A GAMES DESIGN BLOG

Continuity Level Design is a school of Level Design predominantly used by Single Player games. 

Recent examples include Portal, Mirrors Edge and Call of Duty 4. 

Now it’s worth pointing out that the phrase “Continuity Level Design” is something I’ve just made up (well at least as far as I’m aware).

I’ve chosen the name based on the similarity in concept to Continuity Editing in Cinema.

There are a few rules that characterize Continuity Level Design:

1. The Player Always Knows What They Are Doing
2. The Player Always Knows Where They Are Going
3. Everything Happens In-Front of the Player

If the above list looks like it’s making the Player the centre of the universe then that’s because it is. Everything about this school of Level Design is based around their being a single perspective on events.

What Am I Doing?

The most important part of Continuity Level Design is to ensure the Player always knows what it is they are doing in your level. 

This isn’t about long-term objectives like “Rescue the Princess” or “Defeat the Terrorists”. 

It’s about the question “How do I get from Where I am to Where I want to be?”. 

Any time a Player stops and thinks “What am I supposed to be doing?” is a failure on the part of the Level Designer. 

An Example:

The Player is stuck in a building with only one way out. This exit is guarded by some enemies who cannot be killed by the players weapons.

To escape the building the player must shoot a specific spot on a wall which will kill the two guards allowing the Player to continue.

The spot on the wall is completely indistinguishable from the rest of the wall. 

The Enemies guarding the way out appear to be regular enemies that the Player has bested in combat a hundred times before. 

Thinking they can just kill the enemies they engage them in combat and are swiftly killed.

This violates a key principle:

• Never contradict the Players understanding of the games mechanics!

Every time the player interacts with something they are building an internal model of how the game works. When that model is contradicted so blatantly it causes frustration and confusion. 

Unkillable enemies are viable mechanics in a video game. However they should never appear the same as an enemy that can be killed.

At this point the player may begin to backtrack around the building thinking they’ve taken a wrong turn or missed something elsewhere.

They’re now having to consciously think about what they are doing and as they start to discover that there is no other way out and they haven’t missed something they will become more and more frustrated and angry. 

The Player is stuck in a building with only one way out. This exit is guarded by some enemies who cannot be killed by the players weapons. 

Above the guards is a wooden platform supporting some concrete blocks. In the middle of the platform is a Gas Canister. 

The Player knows that Shooting a Gas Canister will cause an explosion. 

While the Gas Canister is too far from the Guards to kill them the player also knows that Wooden Objects can be broken. 

Shooting the Gas Canister the Platform breaks apart and the Concrete blocks fall on the Guards and kill them allowing the Player to escape.

As cliche as the example may seem this makes up the majority of Half Life 2′s game play. 

However what is important here is that the player has used their internal model of the games mechanics to solve a problem. The Solution may have been in plain sight but it is up to the player to establish the relationship between the elements and solve the problem. They will adjust the model to include this new information on how to kill this kind of enemy and similar encounters will appear much easier in future. 

Establish a Visual Language

A Visual Language is what Level Designers use to communicate with the Player. The Level Designer should really be telling the Player how to complete their Level.

It is not a competition between the Player and the Level Designer to see who wins.

My favorite example of a Visual Language is Portal.

Every element of a level is introduced one at a time in Portal and how they work doesn’t change after their introduction.

When the Player arrives in a new level they understand the relationships between all of the objects with the exception of whichever new concept is being introduced.

Additionally Portal makes a point of explicitly declaring the relationship between elements within the level itself. In the screenshot above the relationship between the buttons and the door is declared by the trails leading from the buttons to the exit.

The question of “What am I doing?” does not generate game play. What generates the game play is the question “How do I do it?

Where am I Going? 

The question “Where am I going?” seems to go hand-in-hand with “What am I doing?”. 

However this question is much more related to a levels “Flow” and exists mostly at a sub-concious level for the Player. 

Portal makes a point to always tell you as soon as they can where you are going.

In the majority of the challenge rooms you are shown the exit right from the elevator.

As soon as you have arrived you know where you are going to. The trick is figuring out how to get there. 

This keeps the player oriented in the world. Ensuring they have a point of reference straight away.

The Zelda series is very good at making sure you know where to go next while keeping the “How” a mystery to be solved.

If the exit of a dungeon room isn’t obvious from the entrance then you are often treated to a camera cut that shows you where it is and enough of the level to establish your bearings relative to it. 

However not all games want to use a camera cut to show you the world preferring to feed you directions like bread-crumbs.

A Lot of the techniques used to show the player where to go can be borrowed from Photography or Cinema and have been studied in far greater depth than I can hope to go into here.

Composition

While a modern video game is a 3D world the rules of Composition as established by Photography are still very helpful to a Level Designer.

It is important to determine where the Player will look while playing your Level. 

At a high level this is broadly defined by geometry and the actual layout of the level itself.

Everytime the player turns a corner the Level Designer knows where they will be facing and can use this to ensure that important elements fall into their field of view.

A good test is to take a screenshot as soon as you’ve rounded a corner or opened a door and then examine the screenshot out of context. Ask somebody else if they can tell from the screenshot alone where they should be going.

At these points the Player is making a decision about where to go next and the composition of the scene at that point has a huge affect on where the player decides to go.

Contrast

Photographers have been using contrast to lead and focus the viewers attention in pictures for decades. 

Mirrors Edge used this for it’s “Runner Vision” and arguably used it as something of a crutch at times.

Without Runner Vision; and especially at speed, this appears to be a dead end.

However if we turn Runner Vision on…

Lighting

Lighting has additional benefits over tonal or colour contrast.

Well-lit areas are of tactical advantage to a species that has typically poor nightvision and under-developed senses of smell and hearing.

Because of these primal instincts we naturally favour areas of light over the dark and associate them with safety.

The exception to this is the Thief series which turns the concept on it’s head and establishes the light as dangerous and to be avoided.

Left 4 Dead uses Light very well as an aid to navigation:

The bright light in the kitchen draws our eye and focuses our attention towards it.

Even subtle changes in lighting will draw our attention.

When lighting a level it’s important to ensure that the lighting is reinforcing the gameplay as well as making it look good.

If you don’t want the player to go somewhere then shroud it in darkness.

Leading Lines

Lines are used in photography to direct attention around the picture.

Straight diaganol lines tend to have the most power in this respect as they don’t occur often in nature.

The power of lines is increased when there are multiple parallel or converging lines as these will reinforce each other.

The most dominant lines in a level are ussually edges of geometry and the points where the wall meets the floor or ceiling.

Granted in this shot there is only one direction to go: Up. However everything in the shot is reinforcing the up-ness.

The horizontal red block on the left wall is pointing us towards the staircase.

The stairs and the bannister are then pulling our attention up and towards the vertical pillars.

The Two vertical pillars here are drawing attention from their base (the floor) upwards. If the lines are “Rooted” like this then your attention will travel along them in only one direction.

Ambiguous Lines

An example from Mirrors Edge where Lines are actually causing confusion for the player is below:

Immedietly after opening a door we are presented with a choice: Left or Right?

Unfortunately here we are given no clues at all where to go. The dominant lines aren’t grounded and are telling us that both choices are as valid as each other.

I’ve played this level alot (It’s the first one after training) and I still turn left before I turn right.

Now this could be intentional. One of the things to remember about the rules of Continuity Level Design is that they are made to be broken.

Knowing how to lead the player through a level effectively also means you also know how to confuse them on purpose.

Movement

Evolution has granted us an excellent ability to spot the tiniest of movements with almost no effort at all. 

Spiders enjoy using this to scare the crap out of us.

To demonstrate just how good your eyes are at spotting movement have a look at this screenshot of the game “Lost In The Static” by Silver Spaceship. 

Just static right?

Wrong. Download and run the game and you will be able to see the difference a little movement makes.

Here is a YouTube video from GDC of the game in action.

Movement screams out to us even in darkness. Again this is a survival trait we’ve evolved over millions of years and has served us pretty well. It’s also why camouflage works best when neither the viewer or the target are moving.

Using Movement

It’s quite hard to identify where to go in this shot. There are a few tell-tale signs but only one of them really stands out when the game is running.

The spinning C sign not only moves but is shiny so it’s surface is changing as it spins in the sun.

The Spinning object in Mirrors Edge can only ever draw attention to the area it occupies.

However should a Jet fly over the buildings our attention would be immediately drawn along it’s path.

So there are two very simple rules here:

1. Localised movement draws attention to it’s origin.
2. Movement along a path draws attention along that path.

Scripting Movement

This shot from Half Life 2 – Episode 2 demonstrates how a series of moving elements timed well can draw the players attention to an important event in the level.

As you approach this point the path narrows which keeps you facing the desired direction.

To draw your attention to the roof of the building a flock of birds take off and fly up the screen taking your attention with them. Then the Hunter comes into shot on the roof of the building foreshadowing the next section of game play.

All of the elements in this part of the level are leading up to the reveal of the Hunter for the first time.

If something is moving that isn’t aiding the game play then it probably shouldn’t be moving at all.

The Third Rule

The third rule of Continuity Level Design is one that is broken quite frequently.

“Everything Happens In-Front of the Player”

Continuity Editing has a rule that if a character or element is off-camera then it doesn’t move.

This is to ensure that the viewers internal model of the scene stays up to date and in-sync with the action on the screen. 

One exception though is that objects can move around so long as they maintain their momentum.

It is for exactly the same reason that Rule Three exists in Continuity Level Design.

The Players Situational Awareness is based on the current momentum or behaviour of all the objects they know about.

They are assuming that the immediate future is going to be very similar to the present.

In the first level of Mirrors Edge you crawl through an air-vent and drop into a corridor.

The shape of the Air Vent and the direction you face when you drop out of it were specifically designed to ensure that the Player is aware of the enemies waiting for them.

Now the player is aware of these enemies they can add them to their internal model of the world and make predictions about their behaviour.

In the same level after a cut-scene the player is positioned so the very first thing they see are the four new enemies.

The enemies will wait for a couple of seconds before engaging allowing the player time to react and evaluate the situation.

 In the case of Mirrors Edge the Police will always chase you so you can safely categorize them as being “behind you” even though you can’t see them.

Inattentive Blindness

Humans only have a limited amount of attention they can use at once (sometimes referred to as Psychic Energy) and this limits how much data you can consciously or subconsciously process.

You’ve probably seen videos like the one below before but I like this version.

Now I don’t know about you but I’ve seen about a half dozen videos showing this principle at work and I still got caught out at the very end of this one.

Because Attention is a finite resource you need to make sure that when something important happens that the player can process it.

Even if something is happening in-front of the Player there is no guarantee that they have actually noticed it.

You can use all of the same techniques used to tell the Player where to go to ensure their attention is focused on important events.

Altogether Now

To demonstrate all of the above techniques I’ve chosen a short (probably 2 minutes) section of game play from Half Life 2: Episode 2.

Here we see the use of Light and Lines to draw our attention to the left of the scene.

The fences allow us to see part of the world where we will eventually go but indicate to us that we will have to go around them somehow.

Looking left towards the light we can see that we can’t go this way as another fence blocks our path.

However we can make out something blocked by wooden boards and further attention is drawn to it by the Green signs.

In order to get this far we had to break Wooden Boards just like those with the Gravity Gun so we already know that they can be broken.

This has established this part of the world as being important in our internal model.

Turning around we see more light and can clearly tell that this is the way out.

We are also shown a Black Headcrab which is far enough away that we have plenty of time to prepare for it’s attack.

Headcrab dispatched we reach the bottom of the ramp and discover the way out blocked by wooden boards.

These don’t look like the boards we were able to break earlier but if in doubt a few experimental zaps from the gravity gun establish these as the Unbreakable kind.

The Diagonal lines of the Mine Cart tracks draw attention back up the ramp.

Here the lighting and lines are all working to draw our attention to those breakable boards we spotted earlier.

By now we know the solution to the problem as whatever is being held back by those boards is no doubt going to smash it’s way through the Unbreakable Boards.

Breakable boards broken (and getting a tiny bit run-over) and the Mine Cart breaks open the exit and we can progress again.

Again you can see how the lighting and lines are all focusing attention to the point of impact. Add on the motion of the Mine Cart itself and it’s almost impossible for us to look anywhere else allowing us to admire the results of our work.

Parting Words

I started writing this blog post a week ago with the intention of getting some of the things I’ve learnt over the years out into the world for others to learn from.

As such this essentially forms my disclaimer: I don’t pretend to be an expert on everything in here and to cover all the topics in-depth would require a huge amount of time and space. There are good odds I’ve gotten something wrong somewhere or misunderstood or misapplied a concept. If that’s true then I would hope somebody is kind enough to help and explain it better. 

Continuity Level Design is just one part of Level Design as a whole. There is alot more to Level Design than what is in here and I hope to cover more topics at some point in the future.

In the meantime if you want more Steve Gaynor has written a quality post on Combat Encounters in FPS games Here.

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