Emitter blueprints

ObiEmitterBlueprints are assets that define physical properties of the fluid emitted by an emitter, such as viscosity and density. You can assign only one emitter blueprint per emitter, but you can define as many as you want (water, smoke, honey, blood, sand etc.) and switch between them at runtime.

All collision-related parameters of a fluid, such as stickiness or friction, are not controlled trough emitter blueprints, but trough ObiCollisionMaterials. Check out the collisions manual page for more info.

To create a ObiEmitterBlueprint, right click on any folder of your project and select Create->Obi->Fluid blueprint/Granular blueprint. Now we will go over all properties exposed by each one:

Fluid blueprint

Fluid particles will stablish density constraints between them, which will try to hold a constant density in the vicinity of each particle.


Maximum amount of emitted particles. The emitter will generate a particle pool containing this amount of particles, newly spawned particles will be taken out of the pool and destroyed particles will return to it for later reuse.


Resolutions from left to right: 1,2.5,5

This parameter controls the size and amount of particles used to represent 1 cubic meter -or square meter, in 2D- of fluid volume. The default value (1) will use 1000 particles per cubic meter. Higher values will cause the size of particles to decrease, so that more particles will be neeeded per volume unit.

Rest density

Density ratios from left to right: 1:1,1:1.5,1:3

Fluid density in kg/m3. This value is used to calculated the mass of each particle, at the current resolution. Particle mass is directly proportional to this value, that is, high density fluids will be made out of high-mass particles, and low density fluids will be composed of light particles.


Smoothing radii from left to right: 1.2,2,3

This sets the radius of the zone around each particle considered when looking for neighbours to calculate fluid density. It is a percentage of the actual particle radius. Larger values will yield smoother fluid, that will also be more expensive to simulate. A value of 1 (100%) will make particles only consider neighbours that are actually in contact with them. A value of 2 (200%) will extend the particle influce to a zone twice as big as the particle itself. As a rule of thumb, this value should be around 1.5-3.


Viscosities from left to right: 0,0.1,1

Viscosity smooths out the velocity field generated by fluid particles when moving. High values will cause the fluid to look thicker and flow slower, low values will make it look much lighter. As a rule of thumb, this value should always be between 0 and 1.5-2.

Surface tension

Surface tensions from left to right: 0,0.1,1

Increasing this value will make the fluid try to minimize its surface area, causing spherical drops to form. Low values will let the fluid surface take any shape. Keep this value between 0 and 1.5-2.


Buoyancies from left to right: -1,-0.2,0.2

Controls the relative density between the fluid and the surrounding air. A value of -1 will cause the fluid to accelerate in the direction and rate specified by gravity (as it makes it denser than air). A value of 1 will cause the fluid to accelerate in the opposite direction (as it is lighter than air). A value of 0 will make the fluid ignore gravity.

Atmospheric drag

Drags from left to right: 0,20,50

Amount of air resistence. High values (e.g. 50) of athmospheric drag will cause particles near the fluid boundary to move slower, which can be used to model smoke and gases.

Atmospheric pressure

Pressures from left to right: 0,8,-8

Amount of inward pressure applied by air on the surface of the fluid. High values will (e.g. 5) will cause the fluid to be more compact. Low values will allow the fluid to expand easily.


Vorticities from left to right: 0,0.5,1

Amount of vorticity confinement, it will contribute to maintain vortical details in the fluid. Keep this value relatively low (0-0.5) for best effect. High values can introduce instability.

Granular blueprint

Granular materials are made of particles that behave like rigid spheres, which can be useful for sand-like effects (boulders, debris, etc). Their resolution and rest density parameters behave in the same way as their fluid counterparts.


Randomness from left to right: 0,15,30

Variation in particle size. This is a percentage over the base particle size dictated by the material resolution, so a value of 20 will mean particles will be between 100% and 120% of their base size.