Page 11: Lights, Camera, Action!

On the next pages, we’ll talk about viewing (how the camera transforms the world to the screen), materials (how objects determine their color), lighting (how materials respond to the room’s brightness), and animation (how objects move).

Each of these pieces is a core topic in computer graphics. We will want to understand the concepts and the methods, to see how they are embodied in a high-level API, and then to practice using them via the high-level API.

For the first pass, we’ll look at each with a different level of detail.

For viewing: we’ll examine the problem of how we make a transformation from points in the world (scene coordinates) to what we see on the screen (screen coordinates). In computer graphics, we often consider this in two steps: the camera transformation (how we place the camera in the world) and projection (how the camera reduces 3D to 2D). As a metaphor, think of a camera in the real world. There is the positioning and aiming of the camera (the camera transformation), and the imaging that the camera’s lens does to “transform” from the world onto the film (or sensor).

Importantly, both of these aspects of viewing are simply homogeneous transformations that we can compose with other transformations.

With Three, the camera and projection are combined into a special object called a Camera. A Camera is like any other object (it is a type of Object3D): it has a transformation that places it in the world. A camera contains the projection transformation, while its position in the scene defines the viewing transformation.

Lights in Three are also special objects that we place in scenes. Lights don’t do much themselves: they just provide data to materials so the materials can determine how they should appear. However, this is still an important role: if there are no lights, we can’t see the materials.

Materials are the abstraction of how objects should appear. You can think of them as the “stuff” the object is made of. It could be shiny red plastic, or dark wood. Materials connect the object’s shape to the lighting to determine how the object should appear. They are basically responsible for determining the colors of things.