Ultimate Game Design : Building game worlds

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FIGURE 6-3 Amplitude-modulated sine attack C H A P T E R 6 Here’s an example of modulating the frequency to change the attack pattern: // Alter sine wave attack for enemyactor by modulating frequency function moveEnemy() { enemyactor.moveLeft(); // Modulate sine wave frequency by another sine wave var x = enemyactor.getX%360; enemyactor.setY(100 * sin(x * (2*sin(x)+3) ) + 240); } Figure 6-4 shows the modified attack pattern with the frequency shifted or modulated. FIGURE 6-4 Frequency-modulated sine attack 143 Scripting Scripting Action Events
Building Game Worlds 144 U L T I M A T E G A M E D E S I G N USING TRIGGERS As we’ve seen, some behaviors are handled with scripts built in JavaScript/JScript, Python, Visual Basic, or another proprietary language. Increasingly, however, to complement simple script systems, complex trigger systems are used. A trigger is simply a switch that can cause an event, or series of events, to occur when tripped. This is sometimes called event handling. Building up and using complex trigger systems has a couple of practical advantages. First, value and parameter editors to control trigger properties can be built into Windows-based editors (GUI-based editors) quite easily. Second, designers and artists rarely have more than basic programming abilities (if any), so the property-editing nature and workflow of setting up trigger behavior is much easier for the nonprogrammer. The most powerful world-editing systems combine trigger functionality with line-item scripting (like the shooter behaviors using a sine wave). Triggers are usually placed in a scene and represented by icons in a 3-D scene within an editor. They are completely invisible to the player. Triggers can be used in a number of interesting ways to build up game behaviors. In most world-editing software, trigger properties can be set up to include several types of associated information. These include � True and false modes (to set the logical state or condition of the trigger) � Value fields (to enter radius, distance, strength, and offset information) � Text fields (to print a message to the screen for a player, or for testing purposes) � File pointers (to point to a file resource as part of a trigger event) Let’s look at a quick example from the very popular UnrealEd (version 3.0) showing the power of this kind of trigger-based editing. In many games, when an actor is shot by a weapon, we frequently want to launch a resulting behavior of some kind. For a shoot trigger, a trigger that trips when it has been shot by a projectile weapon, we want to launch a behavior—maybe a further scripted event—or maybe we want to display a simple text message. Figure 6-5 shows that for an assigned shoot trigger type (TT_Shoot), when the trigger is tripped, a text message will be displayed: “Ouch, you shot me!” This is a simple example to be sure, but it reveals the power of having a field-edited trigger system at your disposal for shaping actor-based behaviors. Many game developers create similar systems to enable trigger-based behavior editing. It’s important to remember that triggers can be edited in a field-edited GUI-type tool (like the UnrealEd example), edited directly in the script code, or edited in both.
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A BOUT THE AUTHOR Tom Meigs is a ga
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Brandon A. Nordin Scott Rogers Wend
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2 THE game design process begins by
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24 AFTER you’ve completed your pr
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54 FOR a game to be competitive the
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86 YOU now understand the developme
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Page 129 and 130: 108 UP to this point, we’ve cover
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204 Building Game Worlds 204 U L T
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216 ANOTHER new content horizon for
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238 THERE is a wide and growing ran
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Building Game Worlds 254 254 U L T
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266 AT some point in your skills gr
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274 Building Game Worlds U L T I M
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Building Game Worlds 278 FIGURE 11-
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286 THIS appendix includes useful r
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296 MANY types of software tools we
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304 TO assist you to further define
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310 I’VE gathered together a few
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322 AS a point of reference and as
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Building Game Worlds 336 Baseball s
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