Setting
up the FK/IK Blend
The ability to blend between FK and IK is a default behaviour of
the Inverse Kinematics setup in Houdini. You can access the blend
attribute using the following method:
1.
Create and Pose an IK setup
Select tab
> Character Bones, place two bones into front
view then RMB-click
to accept. Select tab > Character
> Pose, click on one of the bones then RMB-click
to accept. You can now move the end effector to move the end of
the chain. Press r
to get the rotation handles on the bones. Because Inverse Kinematics
is controlling the chain, rotations do not work.

2.
Adjust the Blend Handle
RMB-click
on the end effector handle and select Show
Blend Handle. A new handle shows up at the bottom
of the chain's axis line. Drag this handle up until it is closer
to the root of the chain. The blend parameter value becomes visible
as you drag and gets set to 0 at the root.

Now you can
use the rotation handles on the joints to pose the bones. 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, the parameter is updated on the channel
operator.
3.
Snapping between setups
Press t
to go back to the end effector translate handle. You can see that
the end effector has been rotated along with the bones. This is
because of the Auto-snap IK/Rotates option on the handle. You can
choose to turn this off by RMB-clicking on the handle and selecting
Auto-snap IK/Rotates.
Move the handle to confirm that the end effector no longer affects
the chain.

When the end
effector and the joint rotations have been manipulated separately,
you can get them back together by RMB-clicking
on the handle and selecting either Snap
to IK or Snap
to Rotates. Setting the Blend
parameter back to 1
is another way of smoothly blend the rotated joints back to the
end effector.
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