HOWTO: Animate & Apply an Attraction Force to a Constraint
  
PSS ID Number: Q174415
Article last modified on 09-29-1997
 
IRIX:3.7; WINNT:3.7
 
IRIX winnt
 

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The information in this article applies to:
 
 - Softimage 3D for IRIX, version 3.7
 - Softimage 3D for Windows NT, version 3.7
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SUMMARY
=======
 
By default, when you apply a constraint to an object it sticks to the
object that you constrained it to. If your object is constrained to two
objects, the constrained object is positioned centrally between the two
objects by default.
 
The DopeSheet allows you to Activate/Deactivate a constraint, which causes
the constrained object to stick to the object that has the active
constraint. If both constraints are active at the same time, the
constrained object positions itself between the two.
 
In order to position the constrained object closer to one of the two
objects that it is constrained to, you must constrain it to a third object.
The location of the third object determines which of the two constraints
will have the most influence. This can be achieved by using the 3-point
constraint or by using three separate position constraints from the same
source to three different destinations, as detailed below.
 
MORE INFORMATION
================
 
1. Constrain a sphere to two nulls.
 
2. Select the constrained sphere and open the DopeSheet. The Object track
   that is displayed in the DopeSheet represents the constraint for the
   sphere.
 
3. Left-click in the gray box at the left of the green bar; CNSPOS appears,
   which represents the constraints.
 
4. To see all the constraint tracks, click a second time in the box where
   CNSPOS is indicated. The track expands, showing the two nulls to which
   the sphere is constrained.
 
5. The vertical tracks at the right of the green bars correspond to
   individual frames on your active timeline. All constraints are active by
   default. Therefore, to control the active state of your constraints over
   time, select a track area for the amount of time you want to deactivate
   your constraint.
 
6. Left-click on the track for Null1 and drag your mouse horizontally for
   the desired length of time. You can modify your selection on either side
   of the box afterwards. A white box appears which represents the selected
   frames.
 
7. To deactivate the constraint for the selected number of frames, click
   DEACT in the title bar of the DopeSheet window. The deactivated area
   should dim. The sphere's position constraint to null1 is active during
   the selected frames.
 
   You can use the same selection process for re-activating the constraint
   for any frame selection but click ACTIV.
 
8. To determine the frames where the sphere is not constrained to Null2,
   you must repeat the same procedure for Null1. If you do not offset your
   track selections between Null1 and Null2, both constraints will be
   deactivated at that time.
 
9. Add a position constraint to a third null. This null is used as the
   damping value for the constraint. Positioning the third null closer to
   one of the other two nulls recalculates the average point and as a
   result offsets your constraint.
 
10. To animate the force of the attraction that one constraint has over the
    other, animate the third constrained object in translation between the
    two master constraints.
 
REFERENCES
==========
 
If you have any questions concerning the information contained in this
article, contact support@softimage.com by e-mail.
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Keywords          : si si3d si3dconst
Version           : IRIX:3.7; WINNT:3.7
Platform          : IRIX winnt
Issue type        : kbhowto
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Copyright Microsoft Corporation 1997.