[Vanilla Level Editing] Lesson 12: Populating Your Doom World

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BONUSES

Once the major items are in place, the Spiritual Armor and Health Potion bonuses can be sprinkled around as you feel necessary — usually either in secret locations, as an incentive to enter and collect the secret credit, or as a quick boost before the next major combat. Generally, you can set the same bonuses on all skill levels — they may be all that will keep the player alive in the upper settings! Indeed, you may already have placed most of these items when you laid out your medical supplies.

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ADDITIONAL DECORATIONS

Finally, any additional decorations that you feel are necessary for atmosphere can be positioned around the WAD. You may add these purely for effect or to serve some other purpose — as warnings, for example. Pools of blood beneath crushers are common in many WADs, as are corpses outside particularly hazardous areas. (Or just scattered around to make players nervous!) Mostly, what you use will be a matter of personal taste. Use whatever you feel fits into the general design of your WAD but, as always, don’t overdo it. Avoid too much decoration in areas with large numbers of monsters, or you will run the risk of sprite overload.

At this stage of the design, try to avoid adding any items classed as obstacles, unless they are well away from the main action. Otherwise you risk upsetting the balance of play which you have worked so hard to produce. If you particularly want decorative elements to contribute to the hazards of a level, add them early, rather than late in the design, so that they are in place while you are testing the layout of their areas.

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EXTRAS

At this stage, your WAD should be just about ready. Try playing it from beginning to end without any cheat codes at all. Ask yourself how it works as a whole. Is there enough variety? Are things distributed correctly? Are there any unnecessary holes in the action? Refine the way it plays by adjusting any of the elements already in place. You might also want to add a few new items to break up any unevenness in the way the WAD plays.

To add a little unpredictability to a WAD, you might consider introducing a few wandering monsters. Placed where they will be awakened early, either by seeing or hearing the player, but in an area where they will take a long time to appear, such monsters can be made to pop up unexpectedly in a slightly different place each time. (Ways of achieving this are discussed after the next WAD Sortie.)

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FINAL REVIEW STAGE

When you are completely happy with the way your WAD is playing, pass it to someone else to play, and ask for their comments. If you can, watch the way they play it — you’ll get a better feel for whether your traps and signals are working as you expected them to. If you can’t be there to watch their game, ask them to record a demo of it. Watch this through a few times, making notes of what aspects of the WAD are working as you intended and which ones still need improvement.

Don’t keep asking the same play-testers to look at your levels after each minor change, though — they’ll most likely just get bored and not give it a full workout. Only pass it on again when you think you have made all the significant improvements you can think of and feel you have things as good as they can be.

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WAD SORTIE 27: CHECKING THE FLOW

By way of preparation to the real populating of the WAD, this Sortie will look at the steps involved in checking the flow of play through your WAD. It starts by considering the placing of the keys for those keyed doors.

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THE INTENDED FLOW

It is time that I revealed to you my intended control of flow through the WAD you have been building. The keyed doors are already in place; I ought to tell you now where I planned to place the keys.

Currently, players can explore west from the starting room, by passing through the platform room, whence the whole of the western half of the map is accessible. Alternatively, a player may start by venturing east into the maze. The remaining areas of the map are locked away behind the blue-keyed door off the southeast passageway. One of the two acessible areas will need to hold a blue key-card, therefore.

In reality, two keys are needed before a player can progress much further. The blue key-card only grants access to the outdoor crescent area — all further doors are locked with red or yellow cards. I have used this arrangement to force players to tackle both the maze and the western area of the map before proceeding anywhere else.

The yellow key will need to be acquired before players can locate the exit from this level. The planned positioning of the keys is as follows:

• Blue key: Located just outside the north window of the platform room. This key will be accessible only after the player has successfully negotiated both the bottom corridor and the arena.
  
• Red key: Hidden in the maze. By locating the key to the “back entrance” of the maze in the maze itself, it becomes impossible for a player to use the back stairs until the maze has already been visited. Measures will be taken to ensure that the player does not leave the maze without having first located the red key — read on!
  
• Yellow key: Located in the donut room, the yellow key requires that room’s puzzles to be solved before it can be acquired. Before that, though, the two other keys will need to be obtained, to gain access to the donut room itself.
  

Once all three keys have been found, the player is free to leave the level.

It is worth considering the rationale behind the placing of these keys in a little more detail.

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THE BLUE KEY

The blue key will be placed where a player will quickly see it — reaching it will prove to be the problem here. Offering an early sight of a key in this way provides players with an incentive to explore the area further. This key needs to be positioned where it will be visible from within the platform room — provided the northern window is open, that is! Call the locating of this key a reward, then, for approaching the upper level of the platform.

In my WAD (D2WAD27.WAD), the key has been placed on a pedestal so that it is conspicuous through the window of the platform room. It can be reached from the Imp ledge — if the player makes it that far, of course!

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THE RED KEY

The red key is also to act as a lure—this time in the more usual way, to entice players over a trigger line. This trigger will not perform the expected trick of opening a monster-pen — it will, in fact, be used to open the teleport that acts as an exit from the maze. To achieve this, a slight modification to the current WAD is required. The teleport sector needs to have its ceiling lowered to its floor. This change ensures that the player cannot leave the maze without taking both the key and locating the teleport.

Maybe the trigger should open a monster-pen as well, to mask the sound of the teleport opening…

Once the teleport in the maze has been found, it provides the area with an easy exit, making the trips on the back stairs that open the one-way staircase redundant. They can be used, though, to add another little twist here. Consider what would happen if we were to add another trigger action to the self-raising stairs, this time to close the teleport sector again.

Remember that these stairs cannot be reached without the red key. Anyone entering the maze by this route will, therefore, already know about the teleport, and, in all likelihood, the trap of the oneway stairs. After arriving back in the maze by this route, a player will in all probability head straight for the teleport. Unfortunately, it won’t be there any more!

A player’s next logical move will be to head back to where the red key was located to try to reopen the teleport by retriggering the appropriate line. That approach needs to be foiled too. The line that opens the teleport sector as the red key-card is taken needs to be a once-only walk-through trigger. This will force the marble stairs to be used as the exit on this second visit to the maze — when the player eventually thinks of trying them!

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THE YELLOW KEY

The yellow key is already in place as the prize for solving the puzzles in the donut room. No further consideration needs to be given to this item’s contribution to the flow of the WAD.

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TRYING OUT THE FLOW

You may like to place these various keys now, with suitable modifications to the appropriate areas of your own WAD.

When you’ve done this, see how it affects the flow of the WAD as a whole. Try running through from start to finish, visiting just those locations that are necessary to attain the exit.

Note that two areas do not need to be visited: the southern courtyard and the back stairs to the maze. The southern courtyard contains several secret areas. Their credits will remain uncollected until the player visits them. The player is not penalized at all for not using the back entrance to the maze, however. The figure shows how this has been remedied by the addition of some further secret areas, with a cache of goodies off the corridor at the top of the self-raising stairs.



Also conspicuously undeveloped are the maze itself and the large open arena (which also still has temporary switching arrangements in place for the causeway across the pond).

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ARENA DEVELOPMENT

The following figure shows how the arena might be developed further, as in my D2WAD27A.WAD. The development here concentrates around the watchtower, north of the pond. A lift has been added to permit access to this watchtower, activated from a nearby switch. From the tower, an additional step provides access to the arena’s northern balcony. The top of the watchtower has two switches. The more conspicuous of these will raise the ceiling trap in the green stone corridor, should that have been tripped. The second, hidden round the back of the first, will be the proper switch for raising the causeway from the pond — it will replace the temporary switch that was installed for testing purposes.



Allowing players onto the watchtower and the balcony compromises the impediment to progress caused by the pond — there is nothing to prevent players from simply leaping down from here. To rectify this, the southern and eastern edges of the watchtower and the south side of the balcony need to be set as impassable.

To explain the blockage, my WAD uses the MIDGRATE texture on both of the main textures of these lines. This creates railings to stop the player from jumping down to the eastern section of the arena. Additional sectors have also been placed around the watchtower to provide pillars to terminate these railings and to bring the ceiling down around them so that they look right from both sides.

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UNDERSTANDING AND CONTROLLING THE ENEMY

The strategy for testing the deployment of monsters in the WAD was presented earlier. To be able to place the monsters properly in the first instance, though, it is necessary to understand something of the standard modes of behavior of DOOM’s monsters and the ways in which these can be controlled through the layout of a WAD.

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STANDARD MONSTER BEHAVIOR

As you will know from playing DOOM, the basic behavior of monsters is to stand at their posts asleep until something awakens them. Once awake, they will stand still no longer and will start to track the player. If a player is in sight, monsters who are capable of it will sooner or later start firing.

If within striking range, most monsters will bite players or rake them with their claws. Former Humans prefer to back off a bit, though, to carry on using their weapons.

There are three things that will awaken a “sleeping” monster:

• Catching sight of a player
  
• Hearing a noise made by a player
  
• Being hit by fire
  

Once awakened, monsters do not normally go back to sleep — although they will when a player resumes a saved game—a common form of cheating!

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USING AMBUSH MONSTERS

To prevent monsters from waking when they hear a sound, you can use the monster’s ambush flag. Setting this flag will cause them to awaken when they catch sight of a player or are damaged by gunfire — either from a player or from one of their fellows.

Many editors and documents refer to the ambush flag as the "deaf" flag, which paints an inaccurate picture of its function. Ambush monsters will "hear" gunshots like normal monsters, but instead of waking up, they will instead "lie in wait" for the player to enter their field of view. A complication is that an ambush monster's "field of view" upon enter the lying-in-wait state encompasses 360 degrees; it is impossible to sneak up on an ambush monster if they have heard you and are lying in wait.

Sometimes you will not want to set this option, for you will want to draw monsters from immediately adjacent areas, to make combat come to a player no matter how the level is tackled.

Usually, though, you will not want to draw monsters from too far away. It would be undesirable, to say the least, to have all of the enemies in a WAD zero-in on the player’s first pistol shot! To learn how to control the way sounds draw monsters into the fray, you need to know something of DOOM’s principles of sound propagation.

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SOUND PROPAGATION

Once again, the way monsters hear noises differs from the way in which a player hears them. Monsters will only hear sounds made by a player’s weapons discharging. (This includes the chainsaw and the fist!) Monsters will not hear players grunting as they walk into walls or jump off high platforms. They are also immune to the sounds of doors and lifts operating, as well as of their fellows firing or crying in pain.

Sounds from a player’s weapons propagate through the DOOM world in a standard way. First, a sound will immediately fill the player’s current sector, waking every non-ambush-flagged monster within it. It then travels across every line that has the two-sided flag set and where the arrangement of ceilings and floors leaves an air gap into an adjacent sector. Sound will not pass into sectors that are completely obstructed, such as a closed door or a sealed-off lift, for instance, or through any lines which have their two-sided flag unchecked.

You should be able to see that, left to its own devices, this propagation of sound could quickly have most of a WAD’s monsters awake and on the trail of the player. Fortunately, DOOM provides a mechanism to prevent sound from propagating wildly throughout an entire WAD and waking your monsters prematurely: a line’s Blocks Sound flag. Lines with this flag set impede the progress of sound from one sector to another.

This line does not operate in the same way as the Blocks Monsters or Impassable flag, however. It will not always prevent sound from crossing the line. First, it cannot stop sound spreading through an entire sector. Lines with the Blocks Sound flag set that are not between sectors will be entirely ineffectual. This flag is only examined by the engine when it determines whether or not sound can be propagated into an adjacent sector.

Further, sound is only stopped at the second Blocks Sound line it encounters. This means that sound will always pass into the sectors adjacent to the player’s sector, provided there is a suitable air gap.

These lines are intended to allow sound to fade away through a level, rather than completely isolating sectors sonically from their neighbors. They also have no effect on the sound that the player hears while playing the game. That is handled completely differently.

GZDB happens to have a Sound Propagation Mode available from an icon on the sidebar, which allows you to visually see how far sound will propagate from any particular place in a level. Of course, this mode operates on the initial state of the level, and does not account for changes such as doors opening and closing, which can cause sound to propagate into areas you may not want.

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TRACKING TALENTS

A further inequality between monsters and players is the monsters’ ability always to sense the direction in which players lie. They use this sense to home in on players and to track them through the WAD. Fortunately (for the player), this ability is a straightforward homing talent — it often leads monsters into dead ends.

You may wish to impede monsters in their player-tracking and contain them in particular areas by setting the Blocks Monsters flags of some lines of your WAD. Remember, though, that such lines block the movement of all monsters, including the flying ones. If you only want to stop ground-based monsters from tracking through certain areas, consider using raised or sunken floors instead.

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TELEPORT TRAPS

The sound-propagation rules can also be used to awaken monsters that otherwise would never be awakened. This can be combined with monsters’ player-tracking capabilities to create monster caches that deliver monsters into the game, either at irregular intervals to the keep the player on guard, or in a rush to overwhelm the player at inopportune moments.

This technique is used in many of id Software’s own levels. Take a look at the west edge of DOOM 2’s MAP16 for an example of the latter type of cache.



In this area, a thin open sector acts as a sound conduit into a room that is otherwise isolated from the rest of the WAD. The conduit carries the player’s sounds into the isolated room, to awaken the horde of monsters waiting there. In the starting condition, the monsters are no threat to the player, because, apart from the thin conduit, the room is sealed.

A player who is lured onto the pedestal to the south by the sight of the goodies there is in for a surprise, though. The edges of the sector are tagged to open the thin sector in the corner of the monster-filled room. This arrangement causes a teleport on the side of the monsters’ room to become accessible once a player has stepped into the sector. Once this has occurred, their ability to track the player will draw the monsters en masse over the teleporter lines to materialize in the area with the player.

Sound conduits such as this are not always necessary to carry sound into a monster cache, though. The next WAD Sortie shows another way to achieve the same effect by utilizing the sound propagation rules in a different way.

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SUMMARY OF MONSTER-PLACEMENT CONSIDERATIONS

Here is a summary of the main points to remember when laying out monsters in a WAD.

• Use monsters’ facing-angle option to watch (or not) the entrances to areas, so that the monsters are awakened as the player passes particular points in each area.
  
• Set a monster’s ambush option if you want a monster to wait until it sees a player before waking.
  
• Use a suitable array of lines with the Blocks Sound flag set to prevent all nondeaf monsters in your open combat areas from waking at the first sound the player makes.
  
• Use level changes or lines with the Blocks Monsters flag set to contain monsters within certain areas and prevent them from tracking the player in an undesirable way.
  
• Consider how the rules of sound propagation and monsters’ player-tracking abilities can work to provide sudden monster releases or a steady stream of monsters into areas that players think have been cleared.
  

The next WAD Sortie gives some practical examples of these ideas in use.

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WAD SORTIE 28: DEPLOYING THE ENEMY FORCES

This Sortie starts with a new development of the WAD: a monster cache. Figure 12.8 shows the form and location of this.

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ADDING THE MONSTER CACHE

Notice where the new room is located, in the open space left by the curve of the western green stone corridor, beyond your first lift. To add this area, you should begin by drawing the main rectangle of the new room using GSTONE1 as the wall texture. Instead you should add the new lines to an existing sector. I’ve used the short corner sector of the corridor.

To add the new lines to this sector, choose Linedefs Mode, and click-drag a box over the new sector you just made. Once all the linedefs are selected, right-click on one to edit them all at once. Now, manually index the "Sector Index" field to be the same sector number as the existing one.



There are, of course, no sector settings to change for the new area—it shares those of its disjunct part in the corridor. If you change one area’s settings here, you will change the other’s: this is all one sector, remember.

Because it is all one, any sound reaching the corridor section of this sector will immediately propagate through to its disjunct part. Sound from any shots the player fires in the green stone corridor — or indeed out in the arena beyond, if the door is open — will therefore penetrate through to the new area and will awaken any nondeaf monster that you choose to place there.

Let us make use of our new monster cache by adding a route out of the new room for whatever has been awakened. Draw and make additional sectors off the four corners of the new room as shown previously in the figure. Make the lines across the entrances of these into teleporters, delivering monsters to various locations around the WAD. Make some of these deliver to points nearby, while others carry monsters further away. Use your knowledge of the way monsters in this room will follow the movements of the player to decide where each teleport will deliver.

As an additional twist, let us allow the player to vary the way in which this monster cache delivers its load. Start by making the heights of the ceilings of the two teleport sectors that deliver furthest from the corridor the same as their floors. Then tag each of these sectors to the switch line in the unused (southern) alcove located in the corridor near the bottom of the lift. Put the special attribute of 103 (S1 Door Open Stay) on this switch. Now, until this switch is thrown, the new room will deliver monsters closer to, rather than farther from, the corridor. It may be quite a while before a player figures out what the switch achieves — and whether it is useful or not.

Finally, populate the new room with some monsters and place a few columns in the room to stop the monsters from moving too freely along the walls. This should slow down their arrival at the teleports. If you want to be able to get into the room and take a look at it, turn one of the lines of the corridor into an active teleport line that will take you there. The room should have three Imps, four green columns, and a teleport destination in it to permit player access. Three of the room’s own teleport delivery points can be seen in nearby corridor sections.

Notice, incidentally, how this addition has turned the corridor ceiling trap into something of a double-edged sword. Is it worth cutting off the line of retreat before entering the arena in order to prevent the propagation of sound to the new room? Probably. The last thing a player will need here is an additional attack from behind — as will occur if that ceiling is left up! This has provided players with an unexpected gain from an apparent trap. I wonder how many times they will need to play before they learn this though?

When you’ve saved the WAD (D2WAD28.WAD) and seen how it works — you should hear the monsters wake up when you fire a shot in the bottom corridor — reload it into the editor and remove the temporary teleport line from the bottom corridor. Leave the teleport landing in the new room, though — tagged instead to all of the lines surrounding the yellow key at the center of the donut.

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DEPLOYING THE REST

The final section of this Sortie considers an initial trial distribution of monsters throughout the WAD. It is meant to suggest the kind of monster layout that I had in mind when I designed the geography of the WAD. Add monsters at Hurt Me Plenty, as suggested forthwith, first. Resist temptations to vary the forces until you’ve tried it out like this.

HEXAGON ROOM

Leave the starting room as it is, with just a suit of armor on the platform. There will be plenty to fight later on.

SOUTHEAST PASSAGEWAY

Place a couple of Former Humans here. (The player still only has a pistol, remember.) Position one of them so that he will see the player heading for the suit of armor.

MARBLE STAIRS

Players heading up the marble stairs are going to need a better weapon to face what’s up there. You’d better have a Former Human Sergeant guarding the bottom of the stairs to supply a shotgun!

SECRET ROOM AT TOP OF STAIRS

This room should have a good mix of nasty beasties in it: some Imps, a Demon or two, and some Spectres, perhaps. Place at least one Spectre, with its deaf-guard option set, hiding in the depths of the room. (We don’t want the player to empty the room completely from the corridor, do we?) Put a chaingun in the depths of the room, too—the player will need it later.

MAZE

The maze isn’t finished yet, so it is not a good place to populate right now. You may want to set some sound-blocking lines across the entrance to it, though, so that when the maze is used, it won’t empty too quickly as a result of the fight that is likely to occur in the corridor outside. Return now to the western part of the map.

PLATFORM ROOM

Remember that players can enter the platform room before venturing anywhere else, and may still be armed with only a pistol. Place some Former Humans around the floor level, along with a Sergeant or two, either on the platform or around the room. There should be some Former Humans on the platform, too, to encourage the player to go up there.

OUTSIDE THE PLATFORM ROOM’S NORTHERN WINDOW

There should already be some Imps waiting for the platform room’s northern window to be opened. Set their Level 1 flags to bring them into the game.

SOUTHERN COURTYARD AREAS

The southern courtyard and its associated areas should still be populated from the test games. Change their skill-level flags to bring these Imps into the game, too, along with the sniper in his den. Put an Imp (or two) in the secret room off the southeast corner of the courtyard, with some barrels about the place. Leave the crushers as the only hazard in the southern corridor, at least for now.

Place another chaingun in the sniper’s den, in case the player comes this way rather than going up the marble stairs. Put some barrels here, too.

SOUTHWEST STAIRS

Try a couple of Lost Souls in the secret room off the southwest stairs, and maybe a Spectre or a Demon. Decide whether you want them to see the player as the door is tripped, or whether you’d rather have them wait until the player returns—or shoots to open the doors at the end of the corridor. Set one of them deaf anyway. Leave the rest of the corridor empty.

STRING OF SHOT-ACTIVATED DOORS BEYOND THE BLOOD POOL

Place an Imp or two behind a couple of the doors beyond the blood pool. Don’t let them get too close to the lift, though—you don’t want to risk the monster cache being triggered too soon.

BOTTOM CORRIDOR

Leave the bottom corridor empty. Any shots fired here spring the monster cache, remember.

ARENA

The arena is planned as the main combat area. Start it out with a couple of Hell Knights: one on the northwestern platform, guarding the lift, and another on the eastern platform. Put some Imps and a Former Human or two in the basin and on the steps by the pond. You could put some Imps on the balcony and maybe on the watchtower, but you will need some monster-blocking lines to prevent them from coming down on the lift.

Finish this first attempt off with a deaf Cacodemon hiding behind the watchtower to catch players once they’ve found and crossed the platform.

Don’t forget to set up a sound block between the arena and the platform room; otherwise you’ll have these arena monsters awake long before the player makes it down there—which will spoil the layout. Don’t forget that you will need two lines between the platform room and the arena in order to block the sound. You’ll know whether you put them in the right place or not as soon as you open fire in the platform room.

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GOING ON

When you’ve placed all of these, save the WAD (D2WAD28A.WAD) and see how the areas work. There are no extra ammunition or health stocks out yet, of course, so you’ll need some cheat keys to make it to the end.

After you’ve looked at the way this WAD operates — pay particular attention to the way the arena plays and to the way the monster cache delivers up its occupants — I’ll leave it to you to decide what more it needs and where. From now on, in fact, this WAD is entirely in your hands. Feel free to add whatever you think it lacks. Good luck — and have fun!

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EXIT: MOPPING UP AND MOVING ON

In this lesson, you learned more about the behavior of DOOM’s creatures, as well as the rules for sound propagation through a WAD. You were presented with a strategy for the population of your WADs. If you have been completing the Sorties, your own WAD should be nearly finished by now. The next lesson considers some additional changes you might want to incorporate into your WAD for enhanced multiplayer use. It also looks at ways to improve its playing speed and shows you how you might produce WADs that contain more than one level.