Issues using Physics2D.Linecast for Movement Collision

Question

It's quite possible I'm missing something obvious (I'm still rather new to this) despite checking the documentation, but I'm at my wit's end with this issue.

I'm attempting to add simple linecast collisions to my 2D movement system that checks if there's a wall on the relevant layer to disallow movement, but I cannot get the distance parameter to function properly. It's responding as if my distance is set to the default MathF.Infinity, despite me feeding a float variable into it.

Furthermore, unity keeps giving me this error after I moved my layermask declaration into the Start function: "The name 'mask' does not exist in the current context." I'm unsure why this is happening.

Here's the relevant code:

float distance = 1f;

void Start()
{
    LayerMask mask = LayerMask.GetMask("BlockingLayer");

}
void FixedUpdate()
{
    // Move up IF !isMoving and No collision detected.
    if (Input.GetKey(KeyCode.W) && !isMoving && Physics2D.Linecast(transform.position, Vector2.up, mask, distance))
            StartCoroutine(MovePlayer(Vector2.up));
}

Alright, after working with the helpful people responding, I've updated my code. Unfortunately, my issue seems to have inverted. Rather than detecting collision always, collision does not seem to be detected ever. Here's the new code (Edited to reflect small change):

    float maxDistance = 2f;
RaycastHit2D hitU;

void FixedUpdate()
{
     hitU = Physics2D.Raycast(transform.position, Vector2.up, LayerMask.GetMask("BlockingLayer"));
    // Move up IF !isMoving and No collision detected.
    if ((hitU.collider != null && (hitU.distance < maxDistance)))
    {
        if (Input.GetKey(KeyCode.W) && !isMoving)
        {
            StartCoroutine(MovePlayer(Vector2.up));
            Debug.DrawRay(transform.position, Vector2.up, Color.red);
        }

    }

Answer 1

Distance param

I think you're confusing the parameters for Physics2D.Raycast with Physics2D.LineCast. The "distance" parameter your passing into Physics2D.LineCast is actually a "minDepth" value. Which according to Unity Docs:

Only include objects with a Z coordinate (depth) greater than or equal to this value.

Which means it actually has nothing to do with distance in 2D space, but rather rather operates on the z-axis.

Solution

I would employ Physics2D.Raycast instead. The tricky "gotcha" with this method (at least in 3D), is that the distance param is actually just used by the Unity engine to optimize the raycasting algorithm so unity doesn't do more intersection tests than it has to. It isn't a guarantee for the precise max distance that the raycast hits will return.

You'll have to perform these checks yourself to be sure:

var hit = Physics2D.Raycast(transform.position, Vector2.up);

//if there was a hit, and distance was less than maxdist...
if ((hit.collider != null && (hit.distance < maxDistance))
{
   //do....
}

---

"The name 'mask' does not exist in the current context."

This is happening because your mask variable goes out of scope at the end of the your Start() method. You have to declare your mask variable as a member variable, so it's lifetime matches the lifetime of your script.

Try this instead:

LayerMask mask;

void Start()
{
    mask = LayerMask.GetMask("BlockingLayer");
}
```