Drivers

An AnimData block contains a list of all drivers as FCurves references. The driver contains a list of driver variables. Each variable contains a list of targets, which only contains more than one target if the type of the variable is "Rotational Difference" or "Distance". The target datablock references a data asset (like an object, scene, collection, bone...) and stores the data path as a string.

The driver also stores the expression as a string.

AnimData → Driver → DriverVariable → DriverTarget

Driver Variable Type

  • SINGLE_PROP Single Property – Use the value from some RNA property.
  • TRANSFORMS Transform Channel – Final transformation value of object or bone.
  • ROTATION_DIFF Rotational Difference – Use the angle between two bones.
  • LOC_DIFF Distance – Distance between two bones or objects.
  • CONTEXT_PROP Context Property – Use the value from some RNA property within the current evaluation context.

Driver Target

These are options for some important values:

rotation_mode

  • AUTO: Auto Euler. Euler using the rotation order of the target.
  • XYZ: Euler using the XYZ rotation order.
  • XZY: Euler using the XZY rotation order.
  • YXZ: Euler using the YXZ rotation order.
  • YZX: Euler using the YZX rotation order.
  • ZXY: Euler using the ZXY rotation order.
  • ZYX: Euler using the ZYX rotation order.
  • QUATERNION
  • SWING_TWIST_X: Swing and X Twist.
  • SWING_TWIST_Y: Swing and Y Twist.
  • SWING_TWIST_Z: Swing and Z Twist.

Decompose into a swing rotation to aim the axis, followed by twist around it.

transform_space

  • WORLD_SPACE Transforms include effects of parenting/restpose and constraints.
  • TRANSFORM_SPACE Transforms don’t include parenting/restpose or constraints.
  • LOCAL_SPACE Transforms include effects of constraints but not parenting/restpose.

Script Examples

To list all transformation drivers:

obj = bpy.context.active_object
for fc in obj.animation_data.drivers:
    print(f"- Driver of type \"{fc.driver.type}\": {fc.driver.expression}")
    for v in fc.driver.variables:
        print(f"-- Variable {v.name}")
        for t in v.targets:
            print(f"--- Target {t.id.name}: {t.data_path}")