使用2D Raycast来检测对象对撞机上的鼠标悬停时的问题

Question

Im currently working on a 2D character selection screen in Unity that should operate similarly to the Mortal Kombat character selection screen. Currently, I have a class called CharacterSelector attached to the main camera. The class holds methods for selection/deselection of characters, hover events, and selection confirmation. I was able to use a RayCast2D to build my character selection method; however, I am running into issues using it for hover events.

In my scene, I have a group of character images that the player can choose from (if they are unlocked). When the player hovers over the character with his/her mouse, the character image should be surrounded by a yellow border. When the user clicks on the desired character, a larger version of the image will popup to the left of the character image group.

Right now, I have the following code for the hover method:

    public void onHover(Ray ray, RaycastHit2D hit)
    {
        if(hit.collider == null)
        {
            Debug.Log("nothing hit");

        }            
        if (Physics2D.Raycast(ray.origin, ray.direction, Mathf.Infinity))
        {
            print(hit.collider.name);
        }
    }

This method belongs to a class that the CharacterSelection class inherits from. The following is on the CharacterSelection class:

class CharacterSelector : Selector
{
    Ray ray;
    RaycastHit2D hit;        

    public void Start()
    {
        ray = Camera.main.ScreenPointToRay(Input.mousePosition);
    }

    void Update()
    {
        onHover(ray, hit); 

        if (Input.GetMouseButtonDown(0))
        {                               
            selectCharacter();
        }
    }                   
}

Also, all the character images that I am trying to hover over currently have 2D Box Colliders. As of right now, I am unable to get hover operation to work. It does not print the name of the character image to the console. I am using this as a first step to see if Unity recognizes the character image or not. Let me know if I can provide additional information!

Answer 1

Mouse changes position on screen almost every frame. This means your ray should be updated every frame according to mouse position. So I moved the corresponding statement from Start() to Update();

class CharacterSelector : Selector
{
    Ray ray;    
    RaycastHit2D hit;   

    public void Start()
    {

    }

    void Update()
    {
        ray = Camera.main.ScreenPointToRay(Input.mousePosition);
        onHover(ray, hit); 

        if (Input.GetMouseButtonDown(0))
        {                               
            selectCharacter();
        }
    }                   
}

Secondly, if you look in the definition of Physics2D.Raycast you'll find that it gives you back the RaycastHit2D object. This is the object you should check the collider of, not your hit object which should have thrown an NullReferenceException, I don't know why it didn't. So this:

public void onHover(Ray ray, RaycastHit2D hit)
{
    hit = Physics2D.Raycast(ray.origin, ray.direction, Mathf.Infinity);
    if(hit.collider == null)
    {
        Debug.Log("nothing hit");

    }            
    else
    {
        print(hit.collider.name);
    }
}

Apart from this you don't really need the hit argument in onHover() function, it can be a local variable in the function. But if you are planning on using your hit variable in CharacterSelector script than you should change the declaration of onHover to: onHover(Ray ray, out RaycastHit2D hit) the out keyword passes the variable by reference instead of a copy of its value.

Also, I think checking if mouse is hovering over an object shouldn't be done in onHover, it's kinda misleading and doesn't seem logical to me. I'd move the body of onHover to another function like RaycastChecker(). I'd call onHover() only if mouse is actually hovering over the sprite. (like in OnCollisionEnter you take it granted that the collision did happen, so should the onHover, I think)