Joints and bones

From TOI-Pedia
It is very important to first make a plan of the movements of your character before you start creating it. If you know what movements your creature is supposed to be able to do you can create the skeleton according to this and you will not have to go through the trouble of adjusting the skeleton after it has it's control curves and/or binding to the skin. You will also not have to deal with the inconvenience of having joints that you don't really need. So first make a list of the movements your character will make and sketch on a picture of your character where the geometry needs to bend, because that's where your joints will need to be.

Creating a skeleton

To create a set of joints and bones the joint tool is used:


Now you can click the joints of your skeleton in your viewport. The joints clicked are automatically placed in a hierarchy, where the first joint you click will be the highest in this hierarchy, end the chain of joints with enter. Give the joints logical names:


Editing a skeleton

Moving and rotating joints and bones

If you have created the skeleton and you want to move a joint afterwards you can do this by selecting the joint and using your move tool. This way of moving your joint will cause the joints underneath it in the hierarchy to move along. If you don't want this to happen and you only want the selected joint to move, you have to go into pivot mode by pressing insert on your keyboard before moving the joint. Press insert again to exit the pivot mode. If you want to rotate the joint you can use your rotate tool and every joint underneath it in the hierarchy will rotate along:


Orienting your skeleton

If you have adjusted your skeleton in the pivot mode your joint probably won't be aligned anymore with the bone belonging to it (the red axis in the joint has a different angle than the bone). Later on this can cause problems, so make sure the bones are aligned correctly by selecting the entire hierarchy and going to skeleton > orient joint > optionbox. Make sure that in the optionbox at the hierarchy entry 'orient child joints' is turned on. Then press orient:


It is also convenient to make sure that the z-axis's of all your joints point in the same direction. If you select the entire hierarchy you can see in all your joints a little coordinate system to show the orientation of the joint. If one of the blue axis's is directed in another direction than the others, select the joint, and type xform -ra 0 180 180;:


Labeling your joints

Labeling your joints can help to make your scene clearer. To attach a label to your geometry select the joint and open the attribute editor (ctrl+A) and look up the joint labeling section. Choose the right side, the type of joint (if the right type is not in the list, select other and type the joint label) and check the draw label box:


Parenting and hypergraph

As you can see you can create a singular hierarchy of joints in the same direction by just using your joint tool, but if you want to create a joint that has two series of joints connected to it (you need to connect both legs to the pelvis for instance) you have to do it differently. An easy way to do this is parenting it. The hypergraph is a convenient window to use when parenting, you can find the hypergraph under window > hypergraph:hierarchy:


If you don't see all your objects in the hypergraph press A on your keyboard to show all.

First duplicate and name the leg to create the right leg and create a single joint (going nowhere) in the middle of these (for instance by using the gridsnap options):


One way of getting these bones attached to the pelvis is parenting them through the menu: select one of the hip joints and then the pelvis joint and go to edit > parent (shortcut: select them and press p on your keyboard):


You can see that a bone is automatically created between the pelvis and the hip.

You can also do this directly in the hypergraph. Select one of the hips in the hypergraph and drag it with your middle mouse button onto the Pelvis:


You can create and parent the rest of the skeleton in the same way. Mind that it's easiest to create the spine by beginning at the bottom and moving upwards, placing the joints at the right spot (you can pointsnap to joints, so to get the spine above the pelvis you can draw it in your sideview and pointsnap the spine in the x-direction to the pelvis), orienting them, naming them right and labeling them:


After that you can attach the spine to the pelvis by parenting it to the pelvis through the menu or by MMB dragging it in the hypergraph:


When you are drawing an arm, to be able to animate the motion of the forearm you need to create an extra joint in the middle of the forearm. When you have drawn one arm you can mirror it to create the other arm by selecting it and going to skeleton > mirror joint and choosing the option box, there you need to fill in in which axis you want to mirror it. In this case we need to mirror it in the YZ axis:


Place the new shoulder at the right spot and don't forget to rename and relabel it to the right side before parenting both shoulders to the collar joint:


Before you start creating the handles for moving your skeleton make sure that the skeleton 'fits' your character, it is quite difficult and a lot of work to adjust the angles and shape of your skeleton after you have created the handles.


There are now 2 ways of getting your skeleton to move: Rigging for Forward Kinematics and Rigging for Inverse Kinematics. You can use one of these methods or a combination of both to animate your character.

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