How to use Masks with Reflection/Refraction in Cinema 4D


Starting with Corona Renderer 6, reflection and refraction now can be taken into account when using certain Corona masking elements (ID, Mask, Wirecolor), making propagation of masks through Corona materials possible. This means that you can now select whether the material can show up in masks as before (displaying anything behind it), not cover masks of objects being only reflected, not cover masks of objects only being refracted, or not show up in masks at all.



Propagation of masks can be achieved through selecting the preferred behavior of the reflective or refractive material in the Corona Material's Advanced options in the visibility tab, from the Propagate masks dropdown menu: 



Propagation Types


The following propagation types are available:


    • Never - Render elements are never propagated through this material, i.e. this material is always visible in masks.


(In this example 'Never' is enabled on all materials)


  • Through Reflection - Render elements are propagated through this material if reflection occurs, i.e. this material will only show masks of reflected objects, not those refracted.


(In this example 'Through Reflection' is enabled for reflective materials only)


  • Through Refraction - Render elements are propagated through this material if refraction occurs, or refracted from it, i.e. this material will only show masks of refracted objects, not those reflected.


(In this example 'Through Refraction' is enabled for refractive materials only)


  • Always - Render elements are always propagated through this material, i.e. this material is never visible in masks."


(In this example 'Always' is enabled for the mirror, vase, and table)


  • Always without Scattering - the material is not visible in masks at all, i.e. render elements are always propagated through this material directly without being affected by it.


(In this example 'Always without Scattering' is enabled for the mirror, glass, and table)


  • A summary of all available masks options:



Note: You will notice reflectivity in masks when propagation of masks is set to "Always" for a material that has no reflection or refraction. Preferably, the "Always" option should be used for materials that need both reflective and refractive propagation of masks. This happens to materials that have any diffuse value (color other than pure black). So for example, it will happen to white walls even if they do not have any reflectivity. This is because currently, Corona does not treat reflections differently than diffuse light bounces, so in masks, a diffuse object will look similar to a reflective object with a very low reflection glossiness value.