Masking objects allow you to shape your fluid volume by cutting out particles. The entire process is similar to Boolean subtraction operations, but requires a certain workflow.
The blue area should be filled with particles, the white areas will cut aways.
To achieve the look from the image below go through a few steps. In the first step, create four cubes, arrange them, and specify the one you want to fill with particles (named "Fill_Object" here).
- Add a "Fill" emitter and drag the "Fill_Object" cube to the emitter's "Body" slot.
- Set the emitter's "Fill Mode" to "Fill non Solid Volume".
- "Fill Volume" must be active.
- Enable the emitter's Mask > From Collision Objects option.
Time to adjust the objects:
- Add "Collider" and "Volume" tags to all four objects – the "Collider" tag tells RealFlow | Cinema 4D that there is an interacting object.
- Select the "Fill_Object" cube's "Volume" tag, and set "Volume Mode" to "Solid Outside".
When you reset the scene you will see that the volumes of the three remaining cubes haven been used as a mask to clip the particles. This way it is possible to create complex shapes without having to model an appropriate container.
If you want to change the mask simply move or delete cubes or make them inactive.