In this example, we add FK rig logic to a 3-joint tube geometry using the FK transform rig component:

1. We start by drawing a skeleton for the tube geometry (see working with skeletons for more information on creating skeletons.):

   

   • On the Tube SOP, set Rows to 3 and adjust the other parameters to change the size of the tube.

   • Draw a skeleton with 3 joints - point_0, point_1, and point_2 - where point_0 is the parent of point_1, which is the parent of point_2.

     

2. Connect the network below, which adds FK rig logic to the character (in this example, we don’t add bone deformation to the rig logic, so the tube geometry is no longer needed):

   

3. The Pack Folder SOP adds the tube skeleton to a packed character folder structure. We name this skeleton tube.skel - on the Pack Folder SOP, set Name to tube and Type to skel.

4. See the contents of the packed character folder structure in the rig tree view:

   • Select the Pack Folder SOP in the network editor.

   • At the top of a pane, click the New Tab icon and select New Pane Tab Type ▸ Animation ▸ Rig Tree.

   • In the rig tree view, beside the node name (in our case, add_to_packed_folder), set the drop-down box to the output.

   • Set Type to Packed Folders. The following packed folder structure is displayed:

     /
     -- tube.skel
     

5. On the APEX AutoRig Component SOP, set the Component Source parameter to FK Transform. This FK rig component creates a rig graph by translating the tube skeleton into a rig hierarchy; it takes each of the skeleton joints and creates a TransformObject node in the rig graph. The TransformObject nodes can then be turned into controls that the user can interact with in the animate state.

   By default, the FK component adds the tag “bind” to all the TransformObject nodes it creates. This tag is specified in the Tags parameter. The bind tag is then picked up by other rig components downstream to add functionality to all the “joints” (TransformObject nodes) in the rig.

   Tip

   Because the FK component translates a skeleton into a rig hierarchy, it is useful to have this as the first prebuilt component when building a rig for a character.

   Note

   By default, the rig that is created by the FK component is named Base.rig (Rig section, Name parameter). You can change the name of the rig, but be aware that all the other prebuilt rig components also have their default rig name set to Base.rig, so you would have to update all the rig names down the chain of APEX AutoRig Component SOPs in your network.

6. We don’t have a guide skeleton, so set Guide Source to tube.skel.

7. In the Settings tab, Output Skeleton parameter, specify the skeleton to output, in our example, tube.skel.

8. In the Source tab, Skeleton parameter, specify the skeleton to use to create the rig hierarchy, in our example, tube.skel.

9. To create controls on the rig, populate the Promote* parameters in the Controls tab with the TransformObject nodes you want to turn into controls. You can use the APEX path pattern syntax to specify groups of TransformObject nodes. In our example, we want to promote the translation and rotation for all our controls, so we set Promote T and Promote R to *.

10. The FK component adds the rig graph to the packed character folder structure, as seen in the rig tree view:

    /
    -- Base.rig
    -- tube.skel
    

    In the APEX network view, we can see the rig graph generated by the FK component, as shown below (nodes are rearranged and colors are added for clarity). The TransformObject nodes represent the skeleton joints, and are connected according to the skeleton joint hierarchy. The translate and rotate of each TransformObject node are promoted:

    

    See geometry deformation for more information on the TransformObject and skel::SetPointTransforms nodes.

11. View the FK functionality in the animate state:

    • Select the APEX AutoRig Component SOP and turn on its display flag.

    • Click Animate on the left toolbar or press Enter in the viewport.

We now add bone deform logic to the FK rig graph using the bone deform rig component. To perform bone deformation, we first need to create capture weights on the geometry using the Joint Capture Biharmonic SOP. We then add the updated geometry to the packed character folder structure along with the skeleton:

In other DCCs, weight creation often happens on the deformer. In Houdini, weight creation is separate from deformation, so we can prepare the input geometry with the correct weights before diving into APEX to create the rig logic.

1. The Pack Folder SOP adds the tube geometry and skeleton to a packed character folder structure:

   • The first input to the Pack Folder SOP is the tube geometry used for the deformation. We name this geometry tube.shp (set Name to tube and Type to shp).

   • The second input is the tube skeleton. We name this skeleton tube.skel (set Name to tube and Type to skel).

   Note

   The order of the inputs to the Pack Folder SOP must match the order of the Name and Type parameters in the Pack Folder SOP. See assembling animation data for more information on naming character elements in the packed character folder structure.

   We can see the following packed folder structure in the rig tree view:

   /
   -- tube.shp
   -- tube.skel
   

2. The APEX AutoRig Component SOP, bonedeform, adds bone deformation logic to the rig graph created by the FK component upstream. On the bonedeform node, set Component Source to Bone Deform. By default, the bone deform component adds logic to Base.rig (set in the Rig section, Name parameter).

3. In the Settings tab, change the following parameters to match the names of the geometry and skeleton in the packed character folder structure:

   • Rest Geo = tube.shp. This is the geometry with the capture weights we want to deform.

   • Rest Skeleton = tube.skel. This is the name of the input skeleton that is the base for the capture weights. The joints of Rest Skeleton need to match up with the capture weights on Rest Geo.

   • Output Geo = tube.shp. This is the name of the output geometry we want to display. It is usually the same as Rest Geo.

4. View the additional logic that the bone deform component has added to the FK rig graph (added bone deform logic is in purple):

   

5. View the bone deformation in the animate state:

In this example, we start with the FK rig from the previous example and add IK functionality using the multi IK rig component:

1. We only want to manipulate the IK controls, so we don’t need to promote the FK joints to be controls. On the fk node, remove all the TransformObject nodes from the Promote* parameters in the Controls tab.

2. On the APEX AutoRig Component SOP, ik, set the Component Source parameter to Multi IK.

3. Set Guide Source to the skeleton in the packed character folder structure, tube.skel.

4. In the Driven tab, set Segments to bind. You could also choose bind from the drop-down menu. bind is a tag that was previously added to the TransformObject nodes created by the FK transform rig component. By specifying bind in the Segments parameter, the multi IK component picks up the appropriate TransformObject nodes in the rig hierarchy and adds IK functionality to it.

5. View the IK functionality in the animate state:

The transform driver rig component is used to create new controls that drive the transforms (translate, rotate, and scale) of existing controls in the skeleton - the existing controls are essentially constrained to the new controls. The transform driver component allows you to define different pivots and orientations for the existing joints without having to create new skeleton controls that would otherwise affect any bone deformation downstream.

In an APEX graph, the transform driver component creates new TransformObject nodes and adds a constraint between the new and existing nodes. The new nodes are not added to the skeleton; they are just extra controls used to drive the skeleton joints.

In this example, we add new controls to the FK rig from the previous example:

1. On the APEX AutoRig Component SOP, transformdriver, set the Component Source parameter to Transform Driver.

2. Set guidesource to the skeleton in the packed character folder structure, tube.skel.

3. We add a transform driver control, root, that sits at the position of point_0 and drives the translation and rotation of point_0:

   • In the Settings tab, turn on use_t, use_r, and use_s.

   • In the Driven tab, set driventransforms to point_0. This is the joint that is driven by the control.

   • In the Control tab, driver parameter, specify a name for the new control. We set driver to root.

   • Set driverguide to point_0. This is the position of the new root control. (The restlocal parameters for the new root TransformObject node will be set to the position of point_0.) If nothing is set in driverguide, the new control is created at the origin.

   • Specify the transform components that are driven by the control - turn on makecontrol, promotet (translate), and promoter (rotate).

   • Configure the control shape in the Shape tab.

4. We now add a 2nd transform driver control, tip, that sits at the position of point_2 and drives the translation and rotation of point_2. Now when the root transform driver control is translated or rotated, point_2 no longer moves because it is constrained to the tip control:

   • Click beside the setups multiparm to add a new set of parameters for the tip control.

   • In the Settings tab, turn on use_t, use_r, and use_s.

   • In the Driven tab, set driventransforms to point_2.

   • In the Control tab, set driver to tip and driverguide to point_2.

   • Turn on makecontrol, promotet, and promoter.

   • Configure the control shape in the Shape tab.

5. When a transform driver control sits at a different position from the joint it is driving, the transform driver acts like a parent constraint - when the transform driver is rotated, the driven TransformObject and all its children rotate about the transform driver.