Rule-based control of animation and particle time, is one of the most powerful Non Linear Animation (NLA) features of thinkingParticles.
In the example animation shown below, a door opens whenever a particle approaches. This animation doesn't use a standard linear keyframe animation approach. Particles do in fact control the animation of the door!
Animating this door by hand would mean, that you have to decide, when and how fast the door needs to open. However, the particle system can be changed at any time; this would mean re-animating over and over again, which could easily be avoided, by using the NLA approach in thinkingParticles.
An ObjectToParticle node was used to turn the door into a particle. Now that the door is a particle, it's possible to use any rule based methods to control the animation by a condition or operator. In the case shown below, a simple distance operator was used to measure the distance between the door and the approaching particles. The door opening is fully automatic. No keyframe is necessary, since the animation is controlled by rules alone.
Another remarkable feature, is the ability to control the speed at which the door opens by setting the particle velocity. Faster particles will force the door to open faster. Another idea would be to open the door, based on the impact of the particles. If 300 particles hit the door, the door will open. Once again, you've seen how thinkingParticles offers limitless possibilities, for any dedicated CG artist.