UIOverlapChecker.cs

using JetBrains.Annotations;
using UnityEngine;

namespace Kogane
{
    public static class UIOverlapChecker
    {
        private static readonly Vector3[] CORNERS = new Vector3[ 4 ];

        public static bool IsOverlapping
        (
            [NotNull] this RectTransform self,
            [NotNull]      RectTransform rectTransform,
            [CanBeNull]    Camera        camera = null
        )
        {
            if ( self == null ) return false;
            if ( rectTransform == null ) return false;

            var screenRect1 = GetScreenRect( self, camera );
            var screenRect2 = GetScreenRect( rectTransform, camera );

            return screenRect1.Overlaps( screenRect2 );
        }

        private static Rect GetScreenRect
        (
            [NotNull]   RectTransform rectTransform,
            [CanBeNull] Camera        camera
        )
        {
            rectTransform.GetWorldCorners( CORNERS );

            var bottomLeft = RectTransformUtility.WorldToScreenPoint( camera, CORNERS[ 0 ] );
            var topRight   = RectTransformUtility.WorldToScreenPoint( camera, CORNERS[ 2 ] );
            var width      = topRight.x - bottomLeft.x;
            var height     = topRight.y - bottomLeft.y;

            return new Rect
            (
                x: bottomLeft.x,
                y: bottomLeft.y,
                width: width,
                height: height
            );
        }
    }
}