Special Design Considerations for Vehicle Simulations

Some design issues are particular to vehicle simulations and are described in the following sections.

Creating the Sense of Speed

In a flight simulation, there's little need for a sense of speed because simply flying fast is rarely the point. Most players either are trying to fly accurately and aerobatically or are engaging in aerial combat. Although speed is an important factor in the game, conveying that sense to the player isn't critical to the experience.

In driving simulations, however, the sense of speed is all-important. Here are some ways to create it:

• Give the player a speedometer . This is the most obvious way to inform a player of his speed, but it creates a purely logical awareness, not a visceral one. It might also help to give him a tachometer so he can see that the engine is near its maximum potential.

• Vary the driving surface. Don't present a smooth ribbon of black, but make the road a series of continuously changing dark grays. (Look back at Figure 13.3, NASCAR 4 , to see this done well.) The rate at which these move toward the car will help to create the feeling of speed. Don't just use a set of random dots, though, or at high speed they will just look like a static, flickering surface. It's better to implement them as a series of narrow strips parallel to the road's edges. Also, on roads (as opposed to racetracks), be sure to implement the dotted white line down the center. The sight of the lines flicking by gives a continuous visual cue to the speed, as well as a good way to tell when the vehicle is speeding up or slowing down.

• Include roadside objects. A continuous fence, guardrail, or strip of grass doesn't do much to give the player a feeling of motion. Make sure there are lots of trees, road signs, and bridges. Anything that is vertical beside the road, or that passes over or under the car, will help to create the impression .

• Use sounds. The sound of the engine is the most obvious auditory cue, but there's also road noise (the sound the tires make on the pavement), wind noise, and tires squealing as they round corners. Another excellent cue is a Doppler shift as the car passes, or is passed by, some noise-making object.

G-Forces

The driver of any vehicle feels a variety of forces affecting her body: acceleration, deceleration, and centrifugal force. She can feel these forces as pressure driving her body in one direction or another, usually into the seat or against the belts holding her in. The forces give a lot of valuable feedback about the behavior of the vehicle. Unfortunately, in a simulator, we can't provide any of those feelings to the player, so we have to substitute other indicators. With driving simulators, it doesn't matter that much because automobiles seldom generate significant G-forces, and the player has plenty of other visual cues, as described in the previous section.

Military aircraft can generate powerful G-forces, but because the player spends most of her time looking at the sky, there's nothing to indicate them. The engines of modern fighter planes are powerful enough to tear the plane apart if it is mishandled, and if you're doing a realistic simulation, you might want to include this deadly little detail. If so, you should include a G-force meter showing the amount of stress being applied to the plane (and pilot). Most aircraft are designed to sustain strong downward G-forces, but not upward ones. In addition, pilots undergoing strong downward G-forces can black out momentarily as all the blood drains out of their heads. They can also suffer an experience called redout if they encounter a strong upward G-force, as too much blood flows into their heads. Many games simulate these conditions by fading the screen to black or to red, which, in addition to preventing the player from seeing anything, gives a clear indication that something is wrong.

Designing Opponents

The easiest way to design a variety of opponents in a vehicle simulation is simply to vary the performance characteristics of their vehicles. One plane climbs slightly faster than another; one can turn more sharply. The player will experience different challenges in dealing with each one based on their design parameters. However, this kind of variety is static and, after the player has figured it out, is easily beaten. As soon as he discovers that a Supermarine Spitfire can consistently outrun a Messerschmitt BF 109 in level flight, it offers an obvious strategy for Spitfire pilots: "boom and zoom" ( hitting and running away).

To create further variety in the behavior of individual opponents, the AI for those opponents should be designed around getting perfect performance from the vehicle and then creating variations from perfection . For example, it's possible to create a "perfect" AI driver in a racing simulation. He always follows the most efficient line around the track, he always shifts gears at precisely the correct moment, and he knows the ideal speed at which to take each corner without spinning out. If such a driver has a better car than the player's, he will be unbeatable. The trick, then, is to modify the AI driver's judgment so that it isn't perfect ”so that he doesn't always shift at exactly the right time or follow the most efficient line. It is the combination of factors, both vehicle characteristics and variable driver skill, that provides the variety among opponents in vehicle simulators.

As you study the business of flying or driving, you will discover other tricks to incorporate into the AI: drafting behind other cars , for example, and diving out of the sun to surprise the enemy in a dogfight.

Intellectual Property Rights

As a general rule, you can model and simulate military equipment without obtaining permission from their manufacturers. Because such machines are not sold to the general public, nor are generally exploited in any other way, their appearance is in the public domain. Automobiles are another story, however. If you are going to simulate an existing car and use its real name and logo, you must have a license from the manufacturer. The manufacturer might not be willing to let you show the car crumpled and burning by the side of the road, either. This accounts for the large number of vehicle simulations in which the cars can flip over in an accident but never get damaged ”they flip back upright a second or two later, as in Beetle Adventure Racing . Or, you can do as Interstate '76 did and model cars that look rather like existing vehicles and have similar names , but don't actually use the manufacturer's indicia.

Vehicle Simulation Worksheet

When beginning the design of a vehicle simulation, consider the following questions:

1. What vehicle are we going to simulate? Is it an existing car, plane, boat, tank, and so on, or is it a fantasy-vehicle?

2. If it is an existing vehicle, are we aiming for the purist player who knows all its technical specifications, or for the casual player who simply wants to enjoy using it? How detailed is the physics model going to be?

3. How will the game handle damage to the vehicle? Can it be visually shown to be damaged? (Licenses for real vehicles sometimes forbid this.) Will damage be treated globally, like hit-points, or locally for individual parts of the machine?

4. What are the competition modes and victory conditions in the game? If this is a military vehicle, what sort of missions are available for it? If it is a civilian one, what kinds of things can it do besides simply racing (if anything)?

5. What settings are available for the vehicle to travel through? Even a flight simulator needs ground to look at below.

6. What camera views are appropriate for this vehicle? If it is a military vehicle, are there special camera views that assist in fighting? Can the player record and even edit instant replays so as to re-live and show off his triumphs?

7. How will we map the many controls of a plane or even a car onto the input devices available to the player? What aspects of the vehicle's controls will need to be simplified? Which can afford to have simple on-off buttons and which require analog controls?

8. If a vehicle is capable of steering in a different direction from that in which it shoots, how can the player control both at once conveniently?

9. What navigational facilities is the player going to need to know where he is (radar screen, overlay map, separate map mode that pauses the game, and so on)?

10. What artificial intelligence is needed to create decent opponents in the game's competitive modes? What sorts of things will the artificial opponents need to manage? Will they be smart enough to take advantage of superior speed, acceleration, cornering ability, braking ability?

11. Do we want to create a sense of speed for the player? If so, how will we create it? (Remember, you can use both visual and audible cues.)