mental ray lighting and rendering opens up a large range of possibilities within Maya. As with all rendering, lighting plays the primary role. We’ll cover mental ray rendering more in the next chapter; but because rendering and lighting go hand in hand, it’s tough to ignore it in this chapter. This section is a primer on mental ray light functionality.
Open the Render Settings window by choosing Window ⇒ Rendering Editors ⇒ Render Settings. If you don’t see the mental ray for Maya (or any other, such as the Vector) option in the Render Using drop-down menu, you need to load the plug-in. Choose Window ⇒ Settings/Preferences ⇒ Plug-in Manager to open the Plug-in Manager. Make sure Mayatomr.mll is checked for Loaded as well as for Auto Load to ensure that it loads by default.
Figure 10-37: The Maya Software render of the box of spheres scene
Two important functions that mental ray brings to the Maya table are caustics and global illumination (GI). Caustics is the scattering of light reflections off and through semitransparent objects, such as the light that shines on the ceiling of an indoor pool or the sunshine at the bottom of an outdoor pool. Global illumination is the effect of light reflected from one object to another. For example, if you place colored spheres inside a gray box and shine a light into the box, the walls and floor of that box pick up the color of the spheres. The light from the spheres reflects onto the walls and tints them with the spheres’ color. Furthermore, the light from the floor of the box bounces and helps illuminate the underside of the balls.
Figure 10-38: The mental ray for Maya render of the scene in Figure 10-37
For example, Figure 10-37 shows a scene file that has a dozen or so glass spheres inside an enclosed box. The box has four holes in the top, and two spotlights with shadows turned on are positioned outside the box, shining in through the holes. Figure 10-37 shows a typical software render. The spheres under the holes are visible, and the rest of the box is in shadow.
However, when rendering through mental ray for Maya (see Figure 10-38), the light that enters the box bounces around the scene and illuminates the other spheres. The color of the spheres also colors the area immediately around them due to GI. Additionally, the light shines through the semitransparent spheres and casts caustic highlights on the floor. (You can see the full effect in the color section of this book.)
Global Illumination: A downloadable PDF Exercise
Global illumination and caustics are both advanced lighting effects and won’t be covered in this book. However, a short GI exercise from a previous version of this book is available for download from www.sybex.com/go/intromaya2011. However, all the scene files for this exercise are on the book’s CD for your reference. Once you download the exercise, you can use Adobe Acrobat and the scene files on the CD to run through this living-room exercise, where you use simple GI techniques to explore this powerful rendering option in mental ray.
Image-Based Lighting
mental ray also brings image-based lighting (IBL) to Maya. This method of lighting uses an image, typically a High Dynamic Range Image (HDRI), to illuminate the scene using Final Gather or GI. Final Gather is a form of global illumination that relies on direct as well as indirect illumination. Direct illumination calculates the amount of light coming directly from lights in the scene and renders the result. However, it misses an important aspect of real-life lighting: diffuse reflections of light. Indirect illumination happens when light bounces off objects in a scene in order to reach and therefore light the rest of the scene—that is, diffuse reflections. Final Gather is typically a faster way than GI to get indirect illumination in a scene.
We’ll briefly touch on Final Gather here as we explore Physical Sun and Sky lighting in the next section. However, we’ll cover both IBL and Final Gather in depth in Chapter 11 when you light the decorative box model and apply displacement maps for its details.