FEATURE IN DEVELOPMENT STAGE
Preview image by Xpert Mihai of www.maxwellzone.com
Traditionally, having a dielectric object enclosed inside another dielectric object (like a liquid inside a glass) is a complex geometric situation due to the difficulty in defining the surface that delimits those mediums. As the liquid fills the entire volume leaving no gap, that surface limit becomes geometrically difficult to define with polygons. The typical approaches to this situation, and that don't produce a correct result, are:
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Modeling the glass and liquid bodies with coinciding faces produces precision errors in the coinciding walls
Preview image by Xpert Mihai of www.maxwellzone.com
The "infinitesimal gap" solution
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So far, the only way to overcome this situation and produce a correct result was the "infinitesimal gap" that is explained in this page: Tips and Tricks: Liquid in a glass.
This method involves the liquid body being completely enclosed in the glass body, which doesn't have inner walls where the liquid exists. This way there is only one single wall, instead of two, to define the limit area between the glass and the liquid medium. The method also involves a third material - glass exit material - over the liquid upper surface to provide the correct order for the rays exiting the glass medium in certain directions.
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The "infinitesimal gap" method was the only way to ensure every ray enters and exits the mediums in the correct order
Nested dielectrics
NEW IN MAXWELL V3.2
The best way to overcome this situation is by using the nested dielectics approach. Using this approach, two dielectric bodies can overlap and the render engine can automatically "boolean" them in render time and remove the surplus volume leaving just one single polygon wall, and assign the proper material for that single wall depending on the direction of the incident ray.
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In render time, the overlapping liquid volume gets automatically removed, leaving one single face and the materials properly assigned with respect to each ray direction (right)
What if we add some ice cubes?
If we want to throw some ice cubes into the liquid, we will end up with the a similar situation: inside the ice cubes' volume there exists at first two different materials coexisting (liquid and ice), which is not what would happen in the real world, where only ice fills that space. In this case we need to assign a higher priority (lower value) to the ice and a lower priority (higher value) to the liquid.
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