Nested Dielectrics-嵌套电介质

Nested Dielectrics

Dielectric materials are anything non-metallic, and quite often, transparent. It is quite common to have transparent scene objects contained within others, such as a glass of water with ice. This represents a particularly interesting challenge for raytracing engines to render correctly, as there are three different material boundaries in this example: that of the glass, the liquid, and the ice. The challenge occurs where these boundaries meet.

OctaneRender® uses nested dielectrics to resolve the intersections at these boundaries and render the scene correctly. To do so, the objects with different IOR values must intersect and a priority needs to be assigned to the materials (found in the common tab of each material.)

To do so successfully requires certain concessions when creating scene assets, such as modeling each asset as “watertight” (meaning closed) and intersecting. In the case of the water in the glass, the water needs to be modeled so that it penetrates into the glass body, without protruding into the outside of the glass. (Modeling the water “accurately” will cause unsolvable ambiguities for Octane.) The ice cubes merely need to be in the glass volume and do not require any special care in this example.

Once the objects have been modeled in with these considerations, priorities are assigned to each dielectric material so that Octane can use nested dielectrics to render a correct result. Each material will need to have the proper IOR value assigned for what it is intended to represent. In this case: the glass (1.5); the liquid (1.335) and the ice (1.309).

The image below shows the correct result on the left, and with nested dielectrics disabled on the right:

PRIORITY

Priority is used to differentiate the different IOR volumes from each other. Priorities are numerically assigned lowest (-100) to highest (100), where the lowest would be the object or material having the least desired effect on the image. In the case of the water glass example, the water would be assigned the lowest priority (1), then the glass (2), and, finally, the ice (3). Priority is available in the Common tab of Octane materials, as illustrated below.