How to fly among hundreds of 3d spheres drawn on a 2D canvas in pure JS without WebGL nor ASM.
All the logic is done in the class painter of the file ray.painter.js.
The above image is a good illustration of how ray-tracing works. Just place a screen in front of a camera and cast a light's ray through each pixel. If this ray hits a sphere, you can determine the pixel's color by looking at the angle of incidence for that collision. To get more realism, you can make the ray bounce until it reaches a light source or dies in the darkness.
You can see at the WebGL version of this demo, which is much faster!