Target particle control of smoke simulation

User control over fluid simulations is a long-standing research problem in computer graphics. Applications in games and films often require recognizable creatures or objects formed from smoke, water, or flame. This paper describes a two-layer approach to the problem, in which a bulk velocity drives a particle system towards a target distribution, while simultaneously a vortex particle simulation adds recognizable fluid motion. A bulk velocity field is obtained by distributing target particles within a mesh, then matching control particles with target particles; control particles are given a trajectory bringing them to their targets, and a field is obtained by interpolating values from the control particles. A detail velocity field is obtained by traditional vortex particle simulation. We render the final particle system using stochastic shadow mapping. We spend some effort optimizing our processes for speed, obtaining simulations at interactive or nearinteractive rates: from 70 to 500 milliseconds per frame depending on the configuration.