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Blend between IK and rotations

When you animate a bone chain you sometimes want to use bone rotations to drive the motion while other times you want to use an IK goal.

Houdini’s IK set-up lets you smoothly transition between the two control schemes with a blend attribute you can set with an interactive handle in the Pose tool.

Tip

The blend handle and Snap to IK/Rotates menu items mentioned below are available when using the default, single goal setup. If you change the default setup to blend between multiple goals, these UI convenience features will not work. See two approaches to rigging for details.

To...Do this

Blend/switch between IK and rotations

  1. Use the tab menu to choose the Pose tool.

  2. Click an IK bone chain. The goal lets you move the end of the chain. Press R to show rotation manipulators for the bones. Because the IK solver is controlling the chain, the rotation handles have no effect.

  3. In the operation control toolbar at the top of the viewer, make sure Handle Mode is set to Object specific handles.

  4. Select the last bone.

  5. Press RMB on the goal handle and choose Show Blend Handle.

    A new handle appears at the bottom of the chain’s axis line.

  6. Drag the blend handle back along its slider line. The closer it is to the root end of the line, the more joint rotations affect the chain.

  7. You can now select joints and use the rotate manipulator (R) to rotate them.

    The rotations are proportionally modified by the blend handle. Large rotations will have a small effect if the blend factor is low. If you then go back and turn up the blend factor, the effect of the rotation will magnified.

Reset the bones to match the IK or rotations

  1. Use the tab menu to choose the Pose tool.

  2. Select the last bone.

  3. Press RMB on the goal handle and choose Snap to IK or Snap to Rotations.

Keyframe IK/rotation blending setups

Note

The blend parameter is part of the kinematics channel operation (kin_chop) that is driving the Inverse Kinematics solution. When you adjust this value using the handle, Houdini updates the parameter on the channel operator.