INSIDE 3DS MAX® 7 [Electronic resources] نسخه متنی

Biped Animation Basics

Characters don't just sit or stand aroundthey walk, run, leap, and dance. These motions can be quite hard to get right, especial for newer animators. Luckily, character studio has special features to make locomotion much easier.

Free Form and Footstep Animation

There are two types of animation you can do with Biped: Free Form animation and Footstep animation. With Free Form animation, Biped is like a completely ready-to-animate rig. Free Form animation is done with simple keys using IK (inverse kinematics) and FK (forward kinematics) and includes very powerful pivot animation on the hands and feet. You can animate the pivot point from one position to another on the extremities to easily lock the feet down to the ground plane.

Footstep animation lets you create basic footsteps for the Biped to follow. It's a fast way to rough out animation that can then be refined. It lets almost anyone create walking characters without having to know how to animate a walk cycle.

Quaternions

character studio uses quaternion controllers to position and rotate parts of the Biped. (Quaternions are based on an alternate way of figuring rotations that takes into account a fourth, non-Cartesian axis of rotation.) Quaternions and TCB controllers have their advantages and disadvantages. Quaternions can produce smoother animation and help avoid the dreaded gimbal lock, but it can be hard to edit the interpolation between keyframes. This is because quaternions don't produce curves for editing. To edit the interpolation between quaternion keys, you must use a TCB graph.

When editing in the TCB graph, you can adjust the tension, bias, and continuity. In the most recent release of cs, you are now able to visualize and edit quaternion keys with curves in the Animation Workbench editor. The Workbench allows you to view and edit quaternion values in curve form (Figure 15.11).

For years there has been controversy over the issue of function curves inside character studio. Most animators adept with other software packages such as Maya or Softimage are used to using tangent handles on the curves to achieve their motion adjustments. Since character studio is built on TCB controllers, these curves were not available in earlier releases.

You can turn on tangent handles on the TCB curves by changing a setting in the BIPED.INI file in the plucfg folder. To do so, open the BIPED.INI file in Notepad, and edit it so this line appears:

AWB_ShowTangents=1

Restart max and you will have tangent handles on your TCB curves (Figure 15.12). Be forewarned, however, that these do not act the same as normal tangent handles on Euler curves. They are simply a device to adjust the tension, continuity, and bias. Most animators trained in 3ds max find it just as easy to right-click the keys and work with the TCB graphs.

Setting Keys

There are many ways to set keys with character studio. To rough out your animation, you can use Auto Key mode to move and rotate the Biped into place. Biped switches automatically between IK and FK depending on what part of the rig you have selected and if you are moving or rotating it. When moving either the hands or the feet, you will be using IK. If you rotate the feet or part of the spine, you will be using FK. This ease of use is one of the great things about animating with character studio. When creating keys, you will want to decide whether the key is an IK or FK key. You can do this by setting two values, IK Blend and Object/Body space, in the Key Info rollout (Figure 15.13).

When IK Blend is set to 1 and Object is selected, the key is an IK key, and when the body is moved, the hand or foot will stay in place. When IK Blend is set to 0 and Body is selected, the key will be FK and the foot or hand will follow with the body. IK Blend can be animated from 0 to 1 to smoothly transition between IK and FK movement.

One other option that is very useful when setting keys is Join to Prev IK Key. This function determines if the key should be part of (blended with) the previous key (and have the same reference position as the previous key). This option can be checked to prevent sliding of a foot or hand from one key to another.

Setting all these values for keys can be maddening, so there are shortcuts you can use. The buttons at the top of the Key Info rollout set all these values according to how you would like the key to react.

• Set Planted Key sets IK Blend to 1, turns on Join to Prev IK Key, and uses Object space. Using Set Planted Key lets you select and lock down the pivot point on the hands and feet.

• Set Sliding Key turns off Join to Prev IK Key, but IK Blend is still set to 1 and Object space is selected. Set Sliding Key lets the foot slide away from the pivot point.

• Set Free Key turns off IK Blend and Join to Prev IK Key and uses Body space.

Using these presets can save a lot of time and energy. It can make animating more about the movement. Is the foot to be locked to the ground? Use Set Planted Key. Is the foot going to be in the air? Set Free Key. It's simple, really.

When Object space is used on the hands or feet, you can select an object in the scene and lock the hand or foot to the object. Moving the object will force the rotations of the limbs between the locked object and the Biped body. Unfortunately, you must choose one object only; you cannot animate the contents of the Object space field. You can, however, animate one object between the two hands.

Tip

Never use the 3ds max Set Keys button to set character studio keys. Biped has its own key-setting system, and it doesn't like it when you use the default 3ds max Set Keys feature instead. The same caveat applies to Trajectories. In the past, using 3ds max Trajectories on Bipeds would produce a crash. Use Biped Trajectories instead.