In the world of Flash design and development, there is very little that gives me as much giddy pleasure as playing around with particle effects. Over the next few blog posts, I plan to do a few tutorials relating to particle effects, but before I did so, I wanted to lay a little bit of a foundation and talk about the basic idea behind these effects.

In essence, a particle effect involves creating a single Movie Clip or Sprite and duplicating it, animating it, and randomizing it on the stage using ActionScript. This concept can be used to create randomized raindrops, snowfall, fire, smoke, bouncing balls, and even some more abstract effects.

Here's an excellent example of a fire particle effect using ActionScript 3.0:

Don't worry, we'll get to how to create these over the next few days. For now, I simply want to discuss how they work. In the fire example, I started by creating a simple fire particle, which was nothing more than a circle with a radial gradient applied to it. This is what that particle looks like:

I've zoomed in on the particle so you can get a good look at it, but for all intents and purposes, it's just a simple circle.

Once you've drawn this particle and stored it as a Movie Clip, everything else is done in ActionScript. In ActionScript, you would define:

• how the particle moves - In this case, it's easy. The fire particle will move upwards at a constant rate. Other types of particles may be a little more complex and require gravity calculations.
• the size and the opacity of each particle - Each particle, when it is added to the stage, is given a random size and opacity within a defined range.
• growth/decay rates - For the fire effect, each particle gets smaller in size as it rises. The rate at which is shrinks is its decay rate. Other particles, such as smoke particles, may get larger as they animate.
• boundaries - The most obvious boundary would be a boundary of movement. If you have a bunch of bouncing balls, the downward movement of a falling ball would be restricted by the floor.
• starting position - In the above example, each new fire particle is placed on the stage wherever the mouse cursor happens to be at the time it is instantiated. Other effects may call for a specific placement on the stage or even a random placement.
• et al - Depending on the effect you're going for, there may be any number of other variables or constants that need to be defined in order to determine the behavior of the particle in question.

The great thing about particle effects is that it's so easy to experiment with them. Throw in a couple of new numbers, add some gravity and some boundaries, or change the color or shape of your particle Movie Clip, and you'll discover entirely new effects that you may never have dreamed of.

So, now that I'm done blathering on about particle effects, in my next post, I'll actually show you how to get started implementing them.

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