Using the IK Toggle Switch

The most straightforward way of using IK on an hierarchy is to turn on the IK toggle switch and animate. If you try this on the model you just created, you will probably get some wild results, because we have not yet set any terminators or IK limits. Undo whatever changes you made, and let’s go fix those settings.

Setting a Terminator

To prevent the child from affecting the entire hierarchy, you need to set a terminator. A terminator is the lowest object in the hierarchy unaffected by movements of the end effector.

1.  Select the torso.

2.  Under the Hierarchy tab, select the IK button.

3.  Under the Object Parameters section, check Terminator.

4.  Now try moving the hand. This time, you can move the hand and the arm with it, without the whole body going all over the place.

Setting IK Limits

Setting IK limits can be laborious. In our example, if we wanted to use IK, we should have set the IK limits of the left arm before mirroring it, because the Mirror tool has an option of mirroring the IK limits. Let’s not worry about that, and just set some limits for the left arm.

1.  Select “arm upper L.”

2.  In the IK part of the Hierarchy tab, open up the Rotation Joints rollout.

3.  Check Active and Limited for all the axes.

4.  Drag the From and To spinners for the X axis up and down and watch the display in the viewport. Use these spinners to set the range of motion you want for this joint around this axis.

5.  Drag the From and To spinners for the Y axis to set the range of motion you want around the Y axis.

6.  Drag the From and To spinners for the Z axis to set the range of motion you want around the Z axis.

7.  Select “arm lower L” and use the From and To spinners to set limits for the rotations around X and Y. Uncheck Active for the Z axis, since the arm can’t rotate in that direction at that joint.

8.  Select “hand L” and use the From and To spinners to set limits for the rotations around X and Y. Uncheck Active for the Z axis.

9. Click the IK Toggle button.

10.  In case you want to do this over, save the file as hierarchy_IKlimits.max. You can also view this file on the CD.

11.  Go to frame 100 and turn on the Animate button.

12.  Move the hand to a position in front of the torso.

13.  Turn off the Animate button and play the animation.

14.  Save As hierarchy_ik1.max.

Using Follow Objects

Another type of IK in MAX involves using a follow object, often a dummy object, to calculate IK for a certain range of frames. In our example, instead of animating the hand, you would animate a dummy moving from one hand position to another. You would then go to the IK part of the Hierarchy tab and bind the hand to the dummy follow object by clicking Bind and dragging from the hand to the dummy. Then you would click the Applied IK button for the range of the animation. The resulting calculation of the IK is different from using the toggle switch.

You can check out the difference between equivalent IK animations in files hierarchy_ik1.max (the same one you created in the above exercise, with the IK toggle switch) and hierarchy_ik2.max (created with applied IK), both of which are included in the CD for this book.

	TIP To get the IK results you want more precisely, adjust the thresholds under Customize Ø Preferences Ø Inverse Kinematics.

Animating with Bones

MAX Bones is a hierarchical system of non-renderable objects with a special IK controller assigned. In this case, the IK Toggle switch and follow objects are unnecessary, because the IK solution is automatically calculated. Bones can be used to deform either a segmented hierarchy or a single mesh. They can also be added to a Character Studio biped when needed. Bones are created from the Systems section of the Create tab. Let’s look at an example, applying Bones to our hierarchical model.

1.  If you used the Hold command earlier, when we built the body hierarchy, use Edit Ø Fetch to bring back the model unanimated. Or, open the file hierarchy_unanimated.max from the CD.

2.  Go to Create Ø Systems Ø Bones.

3.  Under the Auto Boning section, make sure Auto Link is checked and click the Pick Root button.

4.  Click the torso. Voila! A whole IK skeleton is created.

5.  Click the Move tool to get out of creating Bones.

6.  To animate, you need to make sure you select a Bone rather than the model. The best way is to use the Select by Name dialog box to select the Bone you want. Select Bone07, which is above the hand in the hierarchy.

7.  Lock your selection.

8.  Go to frame 100 and turn on the Animate button.

9.  Move the hand Bone to where you want it.

10.  Turn off the Animate button and play the animation.

	NOTE You can see an example of this exercise in the hierarchy_bones.max file that comes with the CD.

Using Bones to Deform a Single Mesh Until MAX R3, Linked XForm was the only way to use MAX Bones to deform a single mesh. For deformation with envelope control, you had to use a third-party plug-in like Bones Pro or Character Studio’s Physique. In MAX R3, we now have the Skin modifier. Often described as a “light” version of Physique, Skin allows you to deform a single mesh skin according to envelopes assigned to bones, whether MAX Bones or other objects used as bones.

To deform a single mesh, you would make your skeleton and apply the Skin modifier to the mesh. In the Modify tab of Skin, you would add the bones: a hierarchy of MAX Bones or of ordinary boxes. You would then go to the Envelope sub-object level of each bone and adjust it to affect the area of the mesh you want it to deform.

	NOTE In addition to the Skin modifier, Bones can be used with Digimation’s Bones Pro and Character Studio’s Physique modifier.

Working in Character Studio

Up until now, we have not dwelt on any of the many powerful plug-ins available for MAX. Of these, the most essential for character animation is Character Studio. Character Studio 2.2 ships with MAX R3; you will receive an authorization code for it when you purchase the program. Character Studio is the most common way of animating hierarchical characters in MAX. It is a challenge to master: we will discuss the basic elements of the Character Studio program to get you started.

Character Studio consists of two plug-ins: the Biped system, available under Systems in the Create tab; and the Physique modifier. Let’s get an overview of each of these plug-ins.

© 2000, Frol (selection, edition, publication)