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Using Linked X-forms in Skeletal Animations

Before we link up the mesh to the skeleton we have to create some dummy objects to link to each bone. I've found that trying to link a mesh to bones that have had their pivots moved tends to screw up my linked x-forms, so as a solution I create a dummy object for each bone, name it after the bone I link it to, and link my verts to the dummies instead. Also using dummies allows you to do neet stuff like scale transforms to get those bulging biceps or expanding/contracting thorax effect (for models that like to breathe) without screwing with your skeleton. Try not to make the dummies too big - they really only need to be big enough to see. Position the dummy so that its center corresponds roughly with the center of the bone it will be linked to (not the bone's pivot). Once you have a dummy linked and named after each bone you can link the mesh.

To begin you must have an Editable mesh or at least apply an Edit Mesh modifier so that it is the last modifier in the stack. Starting at the feet we go into vertex edit mode and select all the verts surrounding the left foot bone - basically whatever verts that define the foot. With the foot verts selected you then apply a Linked X-form modifier, click the Pick Control Object button then open the Object Selection List from the top toolbar, select the left foot dummy and click the Pick button at bottom. Your foot verts should now be linked to the left foot dummy, which is in turn linked to your left foot bone. If you do a test rotation on the bone you should see the meshes' foot move accordingly. This is where you determine if you've linked too many verts or not enough to the bone, and if any of them need to be adjusted. If this is the case you don't need to delete the xform from the mesh stack, just go back to the edit mesh modifier (in the stack) where the verts were selected and make whatever modifications you need. You can move them around, add or remove some from the selection - whatever, as long as you have the ones you want linked selected when you go back to the top of the stack. You can try your test rotations on the bone again to see the effects of your vert adjustments if you made any.

When you are satisfied with the results, apply an edit mesh modifier again and repeat the procedure for the right foot (Linked X-forms must always be preceded by an Edit Mesh modifier). It is always best to work with bone pairs when doing linked xforms because any modifications you made with the first xform will be fresh in your mind for the second. Going fishing thru the stack after you've done 23 linked xforms and edit mesh modifiers can be a major ass pain if you've forgotten something, so try to resolve your xform issues in pairs and be done with it.

When you finish with one bone pair move up the heirarchy and repeat the Edit Mesh/Linked X-form procedure for the next bone pair or single bone in the case of the spine and pelvis, always testing as you go. When you are finished with the vert links you should run your skeleton through a thorough series of tests before animating. Check the mesh from different perspectives and pose it as much and as varied as possible. The more care you take in testing it the less hassle you have to deal with later on.

One more trick you can do with dummies (if you have the patience for LX-forms) is create a few extra to add at all your joint locations on the skeleton, and link a few joint verts to them. This helps distribute the vertex load between joining bones and allows for finer manipulation of verts at the joints. I've found that without the extra joint dummies you can get really gross distortion of verts at the joints (especially the shoulders). Note that adding joint dummies requires you to break some links by relinking children as children of the joint and then linking the joint to a parent. This should be done before the mesh is linked to the skeleton. Example: The forearm would be relinked to the new elbow joint and the elbow joint would then be linked to the arm. All you do is select and link to the new parent, since a child can only have one immediate parent bone, the old parent will be forgotten, regardless of any previous biological or emotional relationship. You also shouldn't have to worry about setting IK rotational limits to the joint dummies because you will really only be adjusting them minutely using FK rotations.

The trick with Linked X-forms is to visualize your verts and their relationship to the bones they will be linked to before you link them. Try to picture the effect that a bone will have on its surrounding verts as you move it.

Check it out!