指定するスクリーン座標に GUI 要素があるか確認します。
Returns true if the screenPosition
is contained in this GUIElement. screenPosition
is specified in
screen coordinates, like the values returned by the Input.mousePosition property.
If no camera
is given a camera filling the entire game window will be assumed.
Note that if the position is inside the element, true
will be returned even if
the game object belongs to Ignore Raycast layer (normally mouse events are not sent
to Ignore Raycast objects).
See Also: GUILayer.HitTest.