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Chapter 22: Animating with Constraints and Simple Controllers

Tutorial: Attaching eyes to a melting snowman
When part of a model is deformed, such as applying the Melt modifier to a snowman’s body, smaller parts
like the eyes either get left behind or get the full weight of the modifier applied to them. If the Melt modifier
weren’t applied to these items, they would stay floating in the air while the rest of the snowman melted
about them. This problem can be fixed with the Attachment constraint, which causes the eyes to remain
attached to the snowball as it melts.
Cross-Ref
The tutorial where the Melt modifier is applied to the snowman is included in Chapter 34, “Using Animation
Layers, Modifiers, and Complex Controllers.” n
To constrain the solid objects to a melting snowman, follow these steps:
1. Open the Melting snowman.max file from the Chap 22 directory on the DVD.
This file includes the melting snowman file from the previous chapter with the Melt modifier
applied to all objects.
2. Select the left eye object in the scene. In the Modifier Stack, select the Melt modifier and click the
Remove Modifier button to throw that modifier away.
3. With the left eye still selected, select Animation ➪ Constraints ➪ Attachment Constraint. A connect-
ing line appears in the active viewport. Click the top snowball to select it as the attachment object.
This moves the eye object to the top of the snowball where the snowball’s first face is located.
4. In the Attachment Parameters rollout, change the Face value until the eye is positioned where it
should be. This should be around face 315. Then change the A and B values (or drag in the
Position graph) to position the eye where it looks good.
5. Repeat Step 5 for the right eye and for any other objects in the scene that you want to attach.
6. Click the Play button (/) and notice that the snow melts, but the eye objects stay the same size.
Figure 22.1 shows the resulting melted snowman.

Surface constraint
The Surface constraint moves an object so that it is on the surface of another object. The object with Surface
constraint applied to it is positioned so that its pivot point is on the surface of the target object. You can use
this constraint only on certain objects, including Spheres, Cones, Cylinders, Toruses, Quad Patches, Loft
objects, and NURBS objects.

Caution
Because the Surface Constraint works using the parametric nature of the attached surface, only certain object
types can be used with the surface constraint, including primitive objects like a sphere, cone, cylinder, patch, and
NURBS objects. n
In the Surface Controller Parameters rollout is the name of the target object that was selected after the menu
command. The Pick Surface button enables you to select a different surface to attach to. You also can select
specific U and V Position values. Alignment options include No Alignment, Align to U, Align to V, and a
Flip toggle.

Note
Don’t be confused because the rollout is named Surface Controller Parameters instead of Surface Constraint
Parameters. The developers at Autodesk must have missed this one. n

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