RectangleIntersection.cs

using System;

namespace Advanced.Algorithms.Geometry;

/// <summary>
///     Rectangle intersection finder.
/// </summary>
public class RectangleIntersection
{
    /// <summary>
    ///     Returns the rectangle formed by the intersection if do intersect.
    ///     Otherwise default value of Rectangle struct.
    /// </summary>
    public static Rectangle FindIntersection(Rectangle a, Rectangle b)
    {
        //check for intersection
        if (!DoIntersect(a, b))
            //no intersection
            return null;

        var leftTopCorner = new Point
        (
            Math.Max(a.LeftTop.X, b.LeftTop.X),
            Math.Min(a.LeftTop.Y, b.LeftTop.Y)
        );


        var rightBottomCorner = new Point
        (
            Math.Min(a.RightBottom.X, b.RightBottom.X),
            Math.Max(a.RightBottom.Y, b.RightBottom.Y)
        );


        return new Rectangle
        {
            LeftTop = leftTopCorner,
            RightBottom = rightBottomCorner
        };
    }

    public static bool DoIntersect(Rectangle a, Rectangle b)
    {
        //check for intersection
        if (a.LeftTop.X > b.RightBottom.X // A is right of B   
            || a.RightBottom.X < b.LeftTop.X // A is left of B
            || a.RightBottom.Y > b.LeftTop.Y //A is above B
            || a.LeftTop.Y < b.RightBottom.Y) //A is below B
            //no intersection
            return false;

        return true;
    }
}