All images from The Magic of Houdini by Will Cunningham. Reprinted with permission.

This is the next-to-the-last in a series of excerpts from the Thomson Course Technology book The Magic of Houdini by Will Cunningham. This month, VFXWorld readers will continue to learn the basics of the dominant tool that has been used in the creation of some of the most awe-inspiring animation and cinematic effects ever made.

Motion blur is an integral part of almost any rendering that attempts to be photo-realistic. Even non-photorealistic rendering will usually use motion blur to avoid a choppy look. Mantra supports several types of motion blur and generally has good overall motion blur support. The following exercises take you through the different types of motion blur and review some controls regarding the ever-present quality versus speed choice.

Motion blur can be controlled in two places and, by default, uses a system of inheritance for ease of setting motion blur on all your objects. Geometry objects have their Motion Blur set to Inherit Behavior by default and this has two meanings. The first is that it will inherit the motion blur used by its parent, if it has one. The second is that it will inherit what the "global" Motion Blur type as specified in the ROP. Because the default is Inherit Behavior, you can actually set the type of motion blur for all your objects just by setting it in the ROP's Motion Blur parameter. The ROP can also be used to globally turn on and off the motion blur. As it turns out though, it is very rare that you want to turn on motion blur for everything in the scene. You will most generally be controlling the blur on a per-object basis, which is what the remainder of this topic covers.

[Figure 1] The zooming cube with no motion blur.

Transformation Blur
First, you learn how to get transformation type motion blur working.

1. Load the file MotionBlurStarter.hip and go to frame 5. You will bear witness to a fascinating, flying cube moving through the view.

2. Go to a frame where the cube is in view. In the Object viewport, render using the fast_mantra ROP. You can use the quick launch under the viewport or the Render button on the ROP itself if you prefer. Figure 1 shows you the result.

3. Ooooo, you may think. A shiny cube with a shadow is not all that impressive. In the Render tab of the Flying_Cube object, set the Motion Blur parameter to Transformation Blur Only and render it again. The Ooooo turns to Woooo as you can now see some pretty good blur. But, it is a little too noisy as shown in Figure 2.