How can I prevent clicks from going through a GUI.Box?

Question

I have a GUI.Box that I slide in from the side of the screen. How can I prevent mouse interaction from going to any objects under it (another GUI.Button for instance, or for that matter an GameObject)?

Answer 1

This is one of the annoying limitations of the built-in version of Unity's GUI. From most accounts I've seen, you have to do it yourself. Write an input manager that checks locations of mouse clicks and then decides to forward or not the clicks to whatever game systems you want.

Alternatively, use a different kind of input system that is based off of colliders. A popular one is NGUI.

Answer 2

This could be done fairly simply and elegantly with GUI.depth and styling a GUI button as a box.

void OnGUI()
{
    int prevDepth = GUI.depth;
    GUI.depth = 0;
    if(GUI.Button(someRect, "Some Button","Box"))
    {
        // Do something
        Event.current.Use();
    }
    GUI.depth++;
    // Do other stuff
    GUI.depth = prevDepth;
}

Answer 3

If we have lots of objects in a scene it's often preferable to use a single script that handles the click Raycast itself instead of every collider object also having an void OnMouseDown() callback.

When performing the Raycast ourselves we can check GUIUtility.hotControl to see if an IMGUI UI control was just clicked.

Here is an example that performs such a raycast on an arbitrary number of collider objects in the scene and handles both having mouse clicks be blocked by Immediate Mode UI as well as Canvas-based UI (just for good measure).

Here is the source code: https://gist.github.com/JohannesMP/3d3882e6bd57e378412fa5d7d95d0c47