BONUS CHAPTER 10

Using the Motion Mixer

The Motion Mixer lets you add several different animations to the interface, comprising both biped and non-biped objects. The animations then can be blended and transitioned between the loaded animation clips. You also can modify clips as needed.

Now that you've learned how to animate characters using a variety of techniques from Biped's Footstep and Freeform Modes to custom bone systems with IK solutions, it's time for you to explore Max's set of features that enable you to reuse animation clips between characters. This technique is called Retargeting, and it involves scaling the animation keys so a single character animation can be reused on other characters that are different in size and width.

Using the Motion Mixer

The Motion Mixer is a completely separate interface, shown in Figure 1. This interface is accessed using the Graph Editors Motion Mixer menu command. The same interface also is opened using the Mixer button found in the Biped Apps rollout of the Motion panel when a biped is selected. If the Mixer button is used, then the Motion Mixer opens with the biped already added as a track to the mixer interface.

FIGURE 1 The Motion Mixer interface shows each loaded animation on a separate track.

Learning the Motion Mixer interface

Along the top edge of the Motion Mixer interface are several menus and a row of toolbar buttons. Many of these buttons perform the same commands found in the menus. You also can access these commands using the right-click pop-up menus. The toolbar buttons are described in Table 1.

TABLE 1 Motion Mixer Toolbar Buttons

To the left of the interface, each track is listed under its controlling object or biped name. The small m button is used to mute a track, which removes its effect from the interface; and the small s button is the solo button, which displays only the animation clip on that track. The right end of the interface shows the weight value for each track. The small w button lets you edit the weight values for the selected track, and the small b button lets you edit the weight of the balance track.

Adding layer and transition tracks

If the Mixer button in the Biped Apps rollout is used to open the Motion Mixer, then the selected biped is automatically added as a track to the mixer interface. After the Motion Mixer is open, additional biped tracks may be added using the Add Biped button, which opens a dialog box listing the available bipeds in the scene.

Biped tracks added to the Motion Mixer include an additional balance track that isn't available for non-biped tracks.

Non-biped tracks are added using the Add Max Objects button on the toolbar. This button also opens a dialog box listing the available scene objects.

Additional tracks can be added to the interface using the Tracks Add Layer Track Above or the Tracks Add Layer Track Below menu commands. Transition tracks also are added to the interface using the Tracks menu. Transition tracks are taller than layer tracks and let you define the transition between overlapping clips.

Editing clips

Tracks can be trimmed easily from their original length by dragging on either end of the clip. The cursor changes when the cursor is positioned over the end of a clip. To see the clip's original size, click the Trim Clips button. The original clip size is shown in gray.

Editing track weights

Each track is associated with a weight value. The weight values define the influence of the track when two or more clips overlap. Weight values can range between 1.0 for full influence and 0.0 for no influence. If two overlapping clips both have a weight value of 1.0, then the topmost clip is used.

To edit a track weight, click the small w button to the right of the track. This enables the weight value, which appears as a red line for the track. If you position the cursor over the weight line, the cursor changes and lets you add an edit point if you click. This edit point may be selected and moved horizontally, vertically, or both horizontally and vertically depending on which button is selected on the right end of the toolbar. The weight value for the selected weight point is displayed in the value field to the right of the track. Several weight points may be selected and edited simultaneously.

Adding Time Warps

A Time Warp is just what it sounds like—a way to alter time or speed up and slow down animation clips. To add a Time Warp, select a clip and choose the Clips Add Time Warp. The cursor changes and lets you click the track to place the location of the Time Warp, which appears as a thin, vertical white line.

After a Time Warp has been added to a clip, you can enable Time Warp editing mode by clicking the Editable Time Warp button in the toolbar. A dashed line is overlaid on the clip. This dashed line gives you an idea of how the clip's time is being altered. Then click and drag the top of the Time Warp marker to crunch time in one direction, or click and drag the bottom half of the Time Warp marker to crunch time in another direction. The dashed lines show the relative effect. Figure 2 shows two layer tracks separated by a transition track. The top track shows the default spacing for a Time Warp, and the bottom track shows time compressed to the right.

FIGURE 2 Time Warps can be added to clips to compress time.

Working with Bipeds

The Motion Mixer also lets you work with biped objects. The combined animation results can then be copied and used on an existing biped to create new motions.

Copying mixed animation to a biped

After the mixed animation is complete, you can create a new track that includes all the mixed animation clips, called a Mixdown, using the Mix Compute Mixdown menu command. The Mixdown shows up as a new track and can be copied to a biped using the Mix Copy Mixdown to Biped menu command.

Saving and loading Mix files

All the clips loaded and edited in the Motion Mixer can be saved to an external file as a .mix file using the Mix Save Mix File and reloaded into the Motion Mixer using the Mix Load Mix File menu command.

Tutorial: Mixing biped animations

Mixing biped animations together can create some really interesting effects. For example, try mixing a back flip with a front flip, and you get a really dizzy biped, but for more common motions—such as a character transitioning from a walking animation to a fighting stance—the Motion Mixer can be extremely helpful and save you lots of time.

To mix two animation clips into a single motion, follow these steps:

1. Click the Systems icon in the Create panel, and select the Biped button. Then drag in the Left viewport to create a biped.
2. With the biped selected, open the Motion panel and click the Mixer button in the Biped Apps rollout to open the Motion Mixer. Notice that the Mixer Mode button in the Biped rollout is activated automatically.
3. Select the first biped track in the Motion Mixer by clicking its name, and choose the Tracks New Clips From Files menu command. In the Open dialog box that appears, locate and select the Walking.bip file from the CD. The animation clip is added to the Motion Mixer and is 78 frames long.
4. With the first track selected, choose the Tracks Add Layer Track Below menu command to create a new layer track.
5. Select the new layer track, and choose the Tracks New Clips From Files menu command again. In the Open dialog box that appears, locate and select the Fighting stance.bip file from the CD. This clip is only ten frames long.
6. Select the Walking track, and choose the Tracks Convert to Transition Track menu command. Then select and drag the Fighting stance clip to the bottom level of the transition track at frame 79. A transition between the two clips is added automatically, as shown in Figure 3.

   FIGURE 3 Two biped clips have been combined to produce a new animation.

   

7. Drag the Time Slider to see the resulting mixed animation. Then select the Biped root track, and choose the Mix Compute Mixdown menu command followed by the Mix Copy Mixdown to Biped menu command.

Summary

The Motion Mixer interface is used to combine multiple separate animation clips into a single smooth, new animation. Biped clips and animation clips for standard non-biped objects can be added and mixed in the Motion Mixer.

Specifically, this chapter covered the following topics:

• Using the Motion Mixer to edit tracks
• Adding transitions
• Adjusting weight values
• Mixing biped animations