Click through

It's very common to have game world objects which can be clicked/ tapped on. However, if your UI is over one of those objects, you might get something called 'click through' - where both the UI and your game world object handle the click.

Why click through happens

Unity doesn't provide a way to block the built in raycast which occurs when the screen is pressed or the mouse is clicked. Click through happens for Unity's built in GUI too. So, because PowerUI can't block it from happening, both Unity's raycast and PowerUI's element resolve occur at the same time - when both happen to get handled, then the click through scenario arises.

Avoiding it

Unity GUI and older versions of PowerUI have a flag which you check from your MonoBehaviour click methods (like OnMouseDown). Due to a wider variety of events (e.g. the touch events) and as PowerUI fully supports multi-touch (which the flag route fails for), there's now two potential routes - both involve catching the event after they've passed through the UI:

Use Input.Unhandled

See also the event flow. This special EventTarget receives all events which were not handled by your UI. If you click 'through' your UI, the mouse/touch events are sent here. Grab them using addEventListener:

PowerUI.Input.Unhandled.addEventListener("mousedown",delegate(MouseEvent e){
    
    // They clicked on *nothing!* (straight 'through' the UI).
    // Send this event wherever you'd like.
    // Note that the original raycast (and any GameObject it hit) are available:
    if(e.raySuccess){
        // It hit something! Use rayHit next.

        // Get the clicked gameObject:
        GameObject go = e.rayHit.gameObject;
        
        // Try getting a MonoBehaviour called 'MyInputScript':
        MyInputScript myInput = go.GetComponent<MyInputScript>();
        
        if(myInput != null){
            // Great - forward the event to it:
            myInput.MouseDown(e);
        }
    }
    
});

PowerUI tries to give your input system as much flexibility as possible, so the above route is considered relatively low level and which allows you to pipe those events wherever you need them, but requires a little more scripting to hook it up.

Setup an EventTarget MonoBehaviour

This is the easier route, but involves PowerUI defining more of your input system. This also has the advantage of being able to correctly handle 3D context menu's too. Firstly, add something like the following to your project:

Design notes: This script will probably be built in. See the 'alternative design' section below.

using UnityEngine;
using System.Collections;
using PowerUI;
using Dom;


// First make it a Dom.IEventTarget:
public class GameObjectEventTarget : MonoBehaviour,IEventTarget {
    
    // An underlying event target which allows us to addEventListener etc:
    public EventTarget Target = new EventTarget();
    
    // IEventTarget requires the dispatchEvent method.
    // It's the same as the standard W3C dispatchEvent.
    // Define that too:
    public bool dispatchEvent(Dom.Event e){
    
        // We received some event!
        // This typically happens when the UI did not handle it, 
        // or because an event was specifically dispatched to this gameObject.
        return Target.dispatchEvent(e);
    
    }
    
}

// Extend GameObject with a 'GetEventTarget' method.
public static class GameObjectExtensions{
 
    /// <summary>Gets or creates an EventTarget on a GameObject.</summary>
    public static EventTarget getEventTarget(this GameObject go){
        // Get the monobehaviour:
        GameObjectEventTarget monoBehaviour = go.GetComponent<GameObjectEventTarget>();
       
        if(monoBehaviour == null){
            // Add it:
            monoBehaviour = go.AddComponent<GameObjectEventTarget>();
        }
        
        // Return the target property:
        return monoBehaviour.Target;
    }

    /// <summary>Dispatches an event to a gameObject.
    /// Depending on the events settings, it may bubble up the scene hierarchy.</summary>
    public static bool dispatchEvent(this GameObject go, Dom.Event e){
        // Get the monobehaviour:
        GameObjectEventTarget monoBehaviour = go.GetComponent<GameObjectEventTarget>();
        
        if(monoBehaviour != null){
            monoBehaviour.dispatchEvent(e);
        }
        
        if(e.bubbles && !e.cancelBubble){
            // Bubble to the parent GO:
            Transform parent = go.transform.parent;
            
            if(parent!=null){
                return dispatchEvent(parent.gameObject, e);
            }
        }
        
        return !e.defaultPrevented;
    }
}

Next, to use the above, simply use getEventTarget from within your MonoBehaviour:

public class MyGameworldEvents : MonoBehaviour{
    
    public void Awake(){
        // Get the event target:
        var target = gameObject.getEventTarget();
        
        // Now we're getting somewhere interesting!
        
        // Add a mouse down event (referencing the method name):
        target.addEventListener("mousedown",OnMouseDown);

        // It works with whatever event type you support
        // (see also 'Custom events' in the Event Flow wiki).
        // Inline delegates are fine too:
        target.addEventListener("mouseup",delegate(MouseEvent e){

            // Mouse up.
        });
        
    }

    public void OnMouseDown(MouseEvent e){
    
        // This runs when this gameobject got clicked on
        // and the UI was not.
        
    }
  
}

This way you can dispatch any event to any gameObject too:

// Create whatever event type you'd like:
MissionEvent e= new MissionEvent("missioncomplete");

// Dispatch it to a gameobject:
aGameObject.dispatchEvent(e);

Alternative design

PowerUI could use reflection like Unity does to look for OnMouseDown(MouseEvent e) and similar methods so your scripts could be like this instead:

public class MyGameworldEvents : MonoBehaviour{
    
    [Handle("mousedown")]
    public void OnMouseDown(MouseEvent e){
    
        // This runs when this gameobject got clicked on
        // and the UI was not.
        
    }
  
}

The bonus being it would easily work with all of your custom events too:

public class MyGameworldEvents : MonoBehaviour{
    
    [Handle("missioncomplete")]
    public void OnMissionComplete(MissionEvent e){
        // A mission was completed
        // and the event was dispatched to this gameObject.
    }
  
}

It would then collect those handlers whenever an event is first dispatched to a gameObject, which should ultimately be only a small amount of extra overhead for more convenience. Any opinions?