62 ◾ 3D Animation for the Raw Beginner Using Maya
multiple objects, and since the light continues to reflect and refract, going off in multiple directions. The one thing that the renderer can do to save a bit of time is to determine what we call “hidden surfaces,” and not performing any calculations about their light properties. This process of calculating the movement of light in a renderer like mental ray is called “raytracing.” Here is the major point. The more calculations that go into tracking light rays as they reflect and refract, the more mental ray is able to simulate and recapture the sense of depth in a scene by carefully assigning each pixel on the display its own individual light properties. This means that sometimes, in order to get the apparent 3D visual result we want, each frame might take a long time to render because it involves tracking photons as they bounce many times around the scene. At some point, we stop calculating the movement of light rays as they move through a scene. This can be carefully controlled by choosing: any Main Menu → Window → Rendering Editors → Render Settings For mental ray, choose raytracing. For the Maya Software renderer, choose Raytracing Quality. This is the frustrating part for us as we learn to use Maya on a conventional desktop or notebook computer. At render time, we find ourselves having to compromise between visual quality and computational tractability. Rendering, not modeling, is what demands a lot of memory, powerful processors, and a high-end graphics card. Renderers like the Maya Software Renderer and mental ray are called “photorealistic” because the main goal of using one of them is to create a rendering that is as close as possible to what looks like a photograph of the real world. Most renderers used with 3D modeling software are considered photorealistic and use raytracing, but it is not true that raytracing and photorealism are the same thing. In principle, raytracing is just one technique that can be used to create realistic renderings. There are times when 3D modelers might want to use nonphotorealistic renderers. We might, for example, want to turn a scene into something that looks like a line drawing and use it in a product development document. Or, we might want to “toon” the scene by flattening it into a 2D image; we will look at a way to simulate tooning in Maya later in this book. (But we still use a photorealistic renderer.) One last remark: As we will see later, it is not always best to calculate raytracing as far as possible, as this sometimes washes out shadows. Somewhat ironically this has the opposite effect from what we desire—by removing the visual sense of the geometric relationships between objects in a scene. Glass in mental ray In Figure 3.19, we are selecting a material from the mental ray list. It is called mia_material, and it can be easily tailored to create different looks. This material, along with the others that begin with “mia” can be used to create almost any sort of reflective or semitransparent