Blender Documentation: Last modified September 29 2003 S68 | ||
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Constraints are filters that are applied to the transformations of bones and objects. This section is actually quite general and does not apply only to character animation since many other animations can benefit from constrains.
Blender Constraints can provide a variety of services including tracking and IK solving.
To add a constraint to an object, ensure you are in object Mode and that the object is selected. If you are adding a Constraint to a Bone be sure to be in Pose Mode and select the Bone. Switch to the constraint Buttons Window (the icon looks like a pair of chain links - (Figure 17). and click on the Add button.
A new constraint will appear. It can be deleted by clicking on the "X" icon next to it. A constraint can be collapsed by clicking on its orange triangle icon. When collapsed, a constraint can be moved up or down in the constraint list by clicking on it at choosing Move Up or Move Down from the popup menu.
For most constraints, a target must be specified in the appropriate field. In this field you must type in the name of the desired target object. If the desired target is a bone, first type in the name of the bone's armature. Another box will appear allowing you to specify the name of the bone.
Several Constrains are possible. All applies to Bones, some applies Also to other Objects:
IK Solver (Bone Only) - To simplify animation of multi-segmented limbs (such as arms and legs) you can add an IK solver constraint. IK constraints can only be added to bones. Once a target is specified, the solver will attempt to move the root of the constraint-owning bone to the target, by re-orienting the bone's parents (but it will not move the root of the chain). If a solution is not possible, the solver will attempt to get as close as possible. Note that this constraint will override the orientations on any of the IK bone's parents (Figure 18).
Copy Rotation - This constraint copies the global transformation of the target and applies it to the constraint owner (Figure 19).
Copy Location - The constraint copies one or more axes of location from the target to the constraint owner (Figure 20).
Track To - This constraint causes the constraint owner to point its Y-axis towards the target. The Z-axis will be oriented according to the setting in the Animation Buttons Window. By default, the Z-axis will be rolled to point upwards (Figure 21).
Action (Bone Only) - An Action constraint can be used to apply an Action channel from a different Action to a bone, based on the rotation of another bone or object. The typical way to use this is to make a muscle bone bulge as a joint is rotated. This constraint should be applied to the bone that will actually do the bulging; the target should point to the joint that is being rotated (Figure 22).
The AC field contains the name of the Action that contains the flexing animation. The only channel that is required in this Action is the one that contains the bulge animation for the bone that owns this constraint
The Start and End fields specify the range of motion from the Action.
The Min and Max fields specify the range of rotation from the target bone. The Action between the start and end fields is mapped to this rotation (so if the bone rotation is at the Min point, the Pose specified at Start will be applied to the bone). Note that the Min field may be higher than the Max.
The pulldown menu specifies which component of the rotation to focus on.
Null - This is a constraint that does nothing at all; it doesn't affect the object's transformation directly. The purpose of a null constraint is to use it as a separator, and why this might be necessary will be clarified in the following section (Figure 23).
Constraints can be applied to objects or bones. In the case of constraints applied to bones, any constraints on the armature object will be evaluated before the constraints on the bones are considered.
When a specific constraint is evaluated, all of its dependencies will have already been evaluated and will be in their final orientation/positions. Examples of dependencies are the object's parent, its parent's parents (if any) and the hierarchies of any targets specified in the constraint.
Within a given object, constraints are executed from top to bottom. Constraints that occur lower in the list may override the effects of constraints higher in the list. Each constraint receives as input the results of the previous constraint. The input to the first constraint in the list is the output of the IPOs associated with the object.
If several constraints of the same type are specified in a contiguous block, the constraint will be evaluated once for the entire block, using an average of all the targets. In this way you can constrain an object to track to the point between two other objects, for example. You can use a Null constraint to insert a break in a constraint block if you would prefer each constraint to be evaluated individually.
Looping constraints are not allowed. If a loop is detected, all of the constraints involved will be temporarily disabled (and highlighted in red). Once the conflict has been resolved, the constraints will automatically re-activate.
The influence slider next to each constraint is used to determine how much effect the constraint has on the transformation of the object.
If there is only a single constraint in a block (a block is a series of constraints of the same type which directly follow one another), an influence value of 0.0 means the constraint has no effect on the object. An influence of 1.0 means the constraint has full effect.
If there are several constraints in a block, the influence values are used as ratios. So in this case if there are two constraints, A and B, each with an influence of 0.1, the resulting target will be in the centre of the two target objects (a ratio of 0.1:0.1 or 1:1 or 50% for each target).
Influence can be controlled with an IPO. To add a constraint IPO for a constraint, open an IPO Window and change its type to constraint by clicking on the chain icon. Next click on the Edit IPO Button next to the constraint you wish to work with. If there is no constraint IPO associated with the constraint yet, one will be created. Otherwise the previously assigned IPO will be displayed. At the moment, KeyFrames for constraint IPOs can only be created and edited in the IPO Window, by selecting the INF channel and CTRL-LEFTMOUSE in the IPO space.
When blending Actions with constraint IPOs, note that only the IPOs on the armature's local Action IPOs are considered. Constraint IPOs on the Actions in the motion strips are ignored.
![]() | In the case of armatures, the constraints IPOs are stored in the current Action. This means that changing the Action will change the constraint IPOs as well. |
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