NHR-5 – Fixing Bone Roll

Now that we have defined our new shape, it’s important to fix the bone rolls. Bone rolls values are extremely important to let the rig work correctly during animation, avoiding tedious and sometimes almost impossible fixes. These values will determine which is the natural bending direction of each single bone in this rig. This is the reason for that long explanation about joint orientations, bvh standard and the in depth discussion of how to setup bone roll: it is what we have to comply with now.

One major aim of this course is also to give you knowledge at hand that allows you to understand what Avastar does under the hood. Thus we are looking behind the curtain instead of just telling you about magic buttons and cook book solutions. So be prepared to get into some details.

The course is separated into 7 lessons. This is lesson 5 (updated for Avstar-1.2)

• The anterior Legs (front)
• X Mirror
• Anterior Legs chain
• Recalculate Bone Roll
• Quickfix for flipped X Axis
• Check the Deform Bones
• Adjust the Deform Bones
• More about Snap
• Check the Rest Pose
• Bone Display Style
• Snap Rig to Pose

Here is an example of the anterior leg not fixed yet (see image)

As you can see, the Y axis is pointing down along the leg, as it should. But the other axes point to the wrong directions:

• The X-Axis points forward
• The Z-Axis points sidewards

Now since what was an arm in the original Skeleton is now used as anterior leg for the horse, so also the bone rolls of the anterior legs should comply with that.

Note: The bone’s local Axes are displayed at the Bone Tails and not at the Bone Heads!

The X axis must point to the actual World’s +X (positive direction, where the manipulator handles in Global mode points at), while the Z axis is going to rotate along with it and point backwards in this case.

• Select a bone (in this case the front leg shin on our horse) and open the View Properties panel (N on the keyboard). In the Transform Panel you find a slider labeled “Roll”, which is currently set to ~90°.
• Lets modify that value such that the x axis now points sidewards (actually you will see the value is 0°) and see what happens..
  

Now the bone roll is fine: The X axis is pointing where it’s supposed to. And the Z axis is rotated accordingly. We should also notice that this change was propagated to the other side too, so we’re cool about it as we only need to do half of the work, and Blender will handle the rest.

Now proceed and do what you have done for the front leg shin with every single bone we have in the front leg, paying attention to where the X axis is pointing.Then proceed with the anterior legs (on the backside) in the same way.

Finally take care of the spine and head of your horse, always take care to let the local X-axis point towards the characters left side (as seen from first person perspective).

When we’re done, the anterior leg should look like in the image. This chain now complies with BVH standard as leg. And all other bones of the horse should also point in the same direction (towards left side).

 

In order to see what happens, please make the Base Skeleton visible (Tool Shelf, Show bones panel). Now you can see, that apparently the Base Skeleton has not been modified at all during our editing session. So we have to fix this next. But before we do this, lets take another look into the Armature in Pose mode.

However Avastar has a feature for this: Snap Base to Rig. This function is located in the Tool Shelf. It is only available for Armatures in Edit mode. As soon as you click on this button, the entire Base Skeleton will be recalculated and automatically snapped to the corresponding control bones of the Control Rig.

… Right after the Snap Base to Rig tool was called as described above, you will find the tool’s Operator Panel in the lower left corner of the Tool Shelf. There you find 2 snapping options: for the SL Base and for IK Bones

We need to ensure our rest pose is clean. This is necessary in order to have Blender export a correct Collada file with the new bones shape. We can check that out ourselves. Right now, the rest pose has not been applied yet.

Go to Object Data panel in the Properties window. There you find two buttons labelled Pose Position and Rest Position (see image)

Clicking on the buttons labeled Pose Position and Rest Position might show slightly different poses. We will fix this in the last step of this lesson where we ensure to snap to the correct Rest Pose.

If you see no differences when you toggle between the Rest position and the Pose Position, then all is well already, so don’t worry. In any case you should see something like in the next image.