Localizing OnMouseDown() to a GameObject in Unity

 Localizing OnMouseDown() to a GameObject in Unity

Unity's OnMouseDown() callback detects mouse clicks globally. However, you often want to detect clicks on a specific gameObject rather than any object. Here are two ways to localize OnMouseDown() to a particular gameObject:

Using Buttons and UI

For UI elements, use the Button component which has onClick events. These are localized to the button gameObject.

For example:

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public Button myButton;

public void HandleMyButtonClick() {
  //Clicked!
}

void Start() {
  myButton.onClick.AddListener(HandleMyButtonClick); 
}

Raycasting from Camera 

For non-UI gameObjects, use a PhysicsRaycaster and raycast from the mouse position to detect hits.

For example: 

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void Update() {
  if(Input.GetMouseButtonDown(0)) {
   
    Ray ray = camera.ScreenPointToRay(Input.mousePosition);  

    if(Physics.Raycast(ray, out RaycastHit hit)) {
      if(hit.collider.gameObject == myObject) {
        //Clicked myObject
      } 
    }
  }
}

This will detect if the mouse is over the specific object when clicked.

Localizing input events is useful to isolate interactions and respond to clicks on specific gameObjects. Using raycasting or button components achieves this in different situations.