ARTBLOG 9: Explosion Dynamics!

Kickstarter is over and what a campaign it was. WE MADE IT! WOOOOOO!

But seriously, celebration’s over, and it’s time to get back to work. When I started this project, I was a novice artist at best, and I’d like to think I’ve come a long way. Today I want to talk about the one of the hardest challenges for the uninitiated: FX animation! FX is a valuable skill; they do so much for gamefeel and player satisfaction. From residual dust when the character jumps, to large scale explosions, good effects go a long way toward making your project look polished. Usually you hire a guy who specializes in FX, but why hire a guy when your current art-team-of-one can struggle through it? So here I am, through the frustration and countless hours of trial and error to show you some of my findings. Let’s start with my most recent explosion.

Explosion

This explosion was a two day affair. We won’t worry about the color dynamics, that’s a little advanced for an introduction post. (That, and I’m still very new to it.) Let’s instead look at the anatomy of an explosion, and how it forms and dissipates. There are several rules to keep in mind when working on an explosion.

1.) Explosions are made up of particles. It seems to go without saying, but keeping this in mind will help during the birth, life, and eventual decay of the explosion. Everything with how the explosion works and why it looks “right” stems from this fact.

2.) These particles are in no way attached to each other. It’s important to realize that the solid shape you are drawing is just an illusion coming from the rapidly expanding particles. It’s not a single shape — it’s a bunch of particles overlapping. This means a dust cloud has no inherent elasticity. It will never decrease in size or expand to a higher level and bounce back, as is the case with most animation.

3.) All explosions emanate from a single point. Sometimes the direction can be affected by wind or environmental conditions, but we’re not worried about that for this example.

As you can see in the image below, in this explosion we have three points, but they’re really just 3 explosions happening in the same space and time-frame. Each influences the dust cloud in a similar way, pushing it outward from the particular explosion’s center. When you do this enough times, you’ll notice the animation will start to form itself. From the very first frame of animation, your explosion is set on an “optimal path.” The explosion has only one way that initial frame can properly expand. Your job as the artist is to see the pattern and to simply nurture the explosion.

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“But ZACH! That doesn’t make any sense! Can’t I draw an explosion any way I want?” While the artist definitely gets to decide on the style of the explosion, they do not get to decide how the explosion is formed. That’s the job of the laws of physics. once the first frame is drawn, the rest of that explosion’s course has been decided. In order to influence my dust cloud, I added compound explosions. It’s a neat effect, but not for the beginner. You need a thorough understanding of the process before you can problem solve for things like compound explosions.

The next thing to keep in mind is exponential deceleration. (Which may in fact be a redundant phrase, but I don’t really math….)

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Explosions will never increase in expansion speed. never. NEVER. In fact, the difference in size between frame one and frame two will never be matched again. From there it begins to decelerate very quickly. You’ll reach an almost standstill, but the further you take this, the better it will look. An explosion will also never stop. It’s always moving outward, it’s just that towards the end it becomes much less noticeable.

Slowing down the explosion will not be enough. Remember, as it slows, it becomes less specific. Those deep curves you had carved into the explosion become less and less, until the whole shape just looks kind of puffy. This is because while the particles are sent flying, they also begin to individually expand.

3This means the shape gets less bumpy and more rounded. The last step is deterioration. This part is tricky. You have your explosion. great, but now you have to get rid of it. The game can’t just cut to the explosion being gone, that wouldn’t look good at all. There are several solutions to the problem. Some people like to simply fade the explosion’s opacity to zero. I don’t like that usually. I like to deteriorate my clouds more organically. So, remember how I said a dust cloud is just a collection of particles? The trick is to break those particles up and then make them decrease in size as they drift away from each-other. In reality, the dust cloud would billow upward and the point would continue to smoulder, but that’s an awful lot of work, so getting rid of your particles in this way, while not 100% natural, saves you a load of animation time.

Explosions and fire can be pull-your-hair-out frustrating, but making one that works is the best feeling. It feels powerful, and it feels instantly alive. If you can hold out until your first success, you’ll be hooked! I’ll do one for fire in the future. See you next week!

~Zach