Raycasts in Unity, made easy

The Raycast function is extremely useful for creating connections between objects in Unity.

For example, if you want to select an object just by looking at it or clicking on it.

Or if you want to shoot an object with a weapon or obstruct a line of sight.

Or perhaps if you need to check how high the player is from the ground, or what it is they’re standing on.

That’s where Raycasts can help.

So… what is the Raycast function and how does it work?

Raycast in Unity is a Physics function that projects a Ray into the scene, returning a boolean value if a target was successfully hit. When this happens, information about the hit, such as the distance, position or a reference to the object’s Transform, can be stored in a Raycast Hit variable for further use.

This makes Raycast extremely useful for getting information about other objects, performing ground checks or, generally, doing anything that involves a line of sight connection between two objects.

However…

While Raycast can be very straightforward to use, it can be a little unintuitive at first.

And if you’re new to Unity, the large number of features available, not to mention the many different versions of Raycast, each with their own quirks, can make it daunting to use at first.

But don’t worry, because, in this article, I’ll show you everything you need to know about using Raycast in Unity, step by step,

Let’s get started…

Here’s what you’ll find on this page:

• How to use Raycast in Unity
  • How to create a Ray
  • How to use the Raycast Hit variable
  • How to use the Raycast function
  • The different features of the Raycast function
  • What’s an Overload Method in Unity?
  • Limit the Raycast Range by entering a Max Distance
  • How to use Layer Masks with Raycasts
  • How to ignore trigger colliders when using Raycast
• How to hit multiple objects using Raycast
  • How to use Raycast All
  • Raycast All vs Raycast Non-Alloc
• Other types of Raycast
• Should you use Raycast in Fixed Update or Update?
• How to use Raycast in Unity in 2D
  • Raycasts in 3D vs Raycasts in 2D

How to use Raycast in Unity

The basic version of Raycast is made up of three different parts:

• A Ray variable
• A Raycast Hit variable
• The Raycast function

Here’s how each of them work…

How to create a Ray

A Ray is simply a data struct in Unity that represents a point of origin and a direction for the Ray to travel.

In its most basic form a Ray is an origin and a direction.

The origin is the position in the world that the Ray will start from and takes a Vector 3 value.

While the direction property takes a trajectory in the form of a normalised Vector 3.

Normalising a vector limits its magnitude, which is the length of the Vector, to 1, which is useful for representing a consistent direction.

There are a few ways you can create a new Ray.

You can create a Ray manually,

Like this:

// Creates a Ray from this object, moving forward
Ray ray = new Ray(transform.position, transform.forward);

Or, alternatively, you can use one of the helper functions to create a Ray automatically, such as a Ray that starts at the center of the camera’s viewport,

Like this:

// Creates a Ray from the center of the viewport
Ray ray = Camera.main.ViewportPointToRay(new Vector3 (0.5f, 0.5f, 0));

In the above example, the 0.5f values represent the middle of the viewport in both dimensions.

Or from the Mouse Position on the screen,

Like this:

// Creates a Ray from the mouse position
Ray ray = Camera.main.ScreenPointToRay(Input.mousePosition);

• How to Convert the mouse position to world space in Unity

These helper functions make it easy to create a Ray from an existing point in the world.

However, while you can cache a reference to the Ray you create, you’ll still need to update it every time you use it.

So, for example, if your Ray’s origin and direction are going to be different every frame, you’ll need to update the Ray every frame too.

Like this:

Ray ray;

void Update()
{
    ray = transform.position, transform.forward;
}

 Otherwise, when you come to use the Ray, it won’t be in the right position.

How to visualise Raycast in the scene

Using Debug.DrawRay, you can check if your Rays are going where they’re meant to.

Did you know you can visualise Rays in the game world?

The Debug Class includes a function, Draw Ray, that allows you to render a Ray in the world.

Like this:

Debug.DrawRay(Vector3 origin, Vector3 direction);

This function can be useful for making sure your Ray is going where you want it to.

For example, I could define a Ray variable for use in Raycast functions.

Like this:

Ray ray = new Ray(transform.position, transform.forward);

And then, render a visible line using Draw Ray, passing in the same values as I used to create my Ray.

Like this:

Debug.DrawRay(ray.origin, ray.direction * 10);

Notice that I’ve multiplied the direction value by 10.

This is because the Vector 3 that’s used for direction in Ray variables is normalised (meaning that it will have a magnitude, the length, of 1).

Multiplying the direction value by the distance of the Ray, in this case by 10, means I can match the length of the Ray I actually use with the length of the drawn line.

Once you’ve decided where your Ray will start from and which direction it’ll go in, you’ll need a place to store the data you get from it.

That can be done with a Raycast Hit variable.

How to use the Raycast Hit variable

The Raycast Hit variable is a data struct that stores information about Ray’s collision.

It records information like where the hit happened in the world, what object did the Ray collide with and how far away it was from the origin of the Ray.

To use it, all you need to do is declare it:

// Container for hit data

RaycastHit hitData;

Then, later, when you use Raycast to fire a Ray into the scene, you’ll have a place to store any information retrieved from the hit.

For example, you can get the position of the hit in the world using RaycastHit.point:

Vector3 hitPosition = hitData.point;

Or the distance from the Ray’s origin to the point of impact using RaycastHit.distance:

float hitDistance = hitData.distance;

You can also get information about the Collider that was hit, such as its Tag.

// Reads the Collider tag

string tag = hitData.collider.tag;

Or, you could even use Raycast Hit to get a reference to an object’s Transform:

// Gets a Game Object reference from its Transform

GameObject hitObject = hitData.transform.gameObject;

While the Ray and Raycast Hit variables define where a Ray will go and how information from hits will be stored, they don’t do anything on their own.

So, to actually fire Rays into the scene, and check if they hit anything, you’ll need to use the Raycast function.

Here’s how to do it.

How to use the Raycast function

The Raycast function in Unity allows you to check if a Ray collides with another object in the scene, saving the hit data to a Raycast Hit variable if it does.

There are several different versions of Raycast, each from different classes, that can be used in different ways, however, one of the most common ways to use Raycast is using the Physics Class, which returns a boolean true or false, depending on if the Ray hit anything.

Like this:

void FireRay()
{
    Ray ray = new Ray(transform.position, transform.forward);
    RaycastHit hitData;

    Physics.Raycast(ray, out hitData);
}

This will fire the ray that you’ve created into the scene and save information about anything that’s hit to the Raycast Hit variable you declared.

This works because of the Out Keyword in the function.

bool IsAboveTen(float num)
    { 
        if(num > 10)
        {
            return true;
        }
        else {
            return false;
        }
    }

void Start()
    {
        bool result = IsAboveTen(20);
        // result will be set to true;
    }

    public string numResult;

    private void Start()
    {
        bool result = IsAboveTen(20, out numResult);
        Debug.Log(numResult);
    }

    bool IsAboveTen(float num, out string result)
    {
        if (num > 10)
        {
            result = "The number was more than 10!";
            return true;
        }
        else
        {
            result = "The number was not more than 10!";
            return false;
        }
    }

Raycast takes an out Raycast Hit argument, meaning that a Raycast Hit variable will need to be specified when you call it.

Then when the function runs, Raycast Hit data will be stored in the variable you specified, allowing you to access it.

The out keyword allows you to save information in addition to the return type of Raycast.

So what is the return type?

Physics.Raycast has a bool return type, which returns true if the Ray hits a target.

This means that you can place the Raycast function in an if condition.

Like this: 

void Update()
    {
        Ray ray = new Ray(transform.position, transform.forward);
        RaycastHit hitData;

        if (Physics.Raycast(ray, out hitData))
        {
            // The Ray hit something!
        }
    }

Using Raycast in this way means that code inside the if condition will only run if the Ray actually hits something.

This is useful because it means that you can limit your code to only use Raycast Hit data when it actually exists.

Or to only perform an action if the Raycast was successful.

Whether a Raycast was successful or not typically depends on if it hit something, however, because of the additional features of the Raycast function it’s possible to limit what counts as a successful hit in other ways as well. 

Such as limiting the distance the Ray can travel, excluding certain layers or choosing if trigger colliders should be ignored.

Which of these settings are available to you depends on which overload method of the Raycast function you decide to use.

The different features of the Raycast function

There are many different versions of the standard Raycast function and each one offers slightly different functionality.

For example, some versions of Raycast only take a few parameters and perform a simple function in return, while others accept more complex sets of data and do more with it.

These different versions are Raycast’s overload methods.

What’s an overload method in Unity?

An overload method is simply an alternative version of a method that takes a different set of parameters and that may return a different type of value.

For example, the most basic version of Physics.Raycast takes only one parameter, a Ray:

if (Physics.Raycast(ray)) 
{ 
    // The Ray hit something
}

While using a different overload method allows you to specify a Ray, a Raycast Hit variable, a Max Distance, a Layer Mask (to include or exclude certain layers from being hit) and a Query Trigger Interaction setting, which determines if Trigger Colliders can be hit or not.

Like this:

public LayerMask layerMask;

    void Update()
    {
        Ray ray = new Ray(transform.position, transform.forward);
        RaycastHit hitData;
        if (Physics.Raycast(ray, out hitData, 10, layerMask, QueryTriggerInteraction.Ignore))
        {
            // The Ray hit something less than 10 Units away,
            // It was on the a certain Layer
            // But it wasn't a Trigger Collider
        }
    }

Overload methods allow you to pass different information into a function to achieve different results. 

How do you select an overload method in Unity?

A specific overload is defined by the parameters that are passed into it and their order.

So, to select a certain overload, simply pass in the set of parameters that match the overload you want to use.

How can you tell which parameters you need to enter?

Depending on your text editor, you may be able to preview what other functionality a method can support, as you’re writing it.

Like in Visual Studio, using the up and down arrow keys:

Each overload method is made unique by the parameters it accepts, and no two overloads can accept the same parameters in the same order.

Because of this, to use an overload method, you’ll need to enter the exact set of parameters it requires, in the right order.

Otherwise, it won’t work.

This can sometimes mean that, to use a specific overload, you may need to pass in parameters for functionality you don’t actually need.

But don’t worry…

Raycast supports a large number of overload methods (16 at the time of writing this) so chances are good that one of them will offer the functionality you want with minimal extra fuss.

So what can you do with different Raycast overload methods?

Limit the Raycast range by entering a max distance

Most of the overload methods available for Physics.Raycast also allow you to specify a max distance as a float value.

Like this:

Ray ray = new Ray(transform.position, transform.forward);

if (Physics.Raycast(ray, 10))
{ 
    // Hit Something closer than 10 units away
}

Setting a max distance can be useful for creating distance-limited functionality, such as weapons that can only shoot so far, or simply to avoid complications from Rays that extend infinitely across your scene. Not only is it useful, it’s also good for performance to limit the extent of a Ray, which is why it’s no surprise that many of Raycast’s overload methods (12 to be precise) accept a parameter for max distance.

While setting a distance can be useful for limiting the reach of a Ray, there will often be times when Raycasts intersect with many different types of collider.

How you distinguish between the different types of objects in your game is entirely up to you.

However, one option that works particularly well with Raycasts, is to use layers.

How to use Layer Masks with Raycasts

One of the most helpful features of the Raycast function is the ability to filter out colliders depending on their layer.

This allows you to completely ignore objects on layers that aren’t intended to collide with Raycasts.

As you can imagine, this can be extremely useful when you’re working with a large scene, with many different types of objects and colliders and you only want to check for collisions against some of them.

So how does it work?

For example, let’s say that all of the environment objects in my scene are on the same layer, the world layer, and that I only want to detect collisions on that layer.

All I need to do is declare a public Layer Mask variable…

Like this:

public LayerMask worldLayer;

Set it in the Inspector to match the world layer:

And then, in my script, pass the Layer Mask variable into the Raycast function.

Like this:

public class CameraRay : MonoBehaviour
{
    public LayerMask worldLayer;

    void FireLaser()
    {
   
        Ray ray = Camera.main.ViewportPointToRay(new Vector3(0.5f, 0.5f, 0));

        if (Physics.Raycast(ray, 10, worldLayer))
        {
            Debug.Log("You hit a wall, good job!");
        }
    }
}

In this case, I’m using an overload method that accepts a Ray, a Max Distance and a Layer Mask variable.

In order to use this version of Raycast I have to add all of those parameters in the correct order.

Otherwise, it won’t work correctly.

How to enter the layer number directly when using Layer Masks with Raycasts in Unity

Using a public Layer Mask variable is the easiest way to use Layer Masks with Raycasts.

However, if you want to do it all in scripting, and pass in the value of the Layer Mask directly, here’s how to do it.

If you’re anything like me, and because the Layer Mask parameter takes an int value, you might assume that you can just enter the number of the layer, for example, layer 9, in the Raycast function and that will work.

It won’t.

This is because, while the Layer Mask value is an int, Unity uses the binary representation of the integer to decide which layers will be checked and which will not.

Let me explain…

Imagine all of Unity’s 32 possible Layers as a row of zeroes, starting with the first layer (layer 0) on the right.

Now, let’s say that I want to check Raycasts against one of those layers.

For example, layer 9.

Layer 9 is tenth in the list, so if I change the tenth zero from the right to a 1, like this:

Changing the tenth digit from the right to a 1 represents the 9th layer.

Unity now knows that I only want to check Raycasts against layer 9.

Except that this is still a binary value. It’s still not the integer number that the Raycast function requires.

So how do you convert it?

Binary numbers work by counting, from right to left, which multiples make up a number.

For example, the number 8, in binary, is 1000. Because it is made up, from right to left, of no ones, no twos, no fours and one eight:

Whereas Nine, would look like this:

The binary value I’m using, when converted to an integer, is 512.

The decimal value for the 9th layer is 512.

Which I can add directly to the Raycast function to indicate that I want to check collisions on layer 9.

Like this:

if (Physics.Raycast(ray, 10, 512))
    {
        // Layer 9 was hit!
    }

I could even use the binary value to indicate multiple layers.

For example, layer 9 and layer 4:

The decimal value for the 9th and 4th layers is 528.

Which works out to be 528.

if (Physics.Raycast(ray, 10, 528))
    {
        // Layer 9 or 4 was hit!
    }

How to convert an Int to a Layer Mask value

While converting a binary value to an integer works, it isn’t the most convenient method.

Especially if all you want to be able to do is enter the integer value of the layer you want.

Luckily there’s an easy way to directly add layer numbers in scripting.

The bitwise left shift operator.

The bitwise left shift operator (<<) moves the bits of a binary value to the left by a defined amount.

Why is this useful?

It allows you to quickly enter a Layer Mask value without having to check what it would be in binary first.

To use it, simply shift the bit values of the number 1 over by the number of the layer you want to use.

For example, to enter layer 9, I’d simply shift 1 by 9.

Like this:

if (Physics.Raycast(ray, 10, 1<<9))
    {
        // Layer 9 was hit!
    }

This works best when you want to identify a single layer to detect collisions on.

But what if you want to detect collisions on all of the layers in a game except one, how could you do that?

Detect Raycast on all layers except for one

Just like when using a Layer Mask to limit collisions to a certain layer, It’s possible to invert the Layer Mask value so that it detects collisions on every layer, except for one.

This can be done with the bitwise NOT operator.

The bitwise NOT operation use the tilde symbol (~) and will flip every bit in a value, essentially inverting it. 

For example, if I want to detect collisions on every layer, except for the world, I can simply invert the Layer Mask value.

Like this:

public LayerMask worldLayer;

void FireLaser()
{
    Ray ray = new Ray(transform.position, transform.forward);

    if (Physics.Raycast(ray, 10, ~worldLayer))
    {
        // Something other than the world was hit!
    }
}

If you’re adding the Layer Mask directly to code using the bitwise operator, you’ll want to place it in parentheses first, so that the bitwise operation is carried out before inverting the value.

Like this:

Ray ray = new Ray(transform.position, transform.forward);

        if (Physics.Raycast(ray, 10, ~(1<<9)))
        {
            Debug.Log("something else was hit");
        }

While layers can be incredibly useful for including or excluding entire categories of object, you may still find yourself needing to exclude specific colliders from being hit.

For example, you may not want Raycasts to hit trigger colliders in the world but it may be that placing them on a separate layer just isn’t an option.

Luckily, there’s an easy way to exclude or include trigger colliders from receiving Raycast hits.

How to ignore trigger colliders when using Raycast

By default, Raycast will hit triggers, meaning that if a Raycast impacts a trigger collider, it’ll behave in the same way as hitting any other collider.

It’s possible to change this behaviour, either globally via a project setting or on a per Raycast basis.

How to disable all Raycast Trigger collisions

The easiest way to disable all Raycast trigger collisions is to simply turn them off.

Open Project Settings, select the Physics menu (or Physics 2D menu if you’re working in 2D) and uncheck Queries Hit Triggers.

If you don’t want Raycasts to collide with any triggers, just turn them off!

Now, by default, Raycasts will ignore all trigger collisions.

Even with this setting turned off it’s still possible to override the behaviour of individual Raycasts using the Query Trigger Interaction parameter.

Like this:

void FireLaser()
    {
        Ray ray = Camera.main.ViewportPointToRay(new Vector3(0.5f, 0.5f, 0));
        if (Physics.Raycast(ray, 10, worldLayer, QueryTriggerInteraction.Ignore))
        {
            // Whatever you hit, it wasn't a trigger
        }
    }

In this overload method, I had to enter a Ray, max distance and Layer Mask in order to use the Query Trigger Interaction feature.

You might also have noticed that Query Trigger Interaction isn’t a true or false boolean value.

Instead, it’s an enum, which is essentially a set of named values, allowing you to choose one of 3 options:

Ignore – overrides the Raycast to ignore trigger collisions.

Collider – overrides the Raycast to accept trigger collisions.

Use Global – which defers to the default value set in the physics options.

Using the built-in functionality of Raycast’s overload methods is the easiest and the most appropriate way of filtering out objects that you don’t want Raycast to hit.

It allows you to completely ignore certain objects, or even entire layers of objects, that aren’t intended to be used with Rays.

Which is great for reducing the number of objects that could be hit.

But what if you want to hit more objects?

And what if you want to hit multiple objects all at once?

For example, if you want to create a weapon that can cut through multiple enemies or detect multiple objects using a single ray.

After all, the default Raycast function stops after hitting a target, so how can you fire a Ray that can pass through multiple objects?

Here’s how…

How to hit multiple objects using Raycast

While Raycast is useful for identifying or colliding with single objects, sometimes you might want to use Raycast to detect collisions against multiple objects using the same Ray.

For example, you might want to create a weapon that fires through multiple enemies.

Or you might want to be able to detect and count how many objects are within a certain range.

For that, you’ll need to use Raycast All.

How to use Raycast All

Raycast All works a lot like Raycast, except that instead of hitting and returning only one object it can return multiple objects, storing them in an array.

To use Raycast All, you’ll need to declare an array of Raycast Hit variables and assign them when you call the Raycast All function.

Like this:

public RaycastHit[] hits;

void Update()
{
    Ray ray = new Ray(transform.position, transform.forward);
    hits = Physics.RaycastAll(ray);
}

Raycast All is useful for getting information about multiple objects using a single Ray.

For example, you could count how many colliders were hit by a Ray.

Like this:

int numObjectsHit = hits.Length;

Or you could destroy all of the objects in a Ray’s path.

Like this:

public class CameraRay : MonoBehaviour
{
    public RaycastHit[] hits;

    void Update()
    {
       if(Input.GetMouseButtonDown(0))
        {
            FireLaser();
        }
    }

    void FireLaser()
    {
        Ray ray = new Ray(transform.position, transform.forward);
        hits = Physics.RaycastAll(ray);

        foreach(RaycastHit obj in hits)
        {
            Destroy(obj.transform.gameObject);
        }
    }
}

Raycast All works great for getting all of the objects that collide with a Ray.

There’s just one problem…

While Raycast All can detect multiple colliders, it retrieves them in an undefined order.

So, while it’s often helpful to think of Raycast All as a laser travelling through objects one by one, it doesn’t actually happen that way.

Instead, all of the objects that are intersected by the ray are detected at the same time, and the order in which they’re added to the array can’t be guaranteed.

This means that, for example, if you wanted to destroy multiple objects in a line by firing a ray through them, one by one, they won’t be destroyed in order along the Ray’s path.

Instead, it will more than likely happen randomly.

This isn’t necessarily a problem if you’re carrying out an action on all of the objects at the same time.

However, if you want to get the objects in order from the origin of the ray, you’re going to need to sort the results.

Here’s how to do that…

How to detect Multiple Raycast hits in order (by sorting the array)

There are a ton of different ways to sort array and list results in Unity.

However, in this example, I’m going to show you one of the simplest methods I’ve found to sort an array, without converting it to a list first.

For this to work, you’ll need to add the System Namespace to the top of your script:

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using System;

Then, once you’ve got the Raycast Hit results stored in an array, you can sort their order.

Like this:

void FireLaser()
{
    RaycastHit[] hits;
    Ray ray = new Ray(transform.position, transform.forward);
    hits = Physics.RaycastAll(ray);

    // Sorts the Raycast results by distance
    Array.Sort(hits, (RaycastHit x, RaycastHit y) => x.distance.CompareTo(y.distance));
}

This function basically determines how any two results (x and y) should be compared.

In this case, they’re being compared by their distance, which is a property of the Raycast Hit struct and is measured from the origin of the Ray to the point of impact with the collider.

Raycast All vs Raycast Non-Alloc

Raycast Non-Alloc is an alternative version of Raycast All that works in a similar way, except that it doesn’t generate any garbage.

This is because, while Raycast All returns a new Raycast Hit array each time it’s called, Raycast Non-Alloc stores its results in a fixed array, which limits the number of results it can return.

When you call it, the function returns an integer, equal to the number of colliders that the Ray hit, but no more than the length of the array it stores its results in.

This is useful, as knowing how many results were actually returned makes it easier to avoid referencing empty elements when the array isn’t full.

Like this:

RaycastHit[] results = new RaycastHit[10];

void Update()
{
    if (Input.GetMouseButtonDown(0))
    {
        FireLaser();
    }
}

void FireLaser()
{
    Ray ray = Camera.main.ViewportPointToRay(new Vector3(0.5f, 0.5f, 0));
    int hits = Physics.RaycastNonAlloc(ray, results);

    for(int i=0; i < hits; i++)
    {
        Destroy(results[i].transform.gameObject);
    }
}

So when would you use Raycast Non-Alloc?

Raycast Non-Alloc is generally a more efficient version of Raycast All.

However… just like Raycast All, Raycast Non-Alloc returns results in an undefined order.

This means that if you try to use Raycast Non-Alloc as a method for limiting the number of Raycast Collisions, for example, you want to build a weapon that fires through up to 3 enemies, you may not get the results you want.

Using Raycast Non-Alloc in this way will return 3 results, but there’s no guarantee that they will be the closest 3 results, even if you sort the Array.

While it might seem like a good idea to use Raycast Non-Alloc to limit collisions for performance purposes, this isn’t really why it’s efficient.

The main benefit of using Raycast Non-Alloc is to avoid repeatedly allocating new arrays, which prevents garbage and improves performance.

So, to use it effectively, you may actually find it’s better to use a large fixed array, one that’s big enough to accommodate the maximum number of results you’re likely to need at any given time, while using function features, such as Layer Masks and max distance, to filter the initial results for performance.

On balance, and depending on the type of results you want to get back, you may find it’s more convenient for you to use Raycast All.

And, in many cases, this will be fine…

However, if you find yourself using it frequently, or you’re calling it from multiple objects, you may be better off using Raycast Non-Alloc instead.

Collider playerCollider;
if (playerCollider.Raycast(Ray ray, out RaycastHit hitData, float maxDistance))
    {
        // Hit the player!
    }

Should you use Raycast in Fixed Update or Update?

In many cases, it’s better to use Raycast in Update, however, this largely depends on what you’re trying to do.

Typically, because Raycast is a Physics function, you might think to put Raycast in Fixed Update, which is called every physics step, instead of Update, which is called every frame.

Fixed Update is designed to perform actions in sync with the physics system, which will often run at a different frequency to Update.

If the game’s framerate is low, then Fixed Update may run faster than Update, being called several times during a frame. However, if the game’s framerate is high, Fixed Update may not be called at all during a frame.

A typical use of Fixed Update is for continuous physics functions. For example, when applying force to a Rigidbody, doing it in Fixed Update means that the force is applied in sync with the physics system that is reacting to it.

However…

While Raycast is a physics function, what you’re doing with it may actually be more suited to Update.

Why?

A lot of the time, you’ll be using Raycast as a check.

For example, was something in the line of fire when I clicked the mouse button?

Was the player close enough to the ground when the jump button was pressed?

Is the player looking at the object they just tried to pickup?

All of these examples are dependent on a player input condition that’s designed to be used Update, and trying to put functions like that in Fixed Update is going to cause problems.

For example, in extreme circumstances where the framerate of the game is slower than the physics system, a click that’s measured on a per-frame basis will be true every time Fixed Update is called during that frame. This would mean that even though you clicked once, the action could be called multiple times.

Whereas, if the physics system is running much slower than the framerate, Fixed Update might not be called while the button is pressed, and the click may not be recognised at all.

Instead, even though Raycast is Physics-based, placing the mouse click condition in Update, where it would normally be, solves this problem:

void Update()
    {
        if (Input.GetMouseButtonDown(0)) 
        { 
            FireLaser();
        }
    }

    void FireLaser()
    {
        Ray ray = new Ray(transform.position, transform.forward);

        if (Physics.Raycast(ray, 10, worldLayer))
        {
            Debug.Log("You shot a wall!");
        }
    }

This works because the Raycast is a one-time event, that’s simply reporting the state of the Physics system at the time of the check.

But what about continuous checks?

There may be times when you’re making constant Raycast calls to check for colliders.

So should they be made from Update, or Fixed Update?

Again, it depends on what you’re trying to do as a result of the Raycast check.

If the resulting action of the continuous check is something you would normally put in Update, then use Update.

This will keep the action in sync with the game’s framerate.

However,

If the resulting action is something you would normally place in Fixed Update, then it’s a good idea to use Fixed Update for the Raycast check and the resulting action.

For example, making an object hover by applying force to a Rigidbody when it gets close to the ground.

Like this: 

public class FloatObject : MonoBehaviour
{
    public Rigidbody rb;

    private void FixedUpdate()
    {
        Ray ray = new Ray(transform.position, Vector3.down);
        if (Physics.Raycast(ray, 2))
        {
            FloatUp();
        }
    }

    void FloatUp()
    {
        Vector3 forceAmount = new Vector3(0, 20, 0);
        rb.AddForce(forceAmount);
    }
}

Both the Raycast check and the hover action are designed to work with Physics steps so, in this scenario, you’ll get more consistent results by using Fixed Update.

How to use Raycast in Unity in 2D

Raycast is a physics-based function, meaning that, depending on which version you use, it derives from either the Physics Class or a related class, such as the Collider Class.

However…

In Unity, the 3D and 2D physics engines are separate, meaning that, if you want to use Raycast in 2D, you’ll need to use a different version of Raycast that derives from the 2D physics engine and its classes. For example, Physics2D.Raycast or Collider2D.Raycast.

Otherwise, it won’t work.

Like this:

void Update()
{
    if (Physics2D.Raycast(transform.position, Vector2.down)) 
    {
        // Something was hit!
    }
    else 
    {
        // Something was not hit!
    }
}

Raycasts in 3D vs Raycasts in 2D

Generally, the 2D versions of Raycast work in a similar way to the standard, 3D versions, but with a few key differences.

For example, while many versions of Raycast return a boolean value (which returns true if the Ray hits something and false if it doesn’t), this isn’t the case with the 2D versions of Raycast.

Instead of returning a boolean, Physics2D.Raycast returns a Raycast Hit 2D value.

If the Raycast hits a collider, the function will return Raycast Hit 2D information. If it doesn’t hit anything, it returns null, which is why it’s still possible to use Physics2D.Raycast in an if condition, even though it doesn’t return a boolean value.

However, this does mean that, unlike the 3D version, where you would normally save hit data using the out keyword, if you want to access information about what was hit, you’ll need to declare a Raycast Hit 2D variable first.

Like this:

private void Update()
{
    RaycastHit2D hitInfo = Physics2D.Raycast(transform.position, Vector2.down);

    if (hitInfo.collider) 
    {
        Debug.Log("Hit " + hitInfo.collider);
    }
    else 
    {
        Debug.Log("Hit nothing!");
    }
}

Collider 2D Raycast ignores its own collider

Just like the 2D version of the standard Raycast function, the 2D version of Collider.Raycast works differently to its 3D counterpart.

Unlike the 3D version of Collider.Raycast, which takes a Ray parameter and looks specifically for the one collider that it’s called from, Collider2D.Raycast fires a ray from the collider it’s called from and looks for other colliders to hit (while ignoring its own).

Collider2D.Raycast has an integer return type, which is equal to the number of colliders that were intersected by the Raycast, storing the results in an array.

Which means, to use Collider2D.Raycast, you’ll need to declare and initialise an array to hold the results.

To create a Raycast Hit 2D array, you’ll need to declare and initialise it in your script. This is because the Raycast Hit 2D data type won’t appear in the Inspector so, unlike other arrays, you won’t be able to set the length of the array manually.

Like this:

RaycastHit2D[] hits = new RaycastHit2D[10];

This will create a new Array with a length of Ten.

The length of the array determines how many Colliders can be counted by the Raycast function.

So, for example, if you initialise the array at ten, even if the ray intersects 12 colliders, the integer value that you get back will be capped at ten.

Like this:

public class CheckGround : MonoBehaviour
{
    public Collider2D playerCollider;
    public int numCollidersHit;
    RaycastHit2D[] hits = new RaycastHit2D[10];

    private void Update()
    {
        numCollidersHit = playerCollider.Raycast(Vector2.down, hits);
    }
}

Collider2D.Raycast works in a similar way to the Non-allocating version of Raycast All. Except that, in 2D, Raycast All Non-Alloc will also detect colliders that overlap the ray’s origin.

Which can be inconvenient if you’re calling the function from an object with a collider that you want to ignore.

Instead, Collider2D.Raycast ignores its own collider and looks for others, without generating any garbage.

This is because it reuses the same fixed array instead of making a new one each time.

There’s also an alternative version of Collider2D.Raycast that stores its results in a List instead of an array:

public class CheckGround : MonoBehaviour
{
    List<RaycastHit2D> hits = new List<RaycastHit2D>();
    public Collider2D playerCollider;
    public ContactFilter2D filter;

    private void Update()
    {
        if(Input.GetMouseButtonDown(0))
        {
            int objectsHit = playerCollider.Raycast(Vector2.down, filter, hits, 10);

            for (int i=0; i < objectsHit; i++)
            {
                // Do something!
            }
        }
    }
}

This is useful when you want to limit the garbage allocation of the Raycast function but you don’t want to place a limit on the number of objects that can be detected, as the List will be resized, but only as needed when the function is called.

The 2D version of Raycast All sorts its results

Unlike the 3D version of Raycast All, which stores results in an undefined order, the 2D version of Raycast All sorts its results by distance from the origin.

This is useful if you want to, for example, destroy objects in a line or affect multiple objects based on their distance from the Ray’s origin, without needing to sort the array.

Use Contact Filters for advanced filtering in 2D

Unlike the 3D version of Raycast, which relies on manually setting a Layer Mask or trigger settings in the function’s parameters, Raycast in 2D allows you to use a Contact Filter 2D parameter to easily include or exclude certain objects from being hit.

It can also be declared publicly, meaning that you can apply the settings you want directly in the Inspector.

Like this:

Contact Filters allow you to set multiple filtering options.

It can then passed into any overload methods of Raycast that support using Contact Filters.

Such as this one:

public class CheckGround : MonoBehaviour
{
    public ContactFilter2D filter;
    RaycastHit2D[] hits = new RaycastHit2D[10];

    void Update()
    {
        if(Input.GetMouseButtonDown(0))
        {
            int objectsHit = Physics2D.Raycast(transform.position, Vector2.down, filter, hits);

            for (int i=0; i < objectsHit; i++)
            {
                Destroy(hits[i].transform.gameObject);
            }
        }
    }
}

If, however, you want to use an overload method of Raycast that requires a Contact Filter, but you don’t actually want to use a Contact Filter, you can do that too.

Simply declare a Contact Filter variable and use the No Filter function to prevent the filter from excluding any results.

Like this:

ContactFilter2D filter;
RaycastHit2D[] hits = new RaycastHit2D[10];

void Update()
{
    int numCollidersHit = Physics2D.Raycast(transform.position, Vector2.down, filter.NoFilter(), hits);
}

Now it’s your turn

Now I want to hear from you…

How are you using Raycasts in Unity?

What’s your best Raycast tip that you know others will find useful?

And how will you use the information on this page in your own project?

Let me know by leaving a comment below.

by John French

Game audio professional and a keen amateur developer.

• YouTube
• johnlfrench
• johnleonardfrench.com

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How this content was created

This article was written using first-hand research and experience, without the use of AI. For more information on how Game Dev Beginner articles are written, see my writing policy.