 None, since sector 21 cannot be entered by players or monsters. Conceivably, this may be left over from previous releases of the map, which had a solid wall between the two locations.
11 ↔ 58 None, since both sectors are inaccessible to monsters.
13 ↔ 58 None, since both sectors are inaccessible to monsters.
15 ↔ 79 Less than in the 6 ↔ 15 case. A player or monster must be in the extreme southwest corner of sector 79 for there to be any (2D) sight lines between it and the computer room; even then, the above reasoning applies. Conceivably, this may be left over from previous releases of the map, which had a solid wall between the two locations.
51 ↔ 53 Negligible. Monsters cannot enter sector 51, and can enter sector 53 only at the southern edges (via the cage or linedef 194). In theory, a player who circlestrafes for an extended period in the zig-zag room benefits once or twice, as a monster happens to wander into that sector and then happens to call P_CheckSight just as the player passes through the southwest corner of the room, but presumably the damage caused by the slime would outweigh such gains. (Tyson competitors have been known to circlestrafe in the zig-zag room briefly.)
51 ↔ 58 None, since both sectors are inaccessible to monsters.
56 ↔ 70 Very minor. The imp in the exit room almost always gets through the door by the time the player has returned to sector 56. A player trying to outrun monsters to the exit might gain some protection as the monsters slowly navigate the walkway, but scarcely more than is already available by hiding around the corner inside the exit room.
57 ↔ 70 Negligible. Monsters cannot enter sector 57, and the above reasoning for 56 ↔ 70 applies even more strongly because the player takes damage while standing there.
64 ↔ 70 Minor. The imp at the exit is vulnerable, briefly, if the player opens the door and then leaps straight back into sector 64. However, any player with such competent footwork could probably also outdraw one imp at short range. A player trying to outrun monsters to the exit might gain some protection as the nearest pursuers cross between the fences, but scarcely more than is already available by hiding around the corner inside the exit room.


E1M2: Nuclear Plant[edit]

Sectors Effect on gameplay
2 ↔ 29 None. The lower windowsill is 72 units above the floor of the courtyard, which makes sighting a humanoid opponent impossible.
3 ↔ 29 None, since sector 3 cannot be entered by players or monsters.
24 ↔ 90 None. The low ceiling in sector 38 blocks all sight lines between the two corners.
24 ↔ 153 None. The overhanging ceiling in sector 36 blocks all sight lines to and from the step.
24 ↔ 154 None. The overhanging ceiling in sector 36 blocks all sight lines to and from the step.
36 ↔ 154 About half the corridor is viewable from some part of the step, which creates a small but observable anomaly. If the player runs to this step and stops, pursuing monsters cannot attack until they themselves reach the stairs; on the other hand, many have already been halted by the red door or by linedef 141, and a stationary player is more vulnerable to the monsters attacking from the north. If the player is in sector 36, monsters descending toward him do not fire while on this step; on the other hand, it is only 40 units wide on average (a zombieman can cross in 20 tics, an imp in 15 tics).
62 ↔ 69 More than half of the step is viewable from the landing, but in fact this is unlikely to have tactical application. If a monster closes on the player by entering the central area of sector 62, it soon finds itself in sector 66, which is not rejected. A player fleeing pursuing monsters might gain some temporary protection as they reach the top of the staircase, but hardly more than is already available by rounding the corner toward the key. Also, a tiny corner of each sector can be mutually sighted through the windows (sectors 74 and 67) across the courtyard, but a monster must wander quite far from the optimal route toward the player in order to be shot there.
62 ↔ 82 Very minor. Only a tiny sliver of each sector is visible along the stairwell (none through the windows), and the above reasoning for 62 ↔ 69 applies to those slivers.
87 ↔ 188 Very minor. Sector 188 of course cannot be entered at all unless the secret door opens; even then, only a small slice of each area is relevant (so small that the protruding corners in sector 183 would block an imp fireball). This therefore seems a defensible optimization.
123 ↔ 139 None. The height of the lift prevents targeting a humanoid opponent in either location.
135 ↔ 138 Negligible. The imp on the blue ledge cannot ascend the staircase, so there is probably no way to lead a monster into sector 135 and then return to sector 138 without exposing oneself to more attacks than one hopes to avoid. In theory, the player can wait in sector 135 for monsters to ascend the lift, then make them momentarily vulnerable by repeatedly lunging to the door and back again (they cannot open it themselves because linedef 728 has the "secret" flag set), but any player with the requisite footwork and snap shooting ability could easily approach that room in a more straightforward way, e.g. by retreating to the slime walkway and chaingun tapping.
141 ↔ 151 Negligible. The height difference prevents targeting a humanoid opponent in sector 141. In theory, the player can occupy a small area in the southwest of sector 141 (not behind the partition, obviously, but right next to it) and prevent attacks by opponents on this step. Presumably, however, since sector 141 is a damaging floor, and since there is nothing to stop said monsters from simply proceeding up the stairs, the player is better advised to take cover by running east along the slime walkway.
141 ↔ 152 Negligible. The above reasoning for 141 ↔ 151 applies here also.


E1M3: Toxin Refinery[edit]

Sectors Effect on gameplay
31 ↔ 54 Very minor. The imp in sector 54 almost always gets through the doorway by the time the player has opened and entered the large trap. In theory, the player is briefly protected if they trigger the large trap and then jump back into the small one, but scarcely more than they would be if they simply continued into the northeast corner of sector 54.
35 ↔ 46 None. The height of the interposing crenel (sector 41) prevents targeting a humanoid opponent in either area.
35 ↔ 47 None; see the above entry for 35 ↔ 46.
60 ↔ 72 Negligible. Monsters cannot enter sector 72. If the player goes to the upper corner of sector 72, thus creating a line of sight to sector 60, monsters are highly unlikely to enter sector 60: the back side has a locked door (sector 61), and they are quite capable of approaching the player by cutting across the nukage pool (sector 58).
70 ↔ 83 Very minor. Monsters cannot enter sector 83, and they have trouble entering sector 70 since they cannot open the secret door (sector 73). If the player goes to sector 83, the height difference and the green pillar block most sight lines to sector 70; a monster who lingers at the western edge cannot attack, but will sooner or later approach the player by entering sector 75, which is not rejected.
109 ↔ 122 Very minor. A small corner of each sector is viewable, wide enough that imp fireballs would not be blocked by interposing corners in the stairwell. In the surrounding chaos, however (on Ultra-Violence, the player awakens at least 30 enemies before reaching this intersection), the occasional misfire presumably goes unnoticed during normal play. Also, there are no linedef flags to stop monsters from simply proceeding toward the stairs.


E1M4: Command Control[edit]

Sectors Effect on gameplay
1 ↔ 32 Very minor. Only two small regions in the back corners of sector 32 are relevant, and the only ranged attacks from the yellow key area will be imp fireballs, which may or may not hit the interposing corners or the stanchion on the landing (southeast corner of sector 35).
6 ↔ 120 Minor. Only a small region in the southwest corner of sector 120 is relevant, but sector 6 is wide enough that a monster crossing toward the player may be vulnerable for a brief period.
12 ↔ 19 Negligible. The line of sight is so narrow, and so hedged about by solid walls, that its absence is unlikely to be noted.
16 ↔ 37 Negligible. Monsters cannot enter sector 16, nor can they open the locked door between the two (sector 41), so either a multiplayer game or ludicrously exacting timing would be required.
33 ↔ 42 Negligible. Monsters cannot enter sector 42, and the player takes damage while there. Moreover, only a narrow wedge near the stairs is relevant, because of the angle through the window (sector 45), and because the interposing landing (sector 35) blocks all sight lines to and from the northern area of sector 42.
37 ↔ 48 Negligible, similarly to 16 ↔ 37 above. Although players and monsters can enter sector 48, it is quite narrow (monsters will wander back out, while players will be mindful of the slime below).
49 ↔ 57 Negligible. Monsters cannot enter sector 57. In principle, a player fleeing pursuing monsters into the exit room is shielded, but only transiently, whereas there are no objects inside and the exit switch is immediately to hand.
77 ↔ 129 77 → 129 affects quite a large fraction of the blue armor room, and so can be exploited during normal play by approaching that room from the west (though the zombies on the ledge are of course unaffected). 129 → 77 is a similar situation to 154 → 36 on E1M2, with the added caveat that the barrel obstructs most of the northern half of the step unless destroyed.
81 ↔ 93 Major. The monsters on the blue ledge are unable to leave it, so they can be shot without retaliation. Less dramatically, monsters refuse to attack a player on the ledge while they approach through the green passage.
85 ↔ 120 Negligible; only affects a miniscule corner of each sector, and then only while both blue key doors are open (sectors 106 and 138).
97 ↔ 113 Major. 97 → 113, 97 → 116, 97 → 117, 121 → 113, 121 → 116, 121 → 117, 119 → 113, 119 → 116, and 119 → 117 together provide the player quite a broad swath of target practice in the barrel room. The area of the stair sectors is smaller, but the effect is still exploitable in the opposite direction, because the stairs are too steep for a monster to descend while cutting the corner.
97 ↔ 116 See 97 ↔ 113 above.
97 ↔ 117 See 97 ↔ 113 above.
103 ↔ 111 None. The height of the interposing lift exit (sector 115) makes targeting a humanoid opponent impossible.
103 ↔ 120 Very minor. Only a narrow slice of each sector is affected, and the blue key door (sector 106), which cannot be opened by monsters, is usually in between.
113 ↔ 119 See 97 ↔ 113 above.
113 ↔ 121 See 97 ↔ 113 above.
116 ↔ 119 See 97 ↔ 113 above.
116 ↔ 121 See 97 ↔ 113 above.
117 ↔ 119 See 97 ↔ 113 above.
117 ↔ 121 See 97 ↔ 113 above.


E1M5: Phobos Lab[edit]

Sectors Effect on gameplay
5 ↔ 9 9 → 5 is easily exploited by opening the outer door (sector 6) and firing in through the window — provided that the player can get through the crowd to the secret area in the first place. 5 → 9 is far less important: a monster would not enter sector 5 except in a highly contrived situation, since both entrances are flagged as secret doors.
5 ↔ 19 None. The height of the interposing window sill (sector 11) prevents targeting a humanoid opponent in either location.
7 ↔ 9 Major; see 5 ↔ 9 above.
7 ↔ 19 Major; see 5 ↔ 9 above.
18 ↔ 28 Major. The imp in sector 28 can be killed without retaliation. A player attacking from sector 28 is invisible to monsters on 6 of the 17 total stairs (see below), so the effect is somewhat counteracted if a large crowd is present.
26 ↔ 28 See 18 ↔ 28 above.
27 ↔ 28 See 18 ↔ 28 above.
28 ↔ 43 See 18 ↔ 28 above.
28 ↔ 44 See 18 ↔ 28 above.
28 ↔ 45 See 18 ↔ 28 above.
49 ↔ 54 Very minor. Monsters cannot normally enter sector 49, since both entrances are flagged as secret doors. A player in sector 49 would notice a misfire only once in a great while, since the affected area of sector 54 (the southeast corner) is not along the direct approach from any other sector.
82 ↔ 106 Negligible. Sector 82 is a portal which remains closed until the player hits the switch in the western area. Even then, only a narrow sliver of each sector is affected; in between them are a locked door (sector 109) and a secret door which cannot be opened until the level is nearly completed (sector 141).
90 ↔ 93 Negligible. A monster will enter one of these sectors only if deliberately lured there through the secret door (sector 64). The player has no good reason to do this because sector 90 is a damaging floor, and would be protected only for a small interval anyway, because only the easternmost end of sector 93 is relevant.


E1M6: Central Processing[edit]

Sectors Effect on gameplay
0 ↔ 24 None. The height of the guard rail on the balcony (sector 23) prevents targeting a humanoid opponent in either location.
24 ↔ 34 None; see 0 ↔ 24 above.
24 ↔ 41 None; see 0 ↔ 24 above.
24 ↔ 57 None; see 0 ↔ 24 above.
125 ↔ 155 Negligible; only a miniscule sliver of each sector is affected, and the fence texture at the start area (linedef 1109) makes aiming more difficult.
125 ↔ 157 Negligible. The reasoning of 125 ↔ 155 applies here, and in addition the secret door between them is usually closed (sector 158), nor can a monster enter sector 157 unless the player guides it there in a convoluted manner.
145 ↔ 190 Major. The imps emerging from the nukage tunnel cannot step onto the walkway (linedef 456), so they can easily be shot from the rocket launcher room without retaliation.
148 ↔ 190 Very minor. A substantial area of each sector is viewable, but whenever a monster pursues a player in one by entering the other, the most direct path toward the player only crosses a small corner of that sector. Additionally, monsters can rarely enter sector 148 from the east because of the locked door (sector 218).
149 ↔ 229 Very minor. Only a small corner at the northern end of each sector is viewable, and there is a locked door between them.
178 ↔ 181 None. Monsters cannot enter either sector.
220 ↔ 236 Very minor. Sector 236 is a damaging floor, which discourages most players from standing guard there. A player in sector 220 could see all of sector 236, but monsters would very rarely enter sector 236 in that case, as it is not the shortest route to the player from any other sector.
220 ↔ 238 The northernmost shotgun guy in sector 238 (Thing 118), if approached from the west, can usually be knocked down before it can take cover or come forward into sector 223. A player very familiar with the maze layout might be able to lure other monsters into ambushes across the same room.


E1M7: Computer Station[edit]

Sectors Effect on gameplay
3 ↔ 68 None. The height of the interposing windowsill (sector 4) makes targeting a humanoid in either area impossible.
13 ↔ 68 None. The above reasoning for 3 ↔ 68 applies to the north-south corridor of sector 13 (along the window), and the remaining area adjoining sector 52 is completely obstructed by the central pillar within sector 0.
13 ↔ 70 Very minor. The lift in its default position is behind a solid wall (sector 67); even so, the player must aim between vertical obstructions at quite a distance.
20 ↔ 134 Negligible. The affected region in each sector is only a few units wide. Not only does the lift in front of the secret area (sector 135) block all sight lines until lowered, but a monster has no good reason to enter sector 134 unless baited into an area full of slime, and that monster could not itself trigger the lift afterward (linedef type 88).
36 ↔ 163 Major. If the player opens the trap, then enters the rocket launcher room from the east without making any noise, they can easily mow down (at least) the first imp with the chaingun.


E1M8: Phobos Anomaly[edit]

Sectors Effect on gameplay
1 ↔ 31 None. Height differences make a line of sight impossible.
26 ↔ 34 None. Sector 34 cannot be entered.
27 ↔ 34 None. See the entry for 26 ↔ 34.
31 ↔ 34 None. See the entry for 26 ↔ 34.
31 ↔ 35 Minimal. Positioning for a sight line is very strict, and only possible once the two barons are dead. Since spectres and demons cannot attack ranged anyway, the only way for this to be an exploit would be with a respawned baron.
31 ↔ 38 Minimal. See the entry for 31 ↔ 35.
34 ↔ 38 None. See the entry for 26 ↔ 34.


E1M9: Military Base[edit]

Sectors Effect on gameplay
0 ↔ 47 None. The floor of the main exit area (sector 15) is 88 units above the floor of the nukage passages, which makes sighting a humanoid opponent impossible.
0 ↔ 48 None; see the above entry for 0 ↔ 47.
10 ↔ 48 None; see the above entry for 0 ↔ 47.
15 ↔ 48 Negligible. Sector 48 is a door which cannot be opened by monsters, so it is normally unoccupied. The player of course must traverse it after raising the exit bridge, but since it is a damaging floor, this is presumably done with all haste.
21 ↔ 49 Negligible. A player could be shot at from one of these sectors while standing in the other only by compounding counterproductive strategies, such as leaving the exit bridge lowered, taking a redundant route over several damaging floors (thereby baiting monsters toward unusual locations), and allowing the imps in sector 47 to attack him at point-blank range.
54 ↔ 88 None. The height of the central courtyard (sector 61) prevents targeting a humanoid opponent in either area.
61 ↔ 83 Minor. The height difference and the narrowness of the passage block all sight lines excepting an oblong region near each end of the staircase. If a monster in sector 83 approaches the player by entering this region, it sooner or later reaches sector 85 and can fire again. The player's protection in sector 83 may last long enough to be noticed (if they are badly wounded, for example, and they can shoot well enough to keep some of the pursuing zombies off the stairs).
61 ↔ 88 88 → 61 actually affects normal play: the imp guarding the yellow key can easily be slain before it finds its way around the barrier. 61 → 88 is subject to the reasoning of 61 ↔ 83 above, although the fence texture and the increased distance make it more difficult to aim up the stairs.
61 ↔ 125 Negligible. Until the blue key trap is triggered, there are two interposing walls (sectors 126 and 130); even so, this only affects a tiny sliver of sector 61, and in all likelihood if the player leaves enough monsters roaming about the level to benefit, the additional attacks suffered elsewhere more than compensate.
63 ↔ 121 None. The height of the lift prevents targeting a humanoid opponent in either location.
64 ↔ 66 None. Monsters cannot enter either sector.
72 ↔ 88 None; see the above entry for 54 ↔ 88.
73 ↔ 88 None; see the above entry for 54 ↔ 88.
77 ↔ 88 None; see the above entry for 54 ↔ 88.
82 ↔ 88 Very minor. The above reasoning for 61 ↔ 88 can be applied to the imp in isolation (although a monster circling a player is willing to sweep out a wider arc at close range), but while the player descends the stairs and dodges the other inhabitants' attacks, during which time the imp itself can also fire, the imp often finds its way around the fence. During a protracted firefight in the yellow key room, a player theoretically benefits from misfires now and again, though they would be almost impossible to identify at game speed, besides which a monster in sector 88 is always on the verge of wandering into sector 83 or sector 89, which are not rejected.
88 ↔ 98 Very minor. The player cannot enter sector 98. Almost all of sector 88 should be visible to the caged imps (they can target a player who stands at least 138 units from the edge of the stairs), but if the player cannot spare the time to kill these imps, they will probably visits sector 88 too briefly to notice the increased safety.


E2M1: Deimos Anomaly[edit]

Sectors Effect on gameplay
14 ↔ 49 Minor. Although most of sector 49 is affected if the player stands in the southern corner of sector 14, an approaching monster will attempt to cut the corner around the blue key area, and thus occupies sector 49 momentarily if at all. Sector 49 is a damaging floor, so the player presumably wants to leave as soon as they have entered.
32 ↔ 34 Very minor. In theory, the imp in the exit room is briefly vulnerable if the player opens the door and then leaps straight back into sector 34. However, any player with such competent footwork could probably also outdraw one imp at short range. Given that both monsters in the exit area are initially between the teleporter and the exit switch, the player probably cannot maneuver into a position where they gain the protection of sector 32 without exposing themselves to more attacks than they hope to avoid.
32 ↔ 35 Very minor; see 32 ↔ 34 above.
38 ↔ 45 Negligible. The line of sight between the two sectors is often blocked by the marble door (sector 44), which cannot be opened by monsters. Because sector 45 is a teleporter, a player can exploit its protection only by racing through the secret passage, then spinning to aim back into the main area before the marble door closes or the target walks under it. A monster can enter sector 45 only by wandering directly away from the player or being baited into the secret passage; the first case requires the player to keep the marble door open until the victim returns (probably while under attack), the second case exposes the player to additional fire in the secret passage, and then of course the monster's first action is to charge the player, thus vacating sector 45. On top of it all, most enemies in this area lack ranged attacks.
79 ↔ 83 Very minor. There is a locked door between the two locations (sector 87). Sector 79 is a damaging floor, and so is not an ideal firing platform for the player; even hopping across to bait the monsters in the secret area is probably more trouble than it is worth. Normally, if the player stands in sector 83, a monster can enter sector 79 only by wandering away from him, which is not its first pathfinding strategy.


E2M2: Containment Area[edit]

Sectors Effect on gameplay
3 ↔ 9 Negligible. Monsters cannot enter sector 9 until the exit bridge is raised, and are unlikely to do so even then, as it requires opening a door while moving away from the player. In theory, a player fleeing pursuing monsters into the exit room is shielded, but only transiently, whereas the exit switch is immediately to hand.
9 ↔ 25 Negligible. Only a miniscule corner of each room is affected, monsters have little or no incentive to enter sector 9 (as with 3 ↔ 9 above), and fireball attacks would nearly always be blocked by interposing corners anyway.
16 ↔ 25 Very minor. Only a narrow slice of each sector is affected, and given the number of monsters in this area, the occasional misfire is unlikely to be noticed at game speed.
17 ↔ 41 Negligible. Only a small corner of each sector is affected, and they are sufficiently far apart that the player probably cannot move between them before any pursuing monster(s) have cut the adjoining corner and entered sector 16 or 43, respectively.
23 ↔ 26 Negligible. Sector 23 is a fast crusher with a starting height of 96, so it is almost always vacant (one way or another).
34 ↔ 157 Negligible. Although a substantial area of each sector is visible, their nearest separation is 2032 units.
40 ↔ 41 Minor. An agile player might be able to exploit the available sight lines by targeting one monster at a time, though said monster can simply close on the player by entering sector 39 or 42, respectively.
40 ↔ 157 Negligible. Only a narrow slice of each sector is visible, and they are too far apart for a hitscan attack.
82 ↔ 208 None. The height of the top step (sector 91) makes targeting a humanoid opponent in either sector impossible.
157 ↔ 244 Very minor. Although a substantial area in the corner of each sector is affected, they are not the corners through which an approaching monster tends to pass.


E2M3: Refinery[edit]

Sectors Effect on gameplay
36 ↔ 96 Very minor. Architecturally, this is a glaring error in the table as the metal portico provides a wide sight line between the two sectors. However, nothing stops a monster from simply walking through the portico to close on the player. It is also difficult for monsters to enter sector 36, as secret #2 cannot be opened from the back side, and the moving platforms hinder their approach from the north.
36 ↔ 98 Very minor; see 36 ↔ 96 above.
44 ↔ 63 Minor. Geometrically the situation is similar to 36 ↔ 98 above. Because there is a door between the room and the hallway, it is also possible to open the door carefully (from the corner, outside sector 47) and get in the first blow against the monster(s) guarding the key.


E2M4: Deimos Lab[edit]

Sectors Effect on gameplay
0 ↔ 128 Very minor. Only the cacodemon has a ranged attack, and its first reaction is to move forward into sector 18. To lure non-flying monsters into sector 128 would be a tedious process at best, since they cannot operate the square lift by themselves.
22 ↔ 39 Negligible. Sector 39 is an extremely narrow firing platform for either a player or a monster. Because sector 22 is a dead end, a monster has no particular reason to stay there anyway.
23 ↔ 35 Negligible. The height of the interposing ledge (sector 39) prevents targeting a humanoid opponent in sector 23. Sector 35 may protect the player from an occasional shot by a flying monster, but it is also a damaging floor.
23 ↔ 39 Incrementally greater than 22 ↔ 39 above, as the dead end has a larger area.
61 ↔ 154 Minor. An atypically large corner of each sector is affected, but nothing prevents a monster from simply advancing into the connecting chamber (sectors 153 and 152 respectively).
100 ↔ 147 Very minor. Monsters cannot enter sector 147. The player cannot enter it either until the large blocking door is opened (sector 102), and even then, many of the nearby monsters are too meaty to kill in the time it takes them to cross sector 100.
105 ↔ 115 Negligible. The crowd approaching from the supercharge area has no ranged attacks, so this would seem to be relevant only for a long strafing-and-turning fight within the slime, which presumably would not be the player's preferred approach.
110 ↔ 115 See 105 ↔ 115 above.
112 ↔ 115 See 105 ↔ 115 above.
134 ↔ 176 Minor. A player standing on the teleporter can benefit from misfires as monsters approach from the slime area or from secret #2. On the other hand, sectors 134 and 138 do not cover the entire room, and it is difficult to dodge fireballs within a 64-unit square. 176 → 134 is an unimportant case, as the player cannot bait a monster into teleporting from the start area without exposing themselves to more attacks than they hope to avoid.
138 ↔ 176 Somewhat less than 134 ↔ 176 above, since monsters approaching the teleporter from the slime area are unlikely to pass through sector 138.
148 ↔ 201 None. Sector 201 is too thin for any actor to stand in.
156 ↔ 165 None. The height of the interposing catwalk (sector 161) prevents targeting a humanoid opponent in either location.
158 ↔ 165 None; see 156 ↔ 165 above.
175 ↔ 182 None. Monsters cannot enter either sector.
199 ↔ 200 Negligible. The player could not bait a monster into entering the first room without exposing themselves to more attacks than they hoped to avoid.


E2M5: Command Center[edit]

Sectors Effect on gameplay
5 ↔ 22 Negligible. No monsters with ranged attacks can enter either area without the player having opened a door for them, and only a narrow slice of each sector is visible.
5 ↔ 28 Even less than 5 ↔ 22 above, since only a miniscule corner of each sector is affected.
16 ↔ 71 None. The height of the interposing window sill (sector 4) makes sighting a humanoid opponent in either sector impossible.
82 ↔ 94 Minor. A player with good footwork theoretically gains some protection as monsters arrive at the west end of sector 94, but only by repeatedly hopping forward to reopen the SR door (sector 98). Enemies approaching a player in sector 94 tend to be vulnerable only for an instant as they cut the corner at the top of the steps (vertex 126).
83 ↔ 94 Less than 82 ↔ 94 above, since the interposing corner now blocks most of the stair sector.
84 ↔ 94 Negligible. The above reasoning for 82 ↔ 94 applies, but only to a tiny corner of each sector.
86 ↔ 105 None. The interposing window sill (sector 125) is 88 units above the floor of the start room, which makes sighting a humanoid opponent impossible.
87 ↔ 90 Minor. Sector 90 is large enough, and its south door narrow enough, to provide some temporary protection as monsters there do not necessarily approach the player directly. The sectors, however, are normally separated by two closed doors, one of which is difficult for monsters to open.
87 ↔ 105 None; see 86 ↔ 105 above.
87 ↔ 128 None; see 86 ↔ 105 above.
94 ↔ 203 Negligible. Although a wide sight line exists, exploiting it is extremely awkward: the sectors are separated by two doors which cannot be opened by monsters and are 1216 units apart.


E2M6: Halls of the Damned[edit]

Sectors Effect on gameplay
6 ↔ 19 Minimal. By the time the imps in the northwest section activate in sector 19, returning to sector 6 would move them out of the area.
11 ↔ 32 Possible, but less likely than 11 ↔ 37.
11 ↔ 34 None; terrain occlusion.
11 ↔ 35 None; terrain occlusion.
11 ↔ 36 None; terrain occlusion.
11 ↔ 37 Possible: Involves fake exit, and possibly a monster could attack from there. However, no monsters are generated around that area.
83 ↔ 107 Very minor; only small window from western darkened maze alcove to main corridor.
83 ↔ 108 Minor; there are only a few ranged enemies.
100 ↔ 139 Very minor; by the time the player can use this, monsters are either alert or can go through the door.
127 ↔ 139 Minor; protects against some ranged attacks.


E2M7: Spawning Vats[edit]

Sectors Effect on gameplay
10 ↔ 26 Very minor; only a small coverage area.
11 ↔ 26 Very minor; only a small coverage area.
19 ↔ 59 Minor; 59 contains exit switch.
19 ↔ 61 Very minor; 61 is dead-end nukage pit.
19 ↔ 62 Very minor; 62 is dead-end nukage pit.
19 ↔ 74 Minor; 74 is dead-end nukage pit, but is in clear view.
19 ↔ 75 Minor; 75 is dead-end nukage pit, but is in clear view.
25 ↔ 59 Medium; 59 contains exit switch, and is likely the place where some monsters would otherwise make the last attack.
43 ↔ 74 Minor; 74 is dead-end nukage pit, but is in clear view.
49 ↔ 50 Minor, but could be exploited. 49 is a nukage pit leading to a secret, and nearby enemies are demons with melee attacks that cannot otherwise approach the player.
80 ↔ 90 None; 90 is inaccessible.
80 ↔ 108 May allow free shots from the northern room to the corridor past the yellow door.
80 ↔ 219 May allow free shots from the northern room to the corridor past the yellow door.
81 ↔ 90 None; 90 is inaccessible.
90 ↔ 137 None; 90 is inaccessible.
108 ↔ 127 Negligible; very small window of opportunity.
108 ↔ 132 May allow sniping past yellow key door.
125 ↔ 157 Minor.
125 ↔ 158 Allows sniping imps in room overlooking blue key courtyard.
125 ↔ 159 Allows sniping imps in room overlooking blue key courtyard.
127 ↔ 219 Allows sniping imps in room overlooking blue key courtyard.
132 ↔ 219 May allow sniping past yellow key door.
150 ↔ 156 Minor, prevents attacks from nearby nukage pit to switch in blue key area.
150 ↔ 157 Minor, prevents imps from room overlooking blue key courtyard from sniping.
150 ↔ 158 Minor, prevents imps from room overlooking blue key courtyard from sniping.
150 ↔ 159 Minor, prevents imps from room overlooking blue key courtyard from sniping.
165 ↔ 192 Unlikely; occluded by terrain.
165 ↔ 193 Unlikely; occluded by terrain.
171 ↔ 195 Unlikely; occluded by terrain.
285 ↔ 304 The demon behind the blue key gate is blind. Can also be exploited to allow safe attacks.


E2M9: Fortress of Mystery[edit]

Sectors Effect on gameplay
0 ↔ 3 None. Neither the player nor any monster can enter sector 3.
1 ↔ 3 None. See the entry for 0 ↔ 3.


E3M2: Slough of Despair[edit]

Sectors Effect on gameplay
0 ↔ 48 Moderate. Sight is possible, but monsters being attacked would likely stray to nearby sectors that are not rejected.
2 ↔ 48 Minimal. The same problem as 0 ↔ 48 but with stricter positioning requirements.
31 ↔ 53 Moderate. A similar condition to 0 ↔ 48.
31 ↔ 55 Moderate. See the entry for 31 ↔ 53.


E3M3: Pandemonium[edit]

Sectors Effect on gameplay
1 ↔ 61
2 ↔ 3
5 ↔ 19
5 ↔ 21
19 ↔ 24
38 ↔ 40
39 ↔ 107
39 ↔ 108
39 ↔ 109
39 ↔ 110
39 ↔ 115
39 ↔ 121
39 ↔ 122
59 ↔ 72
59 ↔ 73
67 ↔ 168
107 ↔ 111
107 ↔ 112
108 ↔ 112
109 ↔ 112
116 ↔ 147
116 ↔ 171
133 ↔ 189
139 ↔ 147
147 ↔ 186
163 ↔ 166


E3M4: House of Pain[edit]

Sectors Effect on gameplay
100 ↔ 115 None. Sector 115 cannot be entered.


E3M5: Unholy Cathedral[edit]

Sectors Effect on gameplay
155 ↔ 158 None. A line of sight is not possible due to height differences.
155 ↔ 160 None. See the entry for 155 ↔ 158.


E3M6: Mt. Erebus[edit]

Sectors Effect on gameplay
16 ↔ 87
16 ↔ 88
16 ↔ 93
41 ↔ 86
41 ↔ 121
47 ↔ 115
60 ↔ 73
83 ↔ 121
84 ↔ 121


E3M7: Limbo[edit]

Sectors Effect on gameplay
0 ↔ 5 Moderate. A clear sight line is available, but in order to use this the player would have to stand in lava, losing health. The monster might not stay in sector 5 either.
0 ↔ 6 Moderate. See 0 ↔ 5.
0 ↔ 10 Minor. Monsters are unlikely to enter either sector.
1 ↔ 4 Moderate. Very similar to 0 ↔ 5.
14 ↔ 54 Major. The cacodemon in 14 can be killed without retaliation.
14 ↔ 67 Moderate. Like 14 ↔ 54, but 67 is a hurt floor, so 54 would be used instead.
14 ↔ 74 Major. See 14 ↔ 54.
14 ↔ 75 Major. See 14 ↔ 54.
17 ↔ 54 Major. See 14 ↔ 54.
17 ↔ 57 Moderate. See 14 ↔ 67.
17 ↔ 74 Major. See 14 ↔ 54.
17 ↔ 75 Major. See 14 ↔ 54.
27 ↔ 39 Minor. Sight is possible, but it is a very long distance shot and monsters are not likely to stay still.
29 ↔ 49 Minor. A long range shot and neither sector is likely to contain any monsters.
29 ↔ 55 Minor. See 29 ↔ 49.
32 ↔ 39 Moderate. In either case monsters will simply move closer and then engage, but the player can score some free shots.
37 ↔ 39 Moderate. See 32 ↔ 39.
38 ↔ 39 Moderate. See 32 ↔ 39.
86 ↔ 105 Minor. A sight line is almost impossible.
86 ↔ 106 Minor. Sector 106 is a hurt floor so there is little incentive for the player to be in it, and monsters are unlikely to enter it.
87 ↔ 106 Minor. See 86 ↔ 106.
95 ↔ 142 Minor. It is very unlikely that a monster will ever enter this area.
124 ↔ 133 Minor. It is very unlikely that a monster will ever enter either sector.
124 ↔ 140 Minor. See 124 ↔ 133.
124 ↔ 141 Minor. See 124 ↔ 133.
124 ↔ 142 Minor. See 124 ↔ 133.
124 ↔ 143 Minor. See 124 ↔ 133.
124 ↔ 148 Minor. See 124 ↔ 133.
135 ↔ 152 Minor. It is very unlikely that any monster will ever enter either.
136 ↔ 152 Minor. See 135 ↔ 152.
141 ↔ 150 Minor. See 95 ↔ 142.
148 ↔ 164 Minor. See 124 ↔ 133.
151 ↔ 164 Minor. See 124 ↔ 133.


E3M9: Warrens[edit]

Sectors Effect on gameplay
29 ↔ 33
39 ↔ 69


E4M1: Hell Beneath[edit]

Sectors Effect on gameplay
29 ↔ 42 Major. This prevents the imps and spectres in the red key room trap from seeing the player until they makes a noise. Probably intentional. Because they will teleport out once they hear the player or get hit, it is not very exploitable.
44 ↔ 62 Moderate. Sight is possible, but once the player has access to sector 62 they can immediately exit.
44 ↔ 63 Minor. Only monsters can enter sector 63, and only once the blue key door has been opened. In addition, a monster would not likely stay in 63 for long, and there is nothing holding them there. Player sight from 44 → 63 is probably not possible anyway.
48 ↔ 63 Minor. Similar to 44 ↔ 63, except a clear player sight line from 48 → 63 is easily possible.


E4M2: Perfect Hatred[edit]

Sectors Effect on gameplay
4 ↔ 36 Minimal. A cacodemon in the extreme southwest corner of sector 4 might be able to sight to 36, but would not remain there for long.
4 ↔ 83 Minimal. Height differences make 83 → 4 impossible; 4 → 83 would let the player kill any cacodemons in sector 4 with relative ease if they were still alive at that point.
19 ↔ 36 Low. Precise positioning that monsters would not keep is required for a line of sight.
32 ↔ 97 None. Height differences make this sight impossible.
33 ↔ 98 None. Height differences make this sight impossible.
33 ↔ 116 None. See the entry for 33 ↔ 98.
77 ↔ 113 None. Height differences make this sight impossible.


E4M3: Sever the Wicked[edit]

Sectors Effect on gameplay
6 ↔ 52 None. Height differences make this sight impossible.
7 ↔ 52 None. See the entry for 6 ↔ 52.
23 ↔ 52 None. See the entry for 6 ↔ 52.
35 ↔ 96 None. Sector 35 cannot be entered.
50 ↔ 52 Low. There is very little room to work with, but a line of sight could potentially be made.
111 ↔ 120 Medium. While monsters would try to close the gap, and closer sectors between the two are not rejected, a clear line of sight is possible in either direction. To keep the door open, the player would need to be in 120.


E4M4: Unruly Evil[edit]

Sectors Effect on gameplay
44 ↔ 45 None. Players and monsters cannot enter sector 44.


E4M5: They Will Repent[edit]

Sectors Effect on gameplay
15 ↔ 73
47 ↔ 73
50 ↔ 73
73 ↔ 137
73 ↔ 142
110 ↔ 151
121 ↔ 124


E4M6: Against Thee Wickedly[edit]

Sectors Effect on gameplay
0 ↔ 32 Minor. Very position dependent, and only works on cacodemons in sector 0 due to height differences.
0 ↔ 106 Moderate. Similar to 0 ↔ 32, but an easy sight line is possible. Probably exploitable on cacodemons.
35 ↔ 42 None. Height differences make sight impossible.
42 ↔ 56 None. See 35 ↔ 42.
42 ↔ 60 None. See 35 ↔ 42.
42 ↔ 66 Minor. One could potentially shoot cacodemons in 42 from 66, but positioning is very strict.
101 ↔ 102 Major. Clear sight is possible, and monsters could be killed before they move to a sector that is not rejected. Unlikely to affect anything more than the death of a single shotgun guy.
105 ↔ 130 Moderate. The player would need to be in 130 to keep the door open, and its unlikely that many targets would stray into 105 and stay there.
111 ↔ 130 Moderate. Like 105 ↔ 130, but the two sectors are closer. Sight is easier, and monsters would be more likely to stay in 111.
116 ↔ 139 None. Height differences make sight impossible.
116 ↔ 140 None. See 116 ↔ 139.
128 ↔ 139 None. Sectors 16 and 17 are in the way.
128 ↔ 140 None. See 128 ↔ 139.
139 ↔ 183 None. Sector 183 cannot be entered.
139 ↔ 198 Minimal. Too position dependent.
140 ↔ 183 None. See 139 ↔ 183.
167 ↔ 205 Moderate. Sight is possible, but in either direction monsters would quickly move to non-rejected sectors.
168 ↔ 205 Moderate. See 167 ↔ 205.


E4M8: Unto the Cruel[edit]

Sectors Effect on gameplay
0 ↔ 42
17 ↔ 42
18 ↔ 42
23 ↔ 64
23 ↔ 93
23 ↔ 184
34 ↔ 43
34 ↔ 183
34 ↔ 184
35 ↔ 95
49 ↔ 95
57 ↔ 64
58 ↔ 64
59 ↔ 64
60 ↔ 64
61 ↔ 64
67 ↔ 71
68 ↔ 71
68 ↔ 73
69 ↔ 71
69 ↔ 73
75 ↔ 95
87 ↔ 95
91 ↔ 95
126 ↔ 201
126 ↔ 202
127 ↔ 201
127 ↔ 202
135 ↔ 170
135 ↔ 204
144 ↔ 155
201 ↔ 216
202 ↔ 216


E4M9: Fear[edit]

Sectors Effect on gameplay
5 ↔ 24
5 ↔ 45
9 ↔ 24
10 ↔ 24
15 ↔ 24
24 ↔ 73
24 ↔ 74
24 ↔ 75
24 ↔ 76
24 ↔ 124
24 ↔ 125
24 ↔ 159
24 ↔ 184
24 ↔ 187
24 ↔ 192
24 ↔ 201
24 ↔ 202
24 ↔ 204
24 ↔ 226
24 ↔ 235
53 ↔ 82
53 ↔ 123
171 ↔ 199
184 ↔ 199
187 ↔ 199