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Reaction Manager

In event-driven animation, one object controls the animation of another. Say you want to rotate a Teapot object based on the orientation of another teapot. The two simplest ways to create a one-to-one relationship between the teapots are either to use an Orientation constraint or to wire the parameters of one teapot to the other.

The new Reaction Manager simplifies the wiring process and allows you to use a function curve to effect the change. An object that is animating at a steady pace can control the animation of another object based on this curve. The Reaction Manager provides accurate one-slider control over complex animations and rigs; for example, with it you can control the rotation of each bone in a long dinosaur neck using just a single slider.

Such setups are called Reaction controllers, logically enough. There are five different types of Reaction controllers: Position Reaction, Rotation Reaction, Point3 Reaction, Scale Reaction, and Float Reaction. Most of the setup of a Reaction controller is done within the Reaction Manager dialog, available from the Animation menu or by choosing it from the Alt-right-click Quad menu. The process is straightforward: you set up a master node to control any number of slave objects.


The Reaction controllers replace the Reactor controllers from earlier versions of 3ds max. Any existing Reactor controller will be converted to a Reaction controller in 3ds max 7.

Getting a Reaction

Let's work through the steps needed to get one object to react to another.

From the DVD, open the file entitled reaction manager start.max. The 3ds max file opens with two Cylinder primitives. We'll use the height of the first cylinder to animate the height of the second cylinder. We'll also put limits on how much the movement of the second cylinder will be affected.

Select the left cylinder and open the Reaction Manager (Figure 4.8).

Figure 4.8. Opening 3ds max 7's new Reaction Manager. It enables quick rigging of an animation relationship between two objects.

Set the master object: Click the Add Master button, click the left cylinder, and choose Object (Cylinder) > Height from the menu.

Now set the slave object: Click the Add Slave button, click the right cylinder, and choose Object (Cylinder) > Height from the menu (Figure 4.9).

Figure 4.9. The left cylinder is the slave; its height will react to that of the right cylinder. The first State is added to the States list.

Click the Create State button. Double-click to highlight each value and enter the following: State01 = 50; Cylinder02/Height = 50; State02 = 100; Cylinder02/ Height = 100 (Figure 4.10).

Figure 4.10. The second State will be added to the States list, and the values for each State and Height need to be changed.

The height of the right cylinder will have a range from 50 to 100. The height of the right cylinder will change when the height of the left cylinder is between 50 and 100.

In the graph, right-click each node and change both of them to Bézier Corner. Move the left node Bézier point up, and the right node Bézier point down (Figure 4.11). If necessary, do a Zoom Extents in the Reaction Manager to see the graph. The function curve graph determines how the right cylinder height will react to the left cylinder height when the height values are between 50 and 100.

Figure 4.11. The function curve is no longer a diagonal straight line. The reaction of the right cylinder height will follow the influence of this curve.

Turn on Auto Key and go to frame 100. In the Modify panel, change the left cylinder's height to 150. Play the animation (Figure 4.12).

Figure 4.12. The left cylinder's height changes from 30 to 150 over 100 frames.

At values below 50 and above 100, the left cylinder's height does not affect the right cylinder's height. Between 50 and 100, however, the right cylinder's height does change. Movement of the right cylinder's height varies according to the curve of the Reaction graph.

Open the file entitled reaction manager finish.max from the DVD and check your results.

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