Pixar in a Box
Let's look more closely at how light bounces when it strikes an object. We'll cover reflected and refracted rays, direct and indirect illumination, and shadow rays. Refracted rays follow the path light takes when it passes through a transparent object, like a glass of water. Reflected rays follow the path light takes when it bounces off a shiny surface. Click here for more detail on refraction!
Want to join the conversation?
- I couldn't get the interactives on the two previous exercises to work. On the ray tracing exercise, a large part of the interactive would disappear, and on the Matching properties of lighting exercise, the interactive would just freeze up on me, making it unusable. I have tried reloading the pages multiple times, but I get the same result. Is this just me, or is it a problem with the site itself?(15 votes)
- would it be indirect illumination if you had an i-pad and the light coming from it was hitting you?(3 votes)
- No, that would be directly lighting since the light is coming directly from the source (the iPad) to you. Indirect lighting would be if you have a spotlight pointing at a wall, and the light reflected off the wall lights your face.(8 votes)
- What is the difference between reflected and refracted rays?(3 votes)
- On the previous interactive, the controls were in Spanish, is this just me or is everyone experiencing this?(4 votes)
- On the ray tracing exercise, it randomly turned to Spanish halfway through. I CAN"T READ SPANISH? Also, stuff was randomly disappearing every now and then.(3 votes)
- at2:00do people have to draw the reflections of other things on the cars, or can they just program a ray-tracer onto the them?(1 vote)
(introductory sound) In the previous video, we've talked about what color a point on a surface is by considering three factors: One, how much light falls on the point. Two, how the surface reflects light, and three, where the camera is. For the first factor, the ray tracer needs to determine if the point being considered is visible to the light source. This is actually pretty easy to answer. The ray tracer constructs a ray that starts at the point being shaded and launches off in the direction of the light source. These rays to light sources are called, naturally enough, shadow rays. Here's an example of an point that is visible to the light source, because the shadow ray doesn't hit anything but the light source. It's important to notice that only some of the light falling on a point comes directly from the light sources. This is called direct illumination. In the real world, some of the light comes from other objects in the scene as well. Notice that I can bounce light off this card, which you can see adds to the light hitting my face. This is an example of indirect illumination. As another example of indirect illumination, you can see a reflection of the tennis ball in the pool ball. A ray tracer can account for such reflections by sending another ray in the reflection direction. The direction of this reflective ray is determined by how a light ray would bounce naturally in the same way a pool ball bounces. This technique was used, for instance, in Cars 2 because reflections off shiny cars were super important to the look of the film. If the object is partially transparent, like this glass cup, the ray tracer can do a similar thing and launch a ray in the refracted direction. Refracted rays pass through an object while reflected rays bounce off of them. When the rays pass through an object, such as this glass, the rays bend in different directions instead of in straight lines, which explains why the image you see of me through this glass looks warped. (ding) The ray tracer can keep doing this, casting rays, sending out reflective and refractive rays to account for reflections, the refractions, and so on. Then, it uses all of these rays to determine the final pixel color. In this next exercise, you can test your understanding of these concepts.