UE4 Career Pathway Movement Slides

How We Move

Movement in video games nearly always happens over time. When we want a player to walk forward, a unit to move to a target location, or a card to be played onto a board, we don't want them to reach their destination instantaneously.

Instead, for every frame we move the object by a small amount until it reaches it's destination. We can achieve this by updating the object's position value stored in it's transform using SetWorldLocation, SetRelativeLocation, AddWorldOffset or AddRelativeLocation.

//(Event Tick & Delta Time)

Lerp (Linear IntERPolation)

Sounds fancy and complicated, but it's really simple.

Every Lerp has 3 values: Origin (A), Destination (B), and Alpha
- The first two are simple enough, where the object comes from and where it stops at.
- The second one is the objects progress, a value from 0 to 1 to tell us how close we are to the destination
  - A value of 0 means we are still at the start position,
  - A value of 1 means we have reached the destination,
  - A value of 0.5 means we are halfway there,
  - .75 is 3/4ths the way to the destination, and so on.

Lerp: How

All three values of the lerp are often stored as private variables in the blueprint/class that is being moved.

Every frame we can increase the alpha value so it will be closer to 1.
- If we want to have the object take X amount of seconds, we can divide the current amount of time by the total time it should take.
  - For instance, if we want the object to reach the destination in 5 seconds and 2 seconds have already passed since the object started moving, the alpha value would be 2/5 or 0.4.

Lerp: Outside of Movement

Lerp can also be used outside of movement. Color, rotation, and scale can also utilize the lerp function.

Lerp can also smooth a change in direction, or act as friction.

Instead of using time for our alpha value, we can set alpha to a constant smoothness value.
- Our Origin (A) would be our previous value, and our Destination (B) would be the value we want to move smoothly transition to.
- Good values for smoothness are somewhere between .0625 and .25. Anything below will be a really slow transition, and above .25 will be really fast.

Lerp: When to Use

Besides transitions, there are plenty of places where a lerp is much more efficient and looks great in comparison to physics based movement.

Lerp works really well on UI elements and animations. If something takes a certain amount of time no matter how far from the destination you are, you'll want to use a lerp.

Motion Equations

Movement can also be Physics based, utilizing the Position, Velocity, and Acceleration model. This is often referred to as the Kinematic or Motion Equations.

By default, all Actors have a physics actor component attached. If you are using these physics calls make sure it is enabled.

We can modify these using AddLinearVelocity, SetLinearVelocity, AddImpulse, and AddForce.

We can modify location with the same functions mentioned previously.

Motion Model: How it Works

The physics engine automatically calculates the following equations before every frame:

acceleration = sumOfForces / massOfActor + gravityConstant;
location += velocity * deltaTime + 1/2 * accel * deltaTime^2;
velocity += acceleration * deltaTime;

Motion Model: Ways to Use

Projectiles: Bullets, Arrows, Laser Beams

There are three values you will want to set, and then never touch the projectile after that:
- Initial Position, Affected by Gravity (bool), and initial Speed.

Unpushable Objects

If you have an object that should not move unless the player gives input, or you say so, set the "isKinematic" value to true.

This will still allow you to move the object by using acceleration and velocity, and prevent the object from being pushed.
- A pong paddle is an example of a Kinematic object.

Actors in Unreal

Transform

Location

Location

Rotation

Rotation

Scale

Movement Types

How We Move

Lerp (Linear IntERPolation)

Lerp: How

Lerp: Outside of Movement

Lerp: When to Use

Motion Equations

Motion Model: How it Works

Motion Model: Ways to Use

Programs

Cyber Security Committee

Algorithm Practices

Mock Interviews