Ray casting

What is Ray Casting?

Ray casting is a method for calculating Field of Vision where rays are traced from the center of a source square to a select number of destination squares. Squares are marked as visible as the rays pass through them, and walls will block the rays.

There are a few ways to decide where rays are to be cast:

• Every potential destination -- This method is very slow, but results in a crude approximation of Shadow casting.
• Every square along the perimeter of the area being checked for Field of Vision -- This is faster, but causes an increasing number of artifacts as the radius increases.
• A fixed number of rays as regular intervals -- Provides a tweakable knob that trades off between accuracy and speed.

Advantages

• Easy to implement
• Builds intuitively on Line of Sight algorithms.

Disadvantages

• Slow compared to other methods. Even when casting only a few rays, squares close to the source will be visited many times.
• Many artifacts, even in common situations

How do I implement it?

• Ray-Tracing Field-Of-View Demo
• A Bucket Of LOS
• LOS by Odd
• Line of Sight - Tobias Downer
• Simple and accurate LOS function for BlitzMax

What games use it?

Moria

What libraries implement it?

libtcod contains an enhanced version of perimeter raycasting with a post-processing step removing most artifacts and making it equivalent to shadowcasting.