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Encoder ANSI/AIM Code 128 in Font Smoke trails

The last effect we ll look at in this chapter is smoke trails. It s quite a performance-intensive effect, and that gives us an opportunity to look at few new optimization techniques. Run the SmokeTrails SWF in the chapter s source files to see this effect in action, as shown in Figure 6-28.

Figure 6-28. Give the bullets smoke trails. How easy is it Just use a picture of some smoke and add it to the stage at the bullet s position. Rotate it, scale it, fade it, then repeat. When its alpha is zero, remove it from the stage. With a lot of these on the stage, it looks like a trail of smoke streaming from the bullet. Unfortunately, rotating, scaling, and fading alpha are among the most CPU-intensive tasks you can ask Flash Player perform. I ll show you how to cut down on any unnecessary animation and also how to use AS3.0 s Perlin noise feature to create a reasonably realistic-looking smoke image without needing to embed another photograph.

The smoke is an instance of the Smoke class from the package com.friendsofed. gameElements.effects. It basically just does two important things:

Creates a smoke pattern Animates the pattern by rotating, scaling, and fading it Here s the entire Smoke class: package com.friendsofed.gameElements.effects { import flash.events.Event; import flash.display.*; import flash.events.TimerEvent; import flash.utils.Timer; public class Smoke extends Sprite { private var _circle:Sprite = new Sprite(); private var _animationTimer:Timer = new Timer(96); public function Smoke():void { //Create the smoke using a Perlin noise effect: //1. Create a random "seed" number to start the pattern var seed:Number = Math.floor(Math.random() * 100); //2. Determine what color channels you want to use var channels:uint = BitmapDataChannel.BLUE|BitmapDataChannel.ALPHA; //3. Create a blank BitmapData to contain the noise var smoke:BitmapData = new BitmapData(5, 5, true, 0); //4. Use the perlinNoise method to create the noise //based on the random seed number and color channels smoke.perlinNoise (200, 200, 6, seed, true, false, channels, true, null); //5. Create a circle and fill it with the perlinNoise pattern _circle.graphics.beginBitmapFill(smoke); _circle.graphics.drawCircle(0, 0, 5); _circle.graphics.endFill(); addChild(_circle);

_animationTimer.addEventListener (TimerEvent.TIMER, animationEventHandler); _animationTimer.start(); addEventListener (Event.REMOVED_FROM_STAGE, removedFromStageHandler); } private function animationEventHandler(event:TimerEvent):void { _circle.rotation += 3; _circle.scaleX += 0.24; _circle.scaleY += 0.24; _circle.alpha -= 0.08; //Dispatch an event so that the parent can remove it if(_circle.alpha <= 0) { dispatchEvent(new Event("smokeFinished")); } } private function removedFromStageHandler(event:Event):void { _animationTimer.removeEventListener (TimerEvent.TIMER, animationEventHandler); removeEventListener (Event.REMOVED_FROM_STAGE, removedFromStageHandler); } } } The perlinNoise method is a fun effect that s used for making random blotches of pixels in an organic way, as shown in Figure 6-29. It can work well for things like smoke, water, and clouds. I ve also seen it used for generating random maps of continents and islands in games, as well as random 3D terrain, like mountain ranges.

The algorithms that produce a Perlin noise effect were first developed by Ken Perlin. His work won him an Oscar for Technical Achievement for its use in the 1982 movie, Tron.

Figure 6-29. A typical Perlin noise pattern This is the directive that creates the smoke pattern from the Smoke class: smoke.perlinNoise(200, 200, 6, seed, true, false, channels, true, null); There are a lot of parameters! But you really need to fully understand only these three: Parameter 4, seed: A seed is a number in an algorithm that triggers pattern. In this case, it s the catalyst for the random pattern of pixel blotches you see on the stage. You ll get a different random pattern by keeping all the other parameters the same and changing just this number. In the Smoke class, the seed is generated randomly, so each puff of smoke is slightly different. The seed can be any number; it doesn t need to be limited to a certain range or size. var seed:Number = Math.floor(Math.random() * 100); Any random number will do; only by experimenting can you see the effect it will have. And the seed number doesn t need to be random. It you keep it fixed at a specific number, you ll always generate the same pattern. Parameter 7, channels: This determines which colors are used. The Smoke class uses the BLUE and ALPHA channels. var channels:uint = BitmapDataChannel.BLUE | BitmapDataChannel.ALPHA; The ALPHA channel allows some parts of pattern to be transparent. The four channels to choose from are RED, GREEN, BLUE, and ALPHA. Delineate the channels with the bitwise or operator, which is the vertical pipe symbol (|) you can see between them.

Parameter 8, grayScale: This can be true or false. Smoke is usually a shade of gray, so I ve set this as true in the Smoke class. smoke.perlinNoise(200, 200, 6, seed, true, false, channels, true, null); Those are the most important parameters, but here s what the others do: Parameters 1 and 2, baseX and baseY: These set the size of the pattern. Parameter 3, octaves: This specifies how many times to repeat the noise pattern. More repetitions create a more detailed effect. Parameter 5, stitch. This creates a pattern in which the top, bottom, left, and right sides match. You can use this to make a continuous tiled background from one pattern. Parameter 6, fractal: If this is true, it will produce smoother looking gradients.