Giving a Model a Skeleton
A 3D model is a frozen statue. So how does it walk, wave, and dance? It needs bones.
A 3D model is a frozen statue. So how does it walk, wave, and dance? It needs bones.
Here is a 3D character. It looks ready to move, but it is only a shell of triangles: a mesh, like skin with nothing underneath. Press the button and try to make it wave.
A mesh is just a list of points in space. There is no elbow, no shoulder, nothing that knows how to bend. We have to build that in.
Rigging drops a set of bones inside the model, connected in a chain: spine, then shoulder, then elbow. Reveal the skeleton to see it. Notice the bones form a family tree.
Bones have parents. The shoulder is the elbow's parent. Move the shoulder and the elbow, forearm, and hand all follow, because they hang off it. This parent-child chain is the whole idea.
Each bone is bound to the skin around it. Rotate the shoulder and the whole arm swings. Rotate the elbow and only the forearm and hand bend. Try both.
Deciding how much each bone pulls on each piece of skin is called weighting. Good weights make an elbow crease naturally; bad weights make the skin tear or pinch. It is the trickiest part of rigging.
One set of bone angles is a pose. Line up a few poses and play them in order, and the character moves. Press play to run a wave built from just four poses.
Movie animators pose only the important frames, called keyframes, and the computer fills in the between-frames. A three-second action might have just five hand-made poses.
You learned how a lifeless mesh gets a skeleton, how each bone pulls the skin around it, and how a string of poses becomes animation. This is called rigging, and it is the step between a 3D model and a character that moves. Now try it on a real model.
A 3D model is a shell of triangles. It looks solid, but on its own it cannot move any more than a statue can.
Rigging adds bones connected in a chain: shoulder to elbow to wrist. Move a parent bone and every bone below it comes along.
Each bone is assigned the nearby part of the skin. When the bone rotates, that skin follows. This binding is called weighting.
One set of bone angles is a pose. Play a sequence of poses quickly and the character moves. That is how every animation is made.
Put your new knowledge into practice!