动作惯性跟随 & 动作重叠（Follow Through & Overlapping Action）
渐进 & 渐出（Slow In, Slow Out）
Adding Weight to Your Game Design
Follow Through & Overlapping Action
Applied to Animation
Whenever you have an action, it must always carry through to the next, and different parts of a body or performance move and stop at different times. How and when they stop shows their weight in direct relation to one another. Often times these two terms are used interchangeably but there is a subtle difference between them. Follow through means that separate parts of an object will continue moving after it has stopped. Overlapping action is the tendency for parts of the body to move at different rates and how that can be used to fluidly lead from one action to the next.
Let’s start with Follow Through. Think of energy. It can’t just stop. It has to transfer through, and past its destination. This follow through is what gives a sense of weight and connectivity through the body and performance as well as showing the player where the action originated from. In animation, lets again refer back to the jump. When you land, your body doesn’t just stop, even if you appear to. Even as your hips land first then rise back up, you compress your spine and your head begins to arch down. Your arms also drag behind, continuing the stretch into the squash. Those movements are the natural follow through of each body part. Now imagine as the character is landing, he goes into an uppercut. As his arms are falling, dragging behind and up above the rest of the body with the fingers open, they arc down, ball into a fist and then slam into the action of the uppercut. They don’t actually stop at any point in the action, but flow seamlessly from one action into the next, from trailing the body towards helping propel it into the punch. And that linking motion is the overlapping action.
Overlap of movement and performance is what brings a character to life and makes them look and feel alive. Without this, they are just a machine, going from one task to the next, losing all sense of emotional weight or soul.
Applied to Game Design
In game design, this means whatever the player does, or whatever happens in the world, it must have repercussions. It must go beyond just what was completed and towards what is going to happen next. Actions should link up, and what you just did affects what you are about to do. It doesn’t always have to be in the players face, but it must be felt, if you want the completed action to have any weight. And it is the repercussions of those players actions that is follow through. You shoot and your actions follow through into the world through either bullet holes, injuring an enemy, or blowing up a propane tank. In fact, this is the ultimate key to immersion. And while crafting a world with player freedom in which every action and decision has the same follow through as physic objects is a Herculean task, like every principle, the key is to feel it, not just see it. It can be in a simple audio cue. It can be in a slight head nod. Because like other principles, the follow through must match weight of the action. Heavier parts lag further and stop slower that something that is light. This is what defines weight and truth in actions.
Follow through is how everything reacts to what just happened, but it doesn’t always have to overlap into something else. In fact if everything is overlapping it becomes chaos. The overlap is reserved for what will be driving the next mission or action, to help the player feel what is essential to the experience. Without overlap, actions are hollow. Overlapping the outcome of one mission and how it leads into the next can make something as silly as going from an amusement park to the moon feel legit. It is especially important with NPC AI if you want to create a living, breathing world. It is the transitions, turns and look at commands that give the appearance of a thought process in a character. Unfortunately too often those are the first parts to be scraped or rushed when working on a character because they are boring to animate and are treated merely as a service to the progammers. But without the overlap of those transitions, NPC’s really become nothing more than pathing AI bots, which are hard to believe as actually moving around the world with any purpose. When designing an area, be aware of what your NPC characters could be doing there. When requesting a change in attack state, think about WHY they would do such a thing. This starts with anticipation, but without having that follow through, the anticipation will fall flat. Follow through is the squash to anticipation’s stretch. And if there is ever a time you can’t anticipate something, follow through is your golden parachute. If you want to move something very big very fast, you can cheat the sensation of weight by skipping the anticipation but making sure there is a lot of follow through to accommodate moving something of such a large mass so quickly. So even if it takes off like a bullet, give it the follow through of a train to maintain that sense of weight with all its other actions.
Overlap and follow through are what transform player interactions from being a mere skinner box into a deeply rewarding experience. If the use of achievements, trophies or badges are the only form of follow through we give out as developers, then we are not holding up our end of the conversation with the player. Follow through and overlap is how we answer a player’s question of with a sense of purpose and weight.（source:gamasutra）
Slow In, Slow Out
Applied to Animation
There is nothing worse than a jarring stop, or sudden change in direction to quickly take you out of a performance or action. Nothing ever truly comes to a complete rest, (unless it is dead) it is just moving at different speeds between one action and another. This principle also shows how heavy something is by how fast it starts or stops. In every action, there is some settle after something happens, or before it is about to happen. The first exercise every animator learns to illustrate this point is a pendulum. Throughout the middle of its trajectory, it moves very rapidly. But as it nears the apex of its arc, it slows down a bit. There is some friction there as gravity begins to pull it back down. And both before and after the apex, it loses some momentum. Until again, it begins to fall, at which point it picks back up. And while the word slow is in the name, it also defines how quickly an object moves to and from a state of rest.
This principle again builds upon squash and stretch, but beyond that it is what allows the player some time to feel and see the pose without it becoming static. It gives the animator time to transition from one pose to another and makes sure that the important poses are seen without them coming to a complete stop. This allows the action to read clearly and still feel alive. Depending on the action, animators can either ease in or cushion in. Ease in is just slowing into the pose like the pendulum shown above. Cushion in slows in, but then overshoots a bit before it settles back into the pose, like a car coming to a stop. Depending on the weight of the object depends on which is used, and the difference of both can be felt.
Applied to Game Design
In game design, it is easy to see the translation. With goals, the player should be gradually eased in and out of each task they are asked to complete. The complexity of each puzzle should be eased into. But a new gameplay mechanic can be a great way to cushion in. Give the player a new enemy to fight, by building up and slowing into that first encounter, then slightly stretching the next encounter to up the challenge, and then settle back so that they can feel a sense of mastery. The same can be done with a new power, as a way to let the player feel like they are exploring it a fair amount on initial discovery without overloading them with too much information. Just remember, weight matters. When you slow in and out a great deal, the player will assume that it is something of importance, because you are keeping their focus on it. If you give it only a little ease in and out the player won’t have enough time to truly become attached.
The level to which you slow in and out is the hard part to master, and that is what play testing is all about. Is this action too sudden and confusing? Then you need to slow out of the last action. Is the player lost because we didn’t give them enough time to digest what is happening at this moment? Then they need to be slowed into it so they can take it all in. Is this part not explosive enough because it is too slow and taking too long to get to the action? Slowing in and out is what gives each action weight, and what dictates their importance. If either are off, then the weight and truth of the game will be lost.
And when the slowing in and out becomes too obvious or slows down the overall gameplay, use some overlap, because remember, everything is connected. Slowing in and out allows you the time build in the overlap without everything becoming too hectic and disconnected.
Slowing in and out is the moment when the character is devising a plan. It hasn’t entirely anticipated the next action yet because it hasn’t decided what that next action is. It is what is going on as the overlap and follow through are taking place. And that is an important moment. That is the moment when things begin to stew. That is the moment when the pieces are being put together. That is the moment and sensation we are developing for the player with almost everything we do. We want them to think about what they are doing, what they are going to do, what they want to do because that is when they are fully invested and part of the game. And when they ultimately respond to what the game has asked of them, they will have had time to truly feel like they made a decision, and not just an action. That is the moment when both the game and player are occupying the same space and sharing each others weight. (Source: Gamasutra)