Portals optimize rendering by helping the render kernel find important light sources in the scene. For example, interior scenes illuminated by an external light source coming through a window, can be difficult for the path tracer to optimize. Placing a PortalA technique that assists the render kernel with exterior light sources that illuminate interiors. In interior renderings with windows, it is difficult for the path tracer to find light from the outside environment and optimally render the scene. Portals are planes that are added to the scene with the Portal material applied to them. at the window opening improves light quality and increases rendering efficiency.


The following renders show a glass sphere in a room lit by light coming through a window. Both images were rendered for 500 samples. The left image does not use a portal and appears noisier than the right image which uses a portal.



Portal Set Up

The plugin supports the use of Modo Portals and geometry that has a Portal MaterialThe representation of the surface or volume properties of an object. applied to it. See Portal Material for more details.


The following example shows a room with a small window, which would be difficult to light using a Daylight Environment, or a HDRIAn image which presents more than 8 bit per color channel unlike most common image formats. in a Texture Environment.



To set up portals correctly, make sure that every window or opening in the environment is covered by a portal. The portal (or geometry normal) must be facing inward toward the interior. Don't block portals with other geometry such as glass surfaces.


Avoid using high polygon geometry with Portal MaterialsA set of attributes or parameters that describe surface characteristics.. A few simple rectangular planes are best because dense geometry can slow down rendering. It's possible to use a single piece of portal geometry to cover several openings, however, if the geometry is too large, it can reduce rendering efficiency.


NOTE: Portals will only work with the Path Tracing and PMC kernels. They are not supported by the Direct Lighting kernel.