Building Repetitive Motion with Trax

Maya offers an innovative solution to character animation called Trax, which allows you to simplify repetitive motions and build libraries of movements. Trax is Maya's version of what is known as "non-linear animation." Non-linear animation mimics the approach taken by computer-based video editors, where a timeline is displayed and footage appears as bars that can be placed, moved, copied , and layered across this timeline to compose a TV program.

With Trax, if you have a character animated to applaud, you can save this bit of animation as a clip. Then, any time the character should applaud , you simply layer this clip over the other animation that is already applied to this character. Regardless of whether the character is running, hopping , or standing still, the hands will clap where specified.

An additional method of using Trax involves poses. Here, instead of using collections of animation, you simply use still poses and blend them in as desired. You can blend any set of poses or animations in Trax. Your library of poses and animation clips reside in Visor.

Tutorial: Repeating the Walk Using Trax

Now that the character takes a single step between frames 30 and 60, we could just repeat these steps in Maya to make him walk a few more strides. But that would be mindless and boring. Instead, let's look at the Trax Editor, a way to use animation "clips" to create repetitive motion in Maya.

1. Select the ring handles for the hands, feet, and waist. Choose Hotbox Animate Create Clip option box. Reset the dialog and change the name to one_step; then change the time range to Start/End, set the start time to 30, and set the end time to 60. Uncheck sub- characters and click the Create Clip button, as shown in Figure 11.20.

   

   Figure 11.20. Creating a clip of a single walk cycle.

   

2. Open the Trax Editor with Hotbox Window Animation Editors Trax Editor. You'll see the clip you created here. When you created the clip, it also created something called a character setthis is required of anything that Trax will work on. A character set is a group of related objects that are to be animated togetherusually a character and its skeleton, IK handles, and other related nodes. The automatically created character set in this tutorial is given the default name of "MultiCh."

3. If you scrub time, you'll notice that animation now exists only for the character for frames 30-60. By creating a character set and a Trax clip, all the character's animation is now moved to the Trax clip.

4. In the Trax Editor, click the second button from rightthe frame timeline range button. Now you can see the clip in context of all 120 frames. Click on the clip and drag it to frame 1. Now play back the animation, and you'll see the one walk cycle begin at frame 1.

5. Next, right click in the space to the right of the animation clip in Trax. Choose Library Insert Clip one_stepSource, as shown in Figure 11.21. A new clip, a copy of the original named one_step1, will appear below the original in the Trax Editor. Drag the clip to the right side of the original clip and make it start at frame 31 so that the ends of the clips touch. Drag the animation, and you'll see the walk happen twice in a rowbut restarting from the same position each time!

   Figure 11.21. The motion clip you created is now in the clip library, and right-clicking in the Trax Editor allows you to easily insert the animation.

   

6. Right-click the new clip and check the relative clip box. Now play back the animation, and you'll see the walk continue as you would want. Insert two more copies of one_stepSource as in Step 4, and set these new clips to Relative mode as well. Now play back the animation, and you'll see 120 frames of walking.

7. If you'd like to see a higher-resolution BoxBoy, apply a smooth to the character by selecting the mesh and choosing Hotbox Polygons Smooth. In the Channel Box, click the PolySmoothFace entry and scroll to the bottom of the Channel Box. Here you can adjust the number of divisions, as shown in Figure 11.22. Set this to 1 so the animation will play back fairly fast.

   Figure 11.22. Adjusting smoothing on the character.

   

At this point, you can render a playblast or a full movie of the character walking. As you might surmise, you could now create libraries of other motions and mix them in using Trax to make very complicated animation. But so far, we've only touched on the methods Maya uses for character body motion. Next, we'll turn to facial animation, where characters can really come alive .