Gamasutra - Three-Axis Animation

This post will be on the notes I took on an article from Gamasutra on Three Axis Animation written by Jean-Michel Ringuet.

So, animating within 3D is pretty close to reproducing a realistic motion, 3D itself implies a world that obeys the same laws and physics as our - a world that is truly believable.

Gravity is the key here, it's the force that affects any movement within any universe to make it believable, the creation of a force is the basis for a motion in a 3D Space. With this mind, characters beed ti have a force that counterbalances the effects of gravity everytime you want to move it.

The example from the article:
If you have a standing character going from point A to B - there's two ways to solve the problem:
1. You can select the mesh of the character, or the center of gravity, and move it from A to B. The outcome is that you've created an artificial force that allows you to move the body
2. You can create motions, or forces, that will move the center of gravity from A to B. This is done by replicating the way a body moves in the real world.

Solution One: you are creating the illusion of movement.
Solution Two: illustrates a true comprehension and reproduction of the physical laws to create a movement.

Understanding how gravity is sued to creating movement is the first rule of the three-axis animation.

Every move starts out of balance and then by the end of the movement it's regained balance before falling down. The center of gravity is usually the first bone (or the root joint) of any character skeleton. The body is in balance when you can trace a vertical line from the pit of the neck to the ankle of the supporting foot. If the line isn't perfectly aligned then the body is not in balance.

This image helps emphasize the point of the paragraph above

Every movement makes a rotation of several rigid bones around articulations. on the other hand, in game animation's - there is NO flexibility at all in the skeleton. The muscles are built over the skeleton, their function is to create the motion of the rigid parts, muscle also creates force.

In the human walk cycle (the example used in the article):
- The first movement is the rotation of the right leg around the hipbone - lifting the right foot in front of the body.
- Trying to do this with your thigh muscles will result in your right foot sliding across the floor.
While there is nothing wrong this but sliding the foot requires more effort - you'll also be out of balance. Shifting your hipbone lifts your right foot up.

Tilting the hipbone has two affects:
1. It makes your right leg higher than the left - this allows rotation forward without your right foot sliding across the floor.
2. It makes the center of gravity to your left leg.
This then produces a different in-balance between the upper and lower parts of the body.

In this instance you'd have one part of your lower body higher than the other - the upper body has to compensate for that. This is the reason for why we tilt our shoulders in the opposite direction of the hips. We even tilt our head slightly to stay level with the ground.

Even though this may look simple in a 3D program - int he sense you'd just rotate one object around each pivot point, it actually requires rotations on many other parts of the skeleton. Understanding this, you'll start to understand the principle of three-axis animation: EVERY PART OF THE BODY HAS TO MOVE IN THE THREE DIMENSIONS TO CREATE A REALISTIC MOVEMENT.

This pretty much sums up the key points I took away from this article, thought it was really informative and when you look back at the example with the human walk cycle it really does get you thinking about it all and how it all makes sense after a while. I look forward to putting these notes into my own animations soon.