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  • 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.

Raycasting is the process of shooting

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Raycasting - Unity Official Tutorials

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    朱瑛 posted on 2014/05/02
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