Raycasting - Unity Official Tutorials

Raycasting is the process of shooting

an invisible ray from a point, in a

specified direction to detect whether any

colliders lay in the path of the ray.

One such example of this would be

shooting a gun. In this instance our

character wants to shoot the evil box that

betrayed him and killed his father.

The syntax of the raycast function looks like this.

It can be confusing at first

but once you understand what each part does

it makes much more sense.

Firstly, the origin of the ray is a

point in world space.

So in this instance we'd choose a point in

front of the barrel of the gun, stored

as a Vector3, an X, Y and Z position.

However, because our world coordinates

direction won't be facing in the direction

we're shooting we will need a second Vector3

to store our direction in.

These two Vector3 variables make up

our ray. But we can also substitute

in a Ray variable, as this data type

can store two Vector3's.

Our code would then look like this.

The next argument in the function is a

RaycastHit variable that stores

information on the colliders hit.

So that it can be queried in code as to which

objects are intersected by the ray.

Finally there are two optional arguments,

Distance, which defines the length

of the ray, if omitted the ray will default

to an infinite length.

And Layer Mask. This is the number

of a particular layer in Unity's layer system

on which you can place objects if you

wish to make the ray ignore them.

Let's look at another practical example of

using raycasting.

In this example we have a parachute crate

that opens a parachute when it's

nearing the floor.

The crate is made up of two parts,

the chute and the crate itself.

The chute has two animations

one to open the chute

and another to close it.

In this example we need to cast a ray

downwards in order to see how far the crate is

from the floor, and we check for the

floor by looking for the environment collider.

Our collider for the environment is tagged

with the word environment.

And in our script we are looking for that tag.

The RayCast function gets placed inside

an IF statement so that if it returns true,

meaning if it intersects with anything,

then the comments within the IF statement

will be carried out and the RayCastHit

variable can be queried as to what has been hit.

So within an IF statement we've written

Physics.Raycast, we have a landingRay variable

that's storing the position of the box

and a downward direction. We're using

the shortcut Vector3.down,

and we're using this as the ray to cast.

Our RaycastHit variable - 'hit' -

is storing anything that gets hit by the

ray as it is cast downwards,

and the distance, or 'length' or the ray

is defined by our 'deployment height' variable.

If the ray intersects with a collider

then we call the deploy parachute function.

This function then simply sets our Boolean

'deployed' flag to true so that this cannot repeat.

And then we set the drag of the rigid body

to the variable 'parachuteEffectiveness'.

So we slow down the crate as if it's being

held up by the parachute.

We also play the animation

on the parachute object,

which is a game object that we'll assign

to the public variable.

We then have a separate OnCollisionEnter function

which simply plays the closing animation.

So we know that as soon as it hits the ground

or another object the parachute can close.

So here we've set the length of the ray to 4

by setting 4 as our deployment height

And we're setting the drag of the rigidbody to 8

by setting the parachute effectiveness to 8.

And we've simply dragged our parachute

chute object on to the parachute variable.

Because this is the object that has an animation

component in order to playback

it's opening and closing animations.

So let's see that play one more time.

It's also worth keeping in mind

that although you cannot see

raycasts drawn in the scene view

or in the game. You can also use the

Debug.DrawRay function

in order to preview where a ray would be going.

By adding Debug.DrawRay

we're drawing a visual ray from

the position of the box in the direction

of Vector3.down, multiplied by

the deployment height - the length of our existing ray.

And by doing this we've matched the actual

ray that we're casting in the IF statement below.

So when we play this back you can see that

Unity demonstrates the ray

by showing us the drawn ray in the scene view.