Cartoon Effects

This chapter describes how to stretch or scale bones to create cartoonish effects with skeletons in N-Dynamics.

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In this Chapter

• animate the lengthening of a bone (or bones) over the course of a script-a handy technique for creating some very "cartoonish" effects using the Skeletal Animation System

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Animating Changes in Bone Length

Suppose for example, that you want a character's arms or torso to change size over time. There are built in functions designed to animate just such an effect.

Note. If you animate changes in the length of bones that affect motion capture (e.g. the femurs in a walk cycle), you may throw off the motion capture.

To see such an animation:

1. Load the following script:

/usr/local/ngc/demo/scripts/lengthen-bone

There are four channels in the script:

• The Set View channel positions the camera

  
  

• The Read Acclaim Data channel reads in the motion capture data that we'll use to drive the skeleton

  
  

• The Scale Bone channel animates the change in lenght of a selected bone (this is the channel we're most interested in for this example).

  
  

• The Update Skeleton channel applies the motion capture data to the skeleton.

Notice that the Scale Bone channel is turned off when the script is read in; we'll turn it on after we've animated the script once so that you can see its effect.

The cat walks from left to right across the N-Geometry window.

Figure 9.1 Lengthen Bone operation properties

To animate the lengthening of a bone, you need to specify:

• The Skeleton that contains the bone to lengthen

  
  

• The Bone you want to lengthen. (You can (CLICK-L) on the bone in the N-Geometry window to see its name displayed in the upper left corner of that window).

  If you (CLICK-L) on the text edit box, a menu appears, showing all bones on the selected skeleton; (CLICK-L) on the bone you want to lengthen.

  
  
• The Lengthen mode:
  
  
  • Set uses the value in the curve channel underneath this operation as the absolute value of the bone.

    
    

  • Add adds the value in the curve channel to the bone's current length.

5. (CLICK-L) on the Lengthen Bone channel, then on the curve channel under it.

Note that we inserted a number of cues in the channel.

The cues represent the value used to lengthen the bone at that point in the script (using either the Set or Add mode described earlier).

(If you want to modify the values of the cues in the channel, you can either (SHIFT-L) on the cue itself, or (CLICK-R) on the curve channel and select the Edit all Cue Values operation.)

This makes the Lengthen Bone channel active.

This time the cat walks across the screen, but the torso bone stretches up and down to follow the cue values in the Lengthen Bone channel.

(It may be easier for you to see the actual change being made to the skeleton if you (CLICK-M) on the Update Skeleton channel and turn Skins>Update? to No.)

Of course, any skins attached to the bone stretch too; this is where you might want to create soft parts based on the change in a bone's length.

If you want to animate a change in a bone's scale (that is, specify a multiplier for the default bone length at each frame), you can do that too.

Try loading the following script:

/usr/local/ngc/demo/scripts/scale-bone

• Set and Add are the same as for Lengthen Bone
• Multiply uses the curve value as a multiplier-the current bone length is multiplied by the value in the curve channel

Note. If you use the multiply option, you should be careful when defining cue values-it's easy to specify a multiplier that would scale a bone to an amazing degree.

If you look at the cue values in the curve channel of the Scale Bone channel, you can see that some of the cues specify a value of 2.0, while others specify a value of 4.0; this is why the cat stretches more at certain points in the script than in others.

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Congratulations!

Copyright © 1996, Nichimen Graphics Corporation. All rights reserved.