CAP 211 - Interactive Design and Game Development

Chapter 45 - Raytracing and mental ray


This lesson discusses more about rendering scenes with realistic light in 3DS Max. Objectives important to this lesson:

  1. Raytracing settings
  2. Raytrace material
  3. Raytrace maps
  4. mental ray
  5. Shaders
  6. Caustics and global illumination

This chapter begins with what seems like a discussion meant to be confusing. Let's define some terms"

  • Raytracing - following rays of light through a scene to display how they would be reflected and refracted in the real world
  • Scanline renderer - the default rendering engine in 3DS Max as it is shipped
  • mental ray - an optional render engine, supplied with 3DS Max, that is slower than scanline, but does a more thorough job of rendering traced light

Many settings in 3DS Max are affected by which render engine you have selected as the current default. Yes, this means that you can set mental ray to be the default engine, or you can leave scanline as the default. In this sense, default just means the one that will be used unless you change it.

The text offers images on page 1054 of a scene that has been rendered with and without raytracing. The images are unenlightening. A better example of the effect is visible on this tutorial about using raytraced material.

The text warns us that we should set a value for either Maximum Depth or Cutoff Threshold to keep rays of light from being traced to infinity, as would logically happen if two reflective surfaces face each other. (If you don't understand, hold a mirror in front of another mirror, place something between them, and marvel at the infinite regression of the image reflected between them.)

Page 1056 introduces the idea of excluding an object from the raytracer. Excluding an object from raytracing will speed up the render by the amount of time that would have been spent on that object. Open the Rendering menu and choose Raytrace Global Include/Exclude. You should be able to include or exclude any object in the scene (except those that do not render anyway).

The text tells us that raytracing takes color, reflection, refraction, and effects like fog into account when rendering a scene. This effect is increased by using raytrace materials in the scene, which reflect and refract more effectively than standard materials. There are several new settings for these materials, which are listed in the text. A tutorial will be enlightening.

Tutorial Notes and Questions

Tutorial 1 (Coming up roses):

  1. Open the indicated file. Some of the instructions are not clear (oh, really?) so I will point out some things. Before you do anything else, render the file and take a good look, otherwise you won't appreciate the raytracing effects.
  2. Once you open the material editor, you will want to know that the Type button is the one that says Standard by default.
    Note that you can't set a value for the Transparency option until you take the check out of the box beside it. Set the values as instructed.
  3. This one works as written. Pick a shade of green for the stems and leaves.
  4. You need to know that the Pick Material from Object tool is the eyedropper to the left of the material name. The Faceted option was turned off when I got to that part.
  5. The Tiling value that you set affects the width of the grain in the wood table. You may want to use a higher value than 20 to get thinner grain lines. Render at different values to see what looks better. Render at different Specular values as well. Note that the value for the table affects the brightness in the scene, which affects the way the vase looks as well.
  6. You can create a wallpaper as the text says, or you can use the one that is shown in the text. It is included in the chapter 45 folder.
    U-Coordinate Tiling did not appear as an option until I turned off Real World Scaling.
    I was also unable to drag the material to the wall plane. I was able to apply it to a selected object. To do this, you need to know that the wall is Plane01.

assign renderer rolloutThe second tutorial does not present anything new. We will move on to the material about mental ray, the second renderer that in included with 3DS Max. You can choose to use mental ray or the scanline renderer on the Assign Renderer rollout on the Render Scene dialog. (see image on the right) You can set mental ray to run with or without extended features under Preferences, as shown in the text on page 1064.

The text offers its usual list of settings that can be used with mental ray.

Tutorial 3 (Using caustic photons to create a disco ball):

  1. Begin by opening the specified file.
  2. In step 2, you are told to create a sphere in the Top viewport, near the top of the room (scene). Of course, that's nonsense.
    Question 1: If you follow the instruction, why must you then change the ball's position?
  3. In this step, after you select the Raytrace material, you will need to click the Go to Parent button to continue.

    Before you render the scene in step 5, you should animate the ball. Turn on Auto Key, and click the Select and Rotate button. Move the timeline to frame 30, and rotate the ball about 1 full turn. Then render only frames 0 through 30. This will still take several minutes.


  1. After you do the tutorial above, follow this link to better illustrated tutorial about making a caustic.
  2. Work together with at least one other student to do the tutorial.
  3. Turn in notes for the tutorial along with two questions and answers about it based on your observations.