Roll

...rotates an object depending on its global position change; in other words: lets an object roll ;)

Active Initialization Radius Roll-Axis Attributes

Active & Active while Editing

Like every part, you can activate or deactivate ROLL using "Active". The two other parts are not affected.
The expression influences alle interactions in the viewport: if you simply move an object there, it already "rolls". If "Active while Editing" is deactivated, this interaction is prevented and only the animated/keyed position changes are interpreted by ROLL. You need this for, e.g. setting a new initialization position without rotating the object.
Summary: When "Active while Editing" is deactivated, the object will only roll while playing and rendering the animation.
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Initialization

Every Roll-It tag has got an initialization position and rotation. On frame 0, the object is repostioned to this starting position and rotation.
The initialization is local, that means, if the object is placed inside a hierarchy, and the hierarchy is moved to another position, the initialization position moves, too.
When you create the Roll-It tag, the current local position and rotation is set as initialization point. If necessary, a new starting position/rotation has to be set using, of course, the "Set" button ;)
With "Show", the object is relocated to the current initialization point, or rather, the position is shown in the viewport.
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Radius

What counts for the "rotation speed", is the object's radius. While creating the expression tag, Roll-It tries to calculate the object's radius and puts it under "Radius" in the Roll-tab. The radius complies with one half of the object's local y-size. For some objects, Roll-It is not able to calculate the radius, e.g. Nurbs objects. In this case, the radius is set to "1" and you need to set the radius manually (note: a radius smaller or equal to null is not allowed.)

Optionally to the "local bounding box", the radius resulting from half-height can be calculated using a "global bounding box". This method, in combination with "Calculate per Frame" is useful for objects that have a changing radius during rotation, e.g. a cube.
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Roll-Axis

With using Roll-Axis, you can limit the rotation to axis P or B. This makes sense, e.g. for a tire, that, unlike a sphere, only needs to rotate in one axis. The roll axes are local.
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Attributes

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