portals

Portals (or exit portals) are objects that help LuxRender render interior scenes more efficiently. Their function is to indicate where openings like doors and windows are located, so that no rendering power is wasted on exploring light that does not enter the scene.

Portals currently only works for infinite light, sun light and sky light.

Portals do not emit light and do not contain any visible geometry. A scene with and without portals should look identical, except that the one with portals renders faster.

To create a portal, just create a rectangle with its normal pointing inward in all window openings and assign the portal material.

The process behind portals is quite complex (probability/sampling computations) and grows linearly with the number of portal shapes. This means that if a scene contains many windows, it may be more efficient to use a few big portals instead of individual portals for each window.

Adding portals to a scene may result in lower number of samples being calculated, but because the samples contribute more to the image the rendering process will be faster anyway.