FFSimulatorParticle

The FFSimulatorParticle provides a basic particle-based flow simulation. The Particle data is saved in two internal RenderTextures containing the particles' UV position, fluid amount, speed, and color.

The FFSimulatorParticle is initialized automatically as soon as the targeted FFGravityMap is fully initialized.

Flow Simulation

Each simulation step, the particles sample the FFGravityMap's flow texture at their position and move in their corresponding 'down' direction. A small circle is then drawn for each active particle to the targeted TextureChannel of the FFCanvas. Over multiple update steps, this results in a trail as the particle is moving down the surface.

Adding Particles to the Simulation

Compared the the FFSimulator particles have to be added to the FFSimulatorParticle directly instead of to a FFCanvas texture channel.

The particle-data textures behave similar to a First-In-First-Out (FIFO) buffer, meaning that older active particles may be overwritten by newer ones, if the internal particle-data texture size is too small for the amount of particles you are adding.

The next best section, new particles are added to, is determined in the FFParticleUtil.Data.Request(Vector2Int size) method.

There are two approaches for introducing new particles to the simulation:

• ProjectParticles(): project particles onto the renderer using a FFProjector. This renders the surfaces to a small section of the particles data RenderTextures using the projector's view-projection matrix. The UV coordinates of the rendered fragments within the projector's frustum are used as the new particles' starting position.
• AddParticles(): define the position, fluid amount, speed, and color of the new particles, and upload it to the data-buffer texture. However, the particle's position is the UV position within the FFCanvas texture atlas, and thus non trivial to compute. FFCanvasExtensions contains two helper functions for computing these texture atlas UV positions (AtlasTransformUV(), TryGetCanvasUV()).

Checkout FluidFlow/Examples/Scripts/SimpleDrawParticle.cs for basic examples of these two approaches.

Flow Speed

Each simulation step, particles must only move one pixel, to ensure that they do not step into a different UV island. Thus, the flow speed is directly dependent on the update frequency.

As texel-density on the mesh can vary, the particles can appear to move faster/slower on parts of the mesh.

Performance

A timeout can be used to halt simulation after a specified amount of time after the last edit to the particles in order to save computation cost. You can reset the timeout manually using the ResetTimeout() method.

In general, the performance impact of the simulation is proportional to the size of the particle data textures, and simulation update frequency.

Fields

Check the tooltip hints for additional information of individual fields.