How to Make Game Animation More Realistic

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What’s wrong with game animation: the center of mass problem

In most Hollywood action movies and game animation we see unnatural moves. These may be long jumps, powerful kicks that send humans to space, jumping off an explosion and so on. We don’t know what exactly is wrong, but we know it’s fake. And in old movies with Jackie Chan every move said moves look very natural and we actually believe in them. But what’s the difference between them?

The answer is simple: ropes. To make a character fly the cascadeurs use ropes. And to make a CGI character fly they use animation software. Ok, but why do flying CGI cars or helicopters look so natural and people don’t? Because while animating people or throwing them with ropes they do not pay respect for such basic physical constant as a mass.

Our brain always sees and keeps in mind how real people move under the force of gravity. On some deep level of our mind we know how a man must look when he jumps forward, even if it’s a 1 mile leap jump. And if our representation of such action doesn’t match the jump shown in a movie we consider it fake.

Video games have exactly the same problem: they do not use gravity force to animate the characters. As a result, they can animate wrongly even such a simple thing as walking. In this article we will tell you how to add a mass to animation and make it more natural in the eyes of the players.

Why game animations are physically incorrect

Center of mass is a virtual point of every physical body where the masses are balanced. For example, if you take a cube, locate it’s center of mass and place a needle directly under it, the cube will balance on the needle. There are some YouTube channels who balance things like motorbikes, laptops and rocks by discovering their center of mass.

Our brain may not know about it, but it is so used to seeing real objects with their center of mass balanced that it will notice every object whose behavior does not match real world physics. So what can we do about it? Add a center of mass to our animations.

First of all, the center of mass applies to humans and other living creatures. Our center of mass is located near the belly button. This point isn’t static: its location can be changed by redistributing the mass balance. If the person will move his leg forward, his mass balance will change and the center of mass will go forward too.

To save the balance the person would have to lean backward or to stretch his arm backwards. But they don’t do it in video games. Look at Kitana crouch kicking — in the real world she would fall because her body isn’t balanced.

So if you are doing animation by hand, you need to check the climax point of the animation to see if the person can maintain balance or not. If not — change his pose until it can.

Using inertia to make game animation look believable

The center of mass is the heaviest part of our body. And the weight means inertia — the amount of power you need to apply to make an object move. The inertia works in both ways: to start a movement and to stop it. So as the center of mass is the heaviest point, its movement must be the slowest and smoothest of all other points of a body.

In game animation it works this way: locate the center of mass and track it’s movement trajectory. Change the animation in such a way that this trajectory will be the shortest and smoothest of all body point trajectory.

Second part of inertia is ballistics. Ballistics is a science about calculating the trajectory of thrown objects. It’s simple: the trajectory will be parabolic for any symmetrical object with real weight.

If your character is jumping forward, his center of mass will move in parabolic trajectory. Of course, some games allow you to control a character in mid-air, but now we are talking about animation.

And the third part of inertia is that the object’s movement is born from the center of mass movement and not otherwise. So to make a character jump forward you need to show that its center of mass is moving first: it must lean forward before the jump. That’s all.

Kinetic energy transition and inertia

Every object has two kinds of energy: potential and kinetic. Potential energy is its mass and kinetic is mass multiplied by speed squared. We don’t need this formula to use a kinetic energy in game animation, but let it be here.

A kinetic energy or an impulse looks like a movement in one direction. To change the direction you need to apply a second impulse to the center of mass. To make the object move in the opposite way it has to lower its current impulse to zero and only after to apply a new impulse. In other words, to transfer its kinetic energy into potential and then transfer it to kinetic.

In animation it would look like this: the beginning of an animation is slower than its main part. It is so because of the natural transition energy from potential to kinetic.

We can use it to make the moves look more powerful. For example, if the character is swinging a giant sword, it must transfer the kinetic energy of his body to the sword. It looks like this:

  • first the character moves his center of mass to create an additional impulse;
  • then he moves his hands to transfer the impulse to the sword;
  • in the last frames of animation he stops his body from moving so the sword will have all the kinetic energy left and will move faster.

How to use it in games: you need to show energy transition while portraying a process of changing movement’s direction. The character, his fist or sword must stop completely and only after starting moving in the opposite direction.

How to improve game animation without headache

  1. Use the rotoscopy. There is no better way to make game animation look realistic other than copy it from real life.
  2. Buy a wooden doll for an artist. It has a metal pole and a stand to maintain balance. You need to take a pole from the stand, glue a spring to a stand vertically and then insert the pole in it. When the doll’s center of mass will be under the spring it will stand still. And when the center will be dislocated, the doll will lean in that direction. By doing this you can understand how it works, what moves causes balance loss and how to balance it with counter moves.
  3. Find a center of mass and try to make it’s trajectory as smooth as possible. Arms and legs can be swinging like airfans, but the center of mass movement must be very smooth.

If it seems to complex, contact us. We will help you to make realistic animations for whatever you need.

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