Tangent options

By default, MotionBuilder automatically manages the slope, or interpolation, of function curves. The three Tangent options (Auto, Linear, and Stepped) let you select how MotionBuilder interpolates the values between keyframes in order to manually change the interpolation.

NoteTurning on Classic Mode from the FCurves contextual menu will display the classic toolbar and all five (Auto, TCB, Stepped, Linear, and Fixed) tangent options.

Tangent options in the FCurves window A. Auto B. Linear C. Stepped

To change interpolation, select one or more keyframes, then select an interpolation option. Depending on the option you choose, the interpolation between the selected keyframes changes.

When you change the interpolation of a keyframe region, you affect the shape of the curve between the keys in the region and the next set of keys that follow the region.

For information on changing the mathematical algorithm that calculates the extrapolation of a curve, see Extrapolation.

Auto option

Activates Auto interpolation mode. The tangents of an Auto key type will automatically be adjusted based upon the interpolation of the previous and next keys. How this tangent will be affected is based upon one of the Auto types, which can be adjusted in the FCurve Preferences window.

Auto tangent default types in the Preferences window

The following table describes the Progressive Clamp, Spline, and Smooth default types that are available when you select Auto interpolation mode.

Auto tangent default type	Description
Progressive Clamp	This is the default Auto type. As an all-encompassing Auto key type, Progressive Clamp is a combination of spline, clamp, and flat behavior. Auto keys of this type have the following characteristics: Time independent Clamp with ease-in and ease-out behavior Flat overshooting and undershooting interpolation
Spline	Auto keys of this type have the following characteristics: Time independent Clamp (optional)
Smooth	Auto keys of this type have the following characteristics: Time dependent Clamp (optional)

There are two options in the FCurves contextual menu that affect your use of Auto and Fixed modes. See Switch to User on Edit and Reset Tangents on Switch to Auto for more information.

TCB option

Activates TCB interpolation mode, joining each keyframe using a Hermite-type curve. The slope on either side of a keyframe is changed using the TCB (Tension/Continuity/Bias) values.

Stepped option

Activates Stepped interpolation mode, maintaining the same keyframe value between keyframes. With Stepped interpolation mode active, there is no slope between keyframes. This option replaces the behavior of Constant in previous versions of MotionBuilder.

While working in Classic Mode, clicking the Stepped option on the FCurves window toolbar will make the Step Normal and Step Next options appear (B and C in the figure).

Tangent options A. Stepped option is active B. Step option C. Step Next option

Step option

When the Step option is active, Stepped interpolation maintains the value of the selected keyframe until the next keyframe.

Step interpolation A. Selected keyframe B. Next keyframe

Step Next option

When the Step Next option is active, Stepped interpolation maintains the value of the next keyframe between the selected and next keyframes.

Step Next interpolation A. Selected keyframe B. Next keyframe

Tip

The Step Next interpolation is useful for marking the end of a referential when using the Multi-Referential constraint.

Linear (Lin) option

Activates Linear interpolation mode, joining the selected keyframe and the next keyframe with a straight line. The slope between keyframes while this mode is active is constant.

Fixed option

Fixed interpolation produces a cubic curve whose slopes are not influenced by neighboring keyframes. When you edit neighboring keyframes, the tangents of a Fixed keyframe do not change. In Fixed mode, moving one tangent handle moves the other tangent equally.