Sample Design Doc :

An excerpt from the Design Document. This section dealt with our core gameplay – sneaking I made the following to illustrate what I pictured our stealth system should be, before discussing it with our AI programmer.

 

 

Stealth

 

Did you know 4 elements make up how the environment affects the player?

In turn, based on the player character’s interaction with the game environment, he becomes less, or more, noticeable to other NPCs, whether they are friendly, neutral or hostile. In the case of Hostile NPCs, the player will want to avoid them whenever possible, and so stealth becomes a major focus of gameplay, as we strive to create a system both realistic and versatile, yet remaining fun and intuitive.

 

Briefly, in order of importance:

 

Light: Light will make the player more apparent, and thus, give him away to guards that are within visible range. Likewise, areas of shadow make the player less visible, and areas of intense darkness allow the player to become almost invisible

 

Movement: the faster the player moves, the more likely he is to be spotted. This is combined with lights, so that moving fast or for a long period of time will you more visible, even when hiding in shadow.

 

Disguise: disguise plays a part in stealth, as it decreases the power and range of a Guard’s ability to recognise you and attack you. When a disguise is working it is a benefit to the main character, increasing his ‘stealthiness’. When the player is recognised, the disguise has a negative affect and making him more detectable to enemies.

 

Sound: the amount of noise the player makes by moving over surfaces and interacting with the environment. Sound does not directly affect the visibility of the player to guards, but it does leave clues to where the player has been, and if loud enough, can quickly draw a lot of unwanted attention.

 

So, the following is a basic outline for setting up a stealth system that will work to make sure each action of the player is represented by a change in his stealth profile [I’m going to use this term to reflect all the aspects of the environment’s effect on the player’s ability to remain unnoticed].

 

 

Example Stealth Profile

All things factored the player is:

 


            1                      2                      3                      4                      5                      6

       Invisible                                                                                                      Lit up like Xmas

 

 

The two main factors in stealth are Light and Movement, as these, continually changing as the player progresses through a level, will be the primary reasons why, and how, enemy NPCs will detect the player.

 

LIGHT

The lighting system will use the in-built character lighting model of the engine, which lightens and darkens the character model according to the level’s lighting. Several areas on the model will measure the amount of light falling on the character, and the sum of the light will be taken for the overall light value. This will measure areas of shadow (0 percent light) as well as the intensity of the light the character is exposed to. For example, a player may be semi-concealed from a powerful searchlight, but the areas exposed are very brightly lit and thus have a high stealth profile. In contrast the player may be standing fully exposed under a 20watt lightbulb, but the actual light is so dim, the stealth profile is quite low.

 

The system outlined above means that the player will not only need to register how much he is concealed, but also how bright the light he is concealed from is. In the example given it may be a better choice for him, to walk slowly under the lightbulb than to move quickly past the searchlight, shadows aside, as the AMOUNT of light determines his stealthiness.

 

 

Example of Location Based Light Detection

 

 

 

                                                     Head: 30/33%

Total Light Reading: 35%
 
 

 

 


                                                         Torso: 5/33%

 

 

 


                                                      Legs:  0/33%

 

 


In the example above, only the player’s head is exposed to light, however, the light that he is exposed to is very bright, and so his visibility is not that low (a little over a 1/3). If he were completely exposed to alight that merely registered as 2% on all the sensor zones, he would still be considered quite well hidden.

 

The light reading works closely with the movement rating…

 

<Queue movement>

 

Movement

Is simply calculated based on the input of the player. Each speed of movement available to the player is rated, so for example:

 

            Action                              Movement Rating

Standing still:

0%

Walking while crouched:

15%

Walking

30%

Jogging while crouched

50%

Jogging

75%

Running

100%

 

Therefore, it is always better to walk then run or jog, and always better to move crouched rather than standing. However, when combined with the issue of light, the decisions the player has to make become more complicated; it may very well be better to run through a dimly-lit area and take your chances, than try to creep under a 10,000watt floodlight.

 

The above example is just a selection of the player’s basic moves. Naturally, all animations will have related movement values, so that anything the player does, from quickly climbing up some vines, to creeping with his back to a wall, to sliding down a cable, will affect his Stealth Profile dynamically.

 

Movement also affects the amount of sound the player makes on the type of surface he is moving over. This is discussed in more detail below in the sound section. While sound will certainly attract the unwanted attention of NPCs, like Disguise, it does not directly affect the Stealth Profile.

 

Together, the player’s Light rating and Movement Rating provide a dynamic basis for how well avoiding being noticed, his Stealth Profile. This is the major part of the system covered.

 

 

 

Additional Factors

 

Disguise  

 

Disguise is a gameplay system that affects the player’s stealth, as well as letting him access certain areas and talk to certain NPCs.

 

The player will be able to obtain disguises from various NPC types (Scientist, Engineer, and Executive) and the impact on stealth will work by changing the reaction distance and speed for NPCs that encounter the player when wearing a disguise.

 

For example, an NPC who would become hostile to the player at 30 meters and curious at 70, might now become hostile at 5, curious at 30, and ignore the player beyond 70 meters. Here’s an example:

 

 


Player undisguised:

 

Range:              5m        15m      25m      35m      45m      55m      65m      75m

                        |           |           |           |           |           |           |           |

 


 Enemy     Alerted (becomes hostile)            Curious (investigates player)            Player

 

 

 


Player disguised:

 

Range:              5m        15m      25m      35m      45m      55m      65m      75m

                        |           |           |           |           |           |           |           |

 


 Enemy     Alerted          Curious                                     ignored                         Player

 

 

So, in terms of stealth, disguise waylays the range, and desire, of NPC’s to investigate or attack him on sight.

 

Disguise Drawbacks:

When the player is wearing a disguise, and his real identity is discovered, whether by getting too close to an NPC guard, drawing a weapon, attacking someone, or having the disguise’ previous owner discovered, the disguise will no longer be considered effective. The player will need to find another suitable ‘donor’ if he wishes to continue without being attacked automatically. Thus, the effect of the disguise is reversed when the player is found out. Instead of affording him a longer reaction time and wider berth around hostile NPCs he will now discover that NPs will attack him as soon as he comes within their visual range, regardless. The effectiveness of his disguise will need to be shown on-screen as a bar or icon, or on the player model himself (perhaps turning transparent as the effectiveness gets reduced.)

 

 

Sound

Sound will work on a global system, where every material, and certain character actions, will have a sound rating assigned by the designers. These sounds will be picked up by NPCs and some interactive objects, when they fall within their detection radii. This ‘Sound Scale’ works in the background, and does not actually represent the sound the player will hear. Rather, the Sound Rating is a value given to a material that will be sent out to any NPC’s within hearing distance, when something comes in contact with it, that tells that NPC how load a sound he heard. This allows us to configure NPCs to react differently to different sound events.

 

 

The Global Sound Scale

               

0

1

2

3

4

5

Inaudible

Barely audible

Soft

Noticeable

Loud

Very loud

 

The system I propose is this: Each surface material, be it horizontal, vertical or sloped, will have a sound rating assigned. This rating reflects the sound made when the character moves over it at a crawl. This means that for each speed of movement, the noise generated will go up one point. For example:

 

Material Type: Wood

Sound Rating: 1

 

Sound Rating Results:

 

Walking: 1

Jogging: 2

Running/jumping: 3

 

Or

 

Material Type: Metal

Sound Rating: 3

 

Sound Rating Results:

 

Walking: 3

Jogging: 4

Running/jumping: 5

 

 

Walking on a surface with a sound rating of 0, the player could be mere inches from an enemy without them noticing anything. On the other end of the scale, if the player were running on metal then all NPC’s that were within range of the sound would be on him like a tonne of bricks

 

 

 

 

 

Non-movement

The sound rating also provides the level of noise a surface will make when something is thrown at, or on it. So when the player picks up a jar of syrup, and throws it onto a carpeted floor, the sound that it makes will be of the rating specified by the designer. This means that, for simplicity’s sake, the sound rating a coin makes when thrown onto a wooden floor would be the same as that of a plaster garden gnome. This is not highly realistic, but it makes things a great deal easier when calculating a global sound scale.

 

Not just materials…

The Sound Scale doesn’t just apply to materials though. Certain events and animations will have Sound Ratings applied. For instance, each weapon will have a volume attributed to it so that NPCs can be made aware of when a gun is fired or a grenade detonated, even if they are not within visible range. Also, certain designer-placed triggers may cause sound events, like when the player opens a squeaky door, uses a certain item, or struggles with an NPC.

 

The Sound Rating is merely a way to make sure the player is punished or rewarded based on his interactions with noisy elements of the game.