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Here you specify which channels you want to calculate with the mesh – the appropriate information is extracted from the fluid particles (please also see → “UVW Mapping” in the “Texture” section). The channel's data can be made visible in the viewport with the mesh node's Display > Particle channel option.
Weight
Weight maps are not listed here, because they are active by default. Their main purpose is the creation of transition effects between differently coloured fluids ("fluid mixing"):
- A mesh can store up to 10 weight maps from different emitters/domains.
- The names are "FluidWeight0" → "FluidWeight10".
- The weight channel is of type "float".
- Weight maps are also available in Alembic files.