USING
THE SKIN MODIFIER
This
tutorial will show you how to skin a leg using the skin modifier. The same
process can be applied using a full body.
1.
Download
and open
the File Legbones01.max. This file
contains a simple mesh of a leg, and a very basic skeleton.
2.
Select the leg mesh
3.
Apply a skin modifier
4.
Click on “Add Bone” under Parameters
5.
Select Bone01, Bone02 and Bone 03 (we don’t need Bone04 as it is just
that little bone on the end which we use to set up the IK). Click Select.
6.
Click “Edit Envelopes”
7.
Choose Bone01 (just beneath Edit Envelopes button)
8.
Now we will adjust the size of the envelope for bone one:
9.
Make the Right Viewport bigger and change it to “smooth and
highlights”
10.
Zoom into Bone01
11. You
will see that there are two envelopes, a brown one and a red one. The red one is
the “absolute” influence of that bone, and the brown one specifies the
“falloff” distance. This concept is the same as using “hotspot” and
“falloff” when working with a spot-light.
12.
Re-size and move your envelopes so that all of the thigh area is within
the absolute envelope:
13.
Now do the same for the Shin bone (Bone02). You will notice that as you
increase the size of the envelopes, we start to get a gradient of colours
appearing around the knee as the two bones “fight” for control over the
verticies.
14.
Notice how I have re-positioned the envelopes as well as re-sizing them.
15.
Now
do the same for the foot. Make sure you check in more than one viewport or you
may miss some verticies.
16.
Now we have done our basic skinning, we need to check it. The best way is
to make a small piece of animation so that we can keep scrolling back and forth
to check.
17.
Turn on the animate button.
18.
Go to frame 30
19.
Select the dummy “foot-control” (you will need to turn of “edit
envelopes” first).
20.
Move it so as to bend the leg. The idea is to bend the leg as far as you
will need it to bend in your animation. There is no point spending hours
skinning a leg so that it can bend right back if that is never going to happen
in your animation. A simple walk cycle doesn’t require too much bending.
21.
Turn off the animate button and scrub the timeline to frame 0.
22.
Now we’ve created that keyframe, we can scrub through the leg bend
whilst in the skin modifier by scrubbing the timeline.
23.
You may have noticed that the area behind the knee doesn’t exactly look
pretty at the moment. This is where we use the “Angle Joint Deformer Gizmo”.
24.
Select your Leg Mesh
25.
Click “Edit Envelopes”
26.
Select Bone02 (shin bone).
27.
Make sure you are at frame 0. This is important, because we want to add
the deformation gizmo at a point at which the leg is ok.
28.
Now we need to select some verticies to add the gizmo to. By default, we
cannot select verticies, so go to “filters” and tick the checkbox “verticies”.
29.
Now select all the verticies around the knee joint by dragging a
selection marquee.
30. Now open the rollout “Gizmos”
and click “Add Gizmo”. “Angle joint deformer” is already selected by
default.
31. This creates an FFD box around
the joint. We can now alter the FFD Box with the leg bent at different angles,
and Max will create keys based on the angle of rotation. I.e. “when the leg is
bent this far, I want the FFD box to be this shape, when the leg is bent a bit
further, I want the FFD box to be this shape etc etc.
33.
Under
“Gizmo Parameters” click on “Edit Lattice”.
34. You can now select the control points of the lattice and move them to create keyframes at different angles of rotation. Scrub the timeline to alter the angle. NOTE: these keyframes we are creating are NOT based on time, but on ANGLE. We can delete the animation of the leg bending and it won’t affect the keyframes we have created for the joint angle deformer. Note that the control points turn red when you scrub past a frame/angle where you have already created keys. Try to only use a few different frames/angles to create keys as this keeps it simpler to manipulate. I know it sounds complicated, but it’s really not once you have a few goes. Honest.
35. TIP. Work in the Right viewport (or any orthographic view), and always use a selection marquee to select the control points, as you are actually selecting two points. (look at it in the perspective viewport and you’ll see what I mean).
36.
That’s really as much as I can show you in a written tutorial, the only
way you can figure out how to do good skinning is to practice it.
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