= How to choose between liquid simulation types =

== Overview ==

Houdini has a few different ways of simulating liquid:

- [Particle fluid|pfluid_solver] -- Simulates the physical motion of many particles, then wraps the particles in a surface.
- [Sign distance field|fluid_solver] -- Simulates movement between points in an enclosed box.
- [Ripple solver|ripple_solver] -- Simulates the propagation of waves through a surface.

Each of these different methods has unique properties that make them more or less suited to simulate different types of fluids.

== Comparison ==

=== Particle fluids ===

- Are not constrained to the inside of a box. Can move freely anywhere in the scene.

- Can separate, be concave, splatter.

- More prone to spray than sign distance field.

- Surfacing between particles leads to "lumpy porridge" look unless you use a huge number of particles.

- Stray individual particles do not surface well. You'll probably want to suppress stray particles.

- Particles need to "settle" into shape from their initial placement. You'll probably want to pre-roll the simulation to allow settling.

=== Sign distance field ===

- Simulates a box of liquid (e.g. water).

- Can separate, be concave.

- More viscous than particle fluid, tends to slosh rather than spray.

- Smoother surface than particle fluid.

- Does not need to settle.

=== Ripple solver ===

- Simulates waves changing the height of a surface.

- Waves can rebound against edges. You can paint attributes to create areas of fast, slow, or no wave propagation.

- Waves cannot be concave -- only displaces "height" of points on the surface.

- Useful for simulating ocean surface.