The Ray Tracer Challenge

Area Lights and Soft Shadows

Your ray tracer currently implements point lights, which exist at a single point and have no size. These lights cast sharp, crisp shadows with perfectly defined outlines. But in the physical world, a point light doesn’t actually exist. Light sources have dimension, and the shadows they cast tend to be fuzzy around the edges as a result.

Consider the illustration, which compares shadows cast by a point light (on the left), with shadows cast by an area light (on the right).

Those blurred shadows don’t come cheap. Recall from Chapter 8, ​Shadows​, that your current shadow test casts a single ray from the point of intersection ...