Colour for Movement

16th July 2009

Single Player First Person Shooter Maps and Mods for Half-Life 1, 2 and Episodes 1, 2 and 3

Allow me to introduce three seemingly unrelated points and then try to bring them together.

Apparently that’s what clever writers do, so I thought I’d try it.

I once remember reading that snakes can only “see” you when you are moving. Of course, I could simply connect to the Internet and check my facts but I prefer to think it’s true. This way it doesn’t make me feel too much of a fool when I freeze on seeing a small snake in the mountains, hoping it won’t notice me!

One aspect of game design that greatly interests me is enemy movement and behaviour. Nowadays, this is known as A. I. (Artificial Intelligence) but I prefer to think that there is more to interesting enemies than just making them more human-like.

Single Player First Person Shooter Maps and Mods for Half-Life 1, 2 and Episodes 1, 2 and 3

I was chatting with CubeDude89 a while ago and he showed me an image he had created (seen on the left). I told him that it looked great and thought nothing of it.

That is until now….

(Time to bring them together….Excited? I am. Be still my beating heart!)

99 percent of the time an enemy sees you when playing an SP FPS game he attacks you. Bioshock developers made a big fuss about how cool their enemies were because they didn’t attack you on sight. Shock! Horror! Blah! Star Trek Elite Force had already done it with the Borg, but it does raise the point that there needs to be something more than complete attack or complete indifference to players by the enemy.

Not only are there plenty of possibilities between those two points, there are also lots of other possibilities.

I would love somebody to build a mod where the overall visual effect was grey, or to put it another way almost complete desaturated. Perhaps on a planet where the light from its sun and some effect of the atmosphere makes everything look grey. That is until it moves. It then bursts into colour. Through millions of years of evolution predators and prey have developed movement and other techniques that take advantage of this phenomenon.

Let me make sure you understand what I am suggesting. When the player or enemy stops moving they fade into the background. Since everything is grey they almost become invisible.

The faster they move the brighter the colours are.

At first glance this concept might be better for MP games, and it could certainly make for an interesting experiment, but as regular readers will know I don’t give a flying headcrab for MP games and try to turn everything I think of into something related to SP gaming. 🙂

Since most computer controlled enemies remain more or less still (as they would if this were a real environment) it would force the player to draw them into the open by moving and becoming a target. Of course it could work nicely for some daylight stealth gameplay.

When the player or enemy is not moving they don’t become completely invisible but simply blend very closely with the background.

Now, imagine a non-humanoid alien on this world. It can only see you when you are moving. The moment you stop you effectively disappear from view. Of course, the moment that happens it starts to search for you by moving about. Can you hold your nerve and keep perfectly still? Can you resist the temptation to attack when it is right next to you? Why should you? Because this particular alien only needs to hit you once and you are dead. If he bumps into you when searching for you are more or less assured of being killed. So unless you can guarantee killing it very swiftly it’s better to remain more or less motionless.

Clearly plenty of beta testing would need to be done with something like this because players just aren’t used to this type of gameplay and it’s quite unnatural.

One scene that comes to mind is in the first Predator movie where Arnold Schwarzenegger is covered in mud and the Predator can’t seem him because it uses heat to sense its prey and the mud has masked his heat signature. Whilst this is not exactly the same, the concept is similar.

Some Details

I mentioned earlier that there were many possibilities between attack and indifference. Let’s explore some with direct regard to the colour/movement idea. Let’s assume that the brightness is directly related to speed of movement. If something moves slow enough then it stays on the edge of visibility.

When certain enemies see very bright colours they almost ignore them. Why? Because this particular alien is quite cumbersome and knows that it is unlikely to catch any fast moving prey.

Next, it also ignores a stop start movement pattern. Why? Because this type of prey tends to be very small and it has evolved to ignore this signal because it’s simply not worth the effort.

Of course, I should point out that the player doesn’t know this when they start the game or mod. This would be one of the aspects of this particular game; finding out which strategies work best for which alien.

Perhaps the game or mod is set on a world the Combine have invaded, in much the same way they did with Earth. The player is transported to this world while infiltrating a Combine base. Anyway, I digress.

Let’s not forget that this works both ways. The player can only easily see enemies when they are moving quickly too. This means simply relying on looking around is not enough. Perhaps it needs to use the environment to their advantage (this would need to be built into the design document from the very beginning).

Developers can create enemies that once they sense the player they adapt their movement accordingly. Instead of immediately attack they player they perhaps remain still until the player is within a certain distance.

Another possibility is that the enemy only moves when the player does. It also never moves directly towards them but it a zigzag pattern. At the same time it still moves very slowly after it has stopped, so that the player can never be entirely sure where it will be.

With planning and skilful implementation this could turn into a kind of chess game where the player has to carefully adjust their movement under changing circumstances.

Take it one step further and imagine an open area where the player encounters two types of enemies within this area and has to decide which enemy is more dangerous at any given point.

I’d also like to see some enemies that actually try to keep as far away from the player as possible. This could be for a number of reasons. One, to try and draw the player into a weaker position and then attack or two because it is part of a pack and has been assigned this role to distract you. It still tries to attack you from longer distances but has very little effect.

Which brings me onto my next point; consistency; I’d like to see less consistency with regard to enemies. When I am fighting the Combine I’d like to see and hear some fear. Why not have the last fighter in a group look around and realize they are alone and retreat, especially now that Gordon Freeman’s reputation is known throughout the Combine ranks?

There must be plenty of other option similar to the above example. What I am saying is that I don’t just want smarter A.I., but I want something deeper too.

Isaac Asimov

For those that haven’t heard of Isaac Asimov, visit the link but suffice to say he is considered one of the greatest science fiction writers ever. Why do I mention this? Well, even though I forget most of the stuff I have read I clearly remember reading one of his short stories where the human heroes encounter an alien that can only see them from one side of its body. A bit like those fish that lie flat in the ocean. One of their eyes has moved around to the other side of their body.

This alien only ever attacks with the sun behind it or from the west or something like that. The point I am trying to make is that must be plenty of variation in enemy movement and behaviour, especially with regard to aliens. Here is one last example. Larry Niven wrote a book called Footfall about an alien invasion of Earth. In it the aliens, who were Elephant-like creatures, assumed that once they placed one their considerable feet on a human’s chest the fight was over.

This caused a little confusion at first because the humans didn’t understand their behaviour. Of course since the book was written by a human about humans they eventually use it to their advantage. (It’s a good book and I highly recommend it).

So, there you have it. Colour For Movement.

Would it work?


  1. CrowbarSka

    This was actually used in the recently-released multiplayer mod Neo-Tokyo. One of the character classes has motion-sensor goggles.

    However, that is human players fighting other human players and the kind of combat you suggested could end up being very different. I honestly love the idea of being stalked by some big, powerful creature and having to remain absolutely still even when it is right next to me. It reminds me of that famous T-Rex scene in Jurassic Park: absolutely terrifying!

    Are you familiar with Metroid Prime on the Nintendo GameCube? You play as a human character but your ship has crashed on an alien world, and you get to observe (and fight) many different kinds of creatures with varying behaviours. I really like that idea of discovering new species of animals and plants, some hostile and some not. There could even be some kind of ecological system where certain aliens prey on others. Maybe if you protect some of them they can act to your advantage (open up new routes or something).

    1. I love the idea of killing one enemy but not others and the way that could work. Especially if you could make it look like one enemy killed another – kinda set them against each other.

  2. Kyouryuu

    “Bioshock developers made a big fuss about how cool their enemies were because they didn’t attack you on sight. Shock! Horror!” […] “Let me make sure you understand what I am suggesting. When the player or enemy stops moving they fade into the background. ”

    Maybe you should complete BioShock before panning it. Someone didn’t find the Chameleon Tonic…

    1. I wasn’t panning the game just the fact that the developers made a big fuss about the enemies not attacking you.

  3. SolidFake

    some interesting concepts there, it was ever one of my favourite moments when I have hidden in a closet in Metal Gear Solid 2 and the enemies out there are searching for me, slowly opening one closet after the other. I really didn’t know what todo, should I go out and fight? Or running away? Or hope that the alarm counter goes down before they come to my closet.

    btw: Snakes can’t hear, because they have no ears. They feel the vibrations from the earth, that’s why they don’t “hear” you when you stand still and why they are afraid when you stomp on the ground. But they still can smell and see you 😉

  4. andi

    This could work. This could work very well. The AI would have to be planned…. well, let’s say that you could fit a flow chart for HL2’s combine AI onto an A4 sheet. I postulate that the level of detail required to do the suggested (without rethinking the whole approach to AI) would take up atleast an A2 sheet. A challenge worthy of the gods themselves. Beta testing, even alpha testing would take forever. Would the result be worth it, however? Yes, I say. Infact, I would dearly love to get cracking on this right now, but (again, postulation), it would take a good few years.

    I really wish to see this style of gameplay realised; it could definately be considered a “step forward” for games.

  5. Isaac Asimov is a real science and science fiction writer par excellence.
    To the get spelling of his name wrong is nearly akin to blasphemy!
    Please PP, correct and then remove this comment. Thanks.
    For the post – I’ve read it but need to understand it before making a comment, if any.

    1. Fixed, strange I made the mistake twice.

      1. Thank you PP. You mention Larry Niven. A writer of heroic imagination and, together with a few others including Asimov and A. C. Clarke, somewhat prophetic. An example being “A Gift from Earth” being very relevant to today’s obsession with human spare parts. His earlier works were enormous in scope and variety. ‘the Legacy of Heorot” is a must read for HL gamers.
        A link for those who do not know:
        Off topic? Not actually because readings of these works give a greater understanding of the question(s) posed in the this post as well as feeding the imaginations of game writers and players.
        Indeed, this post is deeper than it might appear and needs careful thought and response.

  6. Zanpa

    Very interesting, but waaay too hard to create.
    That’s why it doesn’t already exist (or in a much simpler form).

  7. Wesp5

    The Source engine FPS/RPG hybrid Vampire: The Masquerade – Bloodlines already uses a kind of similar feature for the player. Some clans have a discipline (spell) that makes them practically invisible but at early levels only when they are not moving. It’s nice to see yourself blend into the background the moment you stand still.

  8. reaper47

    Nice. This is the kind of enemy idea that seems obvious at first (ever since Jurassic Park the “it can’t see you if you stand still” idea has become rather popular), yet with the exception of some RPG-style invisibility-gizmo, this has hardly, if ever, been done in an FPS.

    Would love to see an enemy like that for Episode 3, for example. It would be a nice counter part to the be-quiet-that-thing-HEARS-you tentacle from HL1.

    1. Yes, for Episode Three it might be cool because of some of it being set against a white background.

  9. Freyband

    Reminds me of multiple enemies throughout the games I’ve played over the past years.
    You mention an enemy running away when alone. That reminds me of the raiders from Fallout 3. If hurt enough (or too many teammates die) some will run away. The trying to keep distance from the player (vaguely) reminds of a boss fight from Dead Rising where the boss uses a sniper and runs when the player gets close (or sometimes when he can’t get a shot at you). The enemy only moving when you do I remember from the Third (I think) Legend of Zelda game. He also could only be killed via a slash/shot/? to the back so you’d have to trick him to getting him to turn his back to kill him. As for the attacking when you move a certain speed it reminds me one of the creatures from the first Half-Life games (I’ve only found called as tentacles so far, not too suiting for these giant green freaks). The thing was blind and only reacted to loud noises. So you move slow it’s oblivious to your presence, yet the mappers of Half-life made it so there were crate you had to smash to get on w/ the map. You smash it the things attack where you made the noise as well as the general area nearby, but if you were to do something like throw a grenade the things would move to where the explosion was and attack that area instead). You could chose to do something like run (never turned out well for me :P) or sneak by (turned out bad often but it worked better then running).
    I think seeing elements like this in HL2 mods (or continuations) would be amazing.

  10. My draft comment was too long and V. boring! A brief version:
    As a game player I have no idea how these things are or can be done.
    To a very minor degree some games have done something similar. Eg in Unreal 2 when the ship lands for repairs some enemy engage you while others try to break intio the ship.
    Overall I think PP makes some interesting and insightful points.
    Except for one: I don’t think I would enjoy a game where the player and/or the enemy merged into the background if still or slow moving. We would all be inching around to avoid being seen. A very small map would take an awful long time to play.
    Might work as a very very brief transition between chapters.
    Meanwhile; Snakes vision varies from non-existant to very keen. Common to all is a sharp sense of smell using their tongues. I’m off for a jolly good licking.

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