Area Lights and Soft Shadows

The Ray Tracer Challenge — by Jamis Buck (98 / 108)

👈 Chapter 17 Next Steps | TOC | Spotlights 👉

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 to the light source. This results in a boolean “yes/no” result, answering the question of whether the point is in shadow. For an area light, you must cast multiple shadow rays, and the answer is no longer “yes” or “no,” but an intensity value telling you how much shadow exists at that point.

To implement an area light, follow these steps:

Light sources are of many types, though. Read on for another one.

👈 Chapter 17 Next Steps | TOC | Spotlights 👉

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