3ds Max 2012 Bible - Kelly L. Murdock [397]
Editing Curves
When an object is moving through the scene, estimating the exact point where its position changes direction can sometimes be difficult. Function curves provide this information by presenting a controller's value as a function of time. The slope of the function curve shows the value's rate of change. Steep curves show quick movements. Shallow lines are slow-moving values. Each key is a vertex in the curve. Function curves are visible only in the Curve Editor and the Track Bar layout.
Function curves mode lets you edit and work with these curves for complete control over the animation parameters. Figure 37.10 shows the Position curves for a sphere that moves about the scene.
FIGURE 37.10
Function curves display keys as square markers along the curve.
Inserting new keys and moving keys
Function curves with only two keys have slow in and out tangents, making the animation start slow, speed up, and then slow down. You can add more curvature to the line with the addition of another key. To add another key, click the Insert Keys button, and then click the curve where you want to place the key.
Tip
Keep the total number of keys to a minimum. More keys make editing more difficult. •
If the curve contains multiple curves, such as a curve for the Position or RGB color values, then a point is added to each curve. The Move Keys button enables you to move individual keys by dragging them. It also includes flyouts for constraining the key movement to a horizontal or vertical direction.
To scale keys, use the Region tool; you also could use the Keys⇒Scale Keys–Time command to move the selected keys toward or away from the current time. The keys move only horizontally. The Keys⇒Scale Values command is used to move the selected keys toward or away from the zero value. The keys move only vertically.
Tutorial: Animating a monorail
As an example of working with function curves, you'll animate a monorail that moves around its track, changing speeds, and stopping for passengers.
To animate the monorail using function curves, follow these steps:
1. Open the Monorail.max file from the Chap 37 directory on the CD.
This file contains a simple monorail setup made from primitives.
2. Click the Play button, and watch the train move around the track.
As a default, the Path Constraint's Percent track has a Linear controller that causes the train to move at a constant speed. To refine the animation, you need to change it.
3. Open the Track View–Curve Editor by first selecting the train object in the scene and then right-clicking and choosing Curve Edit from the pop-up quadmenu. The Track View-Curve Editor window opens and shows the controls related to the object in the scene you have selected. Click the Assign Controller button or right-click and select Assign Controller from the pop-up menu to open the Assign Float Controller dialog box. Select the Bézier Float controller, and click OK.
Note
If the Objects track isn't visible, open the Filter Tracks dialog box and make sure the Objects option is enabled. •
4. Click the Play button. The train starts slowly (represented by the flattish part of the curve), accelerates (the steeper part of the curve), and slows down again (another flattish part).
Tip
When “reading” function curves, remember that a steep curve produces fast animation, a shallow curve produces slow animation, a horizontal curve produces no movement or value change, and a straight curve produces a constant animation. •
5. You need the train to stop for passengers at the station, so click the Insert Keys button (or right-click and choose Insert Keys) and add a key somewhere around frame 115 when the train is near the dock.
6. Select the newly created key, and choose the Move Keys Horizontal button from the Move Keys flyout. Hold