Portal Material

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. MaterialsA set of attributes or parameters that describe surface characteristics. are a used to optimize the rendering of light sources, they accomplish this by helping the render kernel find important light sources in the scene. For example, in the case of interior scenes illuminated by an outside light source that comes in through windows, it can be difficult for the path tracer to optimize the light as it enters the interior environment. To help the path tracer find these light sources a polygon plane can be placed outside the window and then a Portal MaterialThe representation of the surface or volume properties of an object. can be applied to the plane, thus creating a “portal plane” (AKA Portals). This set-up will improve the quality of the light and increase the efficiency of the render.

In Figure 1 (modeled in Maya), a room is being prepared with a small, single window. This would be a difficult scene to light with a sun/sky or HDRIAn image which presents more than 8 bit per color channel unlike most common image formats. file with no lighting on the interior of the room. A single plane was placed over the window (highlighted in green) with the normal for the plane facing into the room (yellow arrow).

Figure 1: A plane is placed outside an opening in a polygon room, this plane will serve as a surface for the portal material.