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The Source controls the emission of fluid and where the fluid emits from, so that the simulator knows where in 3D space the fluid can be born.

An Emitter can be geometry and/or particles, and is what actually emits the fluid inside the simulation grid. The emitter(s) must be selected by the Source in order to emit fluid inside the simulator, unless you are using the Initial fill option in the simulator’s settings, or specifying a geometry to do an initial fill with liquid.

The Source also contains its own settings that determine how much fluid is emitted, what is emitted, and so forth. A Liquid Source can be used to emit fluid into a Liquid Simulator using Liquid FLIP particles, or any of the Source's Grid Channel options, and it can also emit fluid for multiple channels at once.

This includes emitting options such as RGB color and Viscosity, as well as emitting secondary particle types like Splashes, Mist and Foam.

You can use the Liquid Source to emit FLIP particles into Liquid Simulators.

You can emit fluid from geometry or from particles. The fluid can be emitted from the surface, or from the entire volume of emitting geometry. Particles can emit from a spherical shape, or from instanced geometry shapes. Note that the viewport gizmo of the Source does not emit fluid itself - you have to first pick the geometry or particles you would use as emitters in the Source's list.

You can emit any fluid particle channel and you can emit many channels at once. Additionally, you can emit different particle types from the Source. If you want to emit unevenly only from some areas or volumes of the emitters, you can use a Mask for each of the emission channels. Also, note that if Emit Mode is set to Volume Brush or Volume Inject and the Mask uses Explicit Map Channel or Vertex Color Channel mapping, then the Mask will be applied on the whole volume, based on the closest geometry surface.

Additionally, each channel can have one or many Discharge Modifiers. They allow you to gain more precise procedural control over how the fluid gets emitted. Discharge modifiers vary the emission over different parts of the emitter depending on properties of the emitter - e.g. the direction of its normals, the speed of movement at each point of an animated emitter, etc.

also use textures as masks for each of the emission channels, to create more interesting emission behaviors, with more variation. Specifically, Masks make it possible to emit unevenly from only some areas, or emit unevenly from the entire volume of an emitter.

Additionally, each channel can have one or many Discharge Modifiers.  They can give you more precise procedural control over how the fluid gets emitted.

Discharge modifiers vary the emission over different parts of the emitter, depending on the properties of the emitter - e.g. the direction of its Normals, the speed of movement at each point of an animated emitter, etc

Emit Mode | ifnotsolid – Specifies the way the objects in the Emitter Nodes emit fluid.

Surface Force – The surface of the emitters will eject the selected fluid channels along the geometry normals. In this mode, the discharge is named Outgoing Velocity and it specifies the speed of the emitted fluid in units/sec. The displayed units will change accordingly if the scene units change.

This mode can work with both Solid and non-Solid emitters. If you use a Mask for the discharge in Surface Force mode, white areas of the emitter's surface will eject fast fluid, while darker ones would emit more slowly. Black areas will not emit at all.

Volume Brush – The fluid inside the volume of the emitters will gradually change towards the selected channel values. When this mode is selected, the discharge is named Brush Effect (%) and it specifies the rate at which the transition takes place. When Brush Effect is 100%, the fluid will immediately reach the selected channel values, and if Brush Effect is less, it specifies how close the fluid values will get to the values from the Source over 1 second. E.g. if the Temperature inside an emitter's volume is 1000 and the Source emits Temperature 2000 with Brush Effect of 80%, then after 1 second the temperature will have risen to 1800. This mode is useful for creating standing volumes of fluid with a high Brush Effect, or alternatively - to slowly convert the fluid inside the volume of the emitters to the values selected below over a period of time. Note that you can both increase or decrease the values of the fluid channels in Volume Brush mode. When Brush Effect (%) is 0, then the Source has no effect.

This mode requires that all selected emitters are set into non-Solid mode from their Per-Node Properties. If you use a Mask for the discharge in Volume Brush mode, white zones in the volume will have the Brush Effect you have specified, while darker zones will use a smaller Brush Effect. Completely back zones in the mask would not be affected at all by this Source.

Volume Inject – The volume of the emitters will discharge the selected fluid channels with added pressure. When this mode is selected, the discharge is named Inject Power and it specifies the added volume of the injected fluid per second. This mode is useful for getting explosive discharge. Inject Power can be negative, in which case the Source will suck in and delete the fluid.

This mode requires that all selected emitters are set into non-Solid mode from their Per-Node Properties. If you use a Mask for the discharge in Volume Inject mode, white zones in the volume will have the Inject Power you have specified, while darker zones will use a smaller Inject Power. Completely back zones in the mask would not be affected at all by this Source.

Inject Power / Brush Effect (%) / Outgoing Velocity | discharge / brusheffect / outvel – These parameters control the strength of the source. Check Emit Mode for more info.

Mask | dmap, usedmap – Allows you to vary the Outgoing Velocity, Inject Power or Brush Effect (%) over the surface or the volume of the emitters. White areas of this map will have the strongest discharge, while black areas of the map will not discharge at all. The individual fluid channels can also be modulated using dedicated maps from the options below. See the info on the Emit Mode option above for more info on how the Mask affects each mode.

Modifiers |  dmoddisch – Discharge Modifiers can be attached here in order to affect the Outgoing Velocity, Inject Power or Brush Effect (%) parameters.

Noise | noise – Varies the Outgoing Velocity, Inject Power and Brush Effect (%) across the surface or the volume of the emitting geometry or particle. The variation also changes over time. This is a shorthand for using an animated noise in the Mask slot.