"Linear" is a two-dimensional emitter in the shape of a straight line. Emitters define the point of particle creation in 3D space, while the particles are part of the "Fluid" container. Emitters can be scaled, rotated, and translated like objects; an arrow indicates the direction of emission.
RealFlow Scene
In RealFlow | Cinema 4D it is possible to use multiple "Scene" trees in the same project:
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