AFX and Bottle Rocket Science

Today is the 4th of July, Independence Day here in the United States, where a big part of the celebration is fireworks. A few weeks ago, with the 4th holiday approaching, Matthew Durante and I decided to see what kind of fireworks effects we could come up with using AFX. Here are the results in movie form and some images:

Fireworks Movie (AVI) <4mb> -- silent
Fireworks Movie (QuickTime) <3.75mb> -- silent

At first we attempted to pull this off in stock AFX 1.0.2. I got some good results attaching particle emitters to multiple debris effects, and Matt made some nice bursts using particles on paths, but we quickly realized that we lacked a good flexible way of moving effects in a ballistic fashion.

Instead of creating a monolithic fireworks effect, we wanted to find a way to harness the kind of physical forces at work in real fireworks and apply them to the movement of any AFX component effect. To do this, Matt had a clever idea for something we call ForceSets. In much the same way that AFX assembles multiple component effects into a bigger compound effect, it also groups individual forces into one or more ForceSets. From there, you can link other AFX effects to specific ForceSets which will then influence their motion in a physical way. You can think of each ForceSet as a separate little universe of forces which can fade in and out over time. Assigning an effect to a ForceSet causes its movement to be steered by the collection of forces in the ForceSet. (We are just using simple linear forces, nothing rotational, and no collision response, but this is enough for decent fireworks.)


With a prototype implementation of ForceSets in place, Matt went off and researched fireworks and designed the fireworks display captured in the movie. What you see here is mostly achieved using stock AFX 1.0.2 with the addition of ForceSets, however, the results are still highly experimental. As a whole the complexity of the fireworks display seriously pushes the software to the limits and beyond.

From here, we'll use what we've learned from this experiment to implement production-ready ForceSets to be included in a future update of AFX. We think the ForceSets will turn out to be very useful in a wide variety of effects beyond fireworks.

Happy 4th of July!