CODEWITHSUNDEEP
c#xnapointintersect
Ben
Ben

Reputation: 1349

How do I check if a Rectangle overlaps the area between three Points? (C# and XNA)

I am making a game in C# and XNA and I am using three Points to represent the hitbox of an enemy object. A Rectangle variable is used to represent the player's hitbox. I am using three Points for the enemy rather than a rectangle as the enemy is shaped like a triangle.

//Example coordinates
Point pointOne = new Point(0, 50);
Point pointTwo = new Point(50, 50);
Point pointThree = new Point(25, 0);
Rectangle rect = new Rectangle(0, 0, 10, 10);

I need a way to determine if the Rectangle overlaps the area between all of the Points, as shown in the following pictures. Would anybody be able to show me a method or some kind of code that could help me accomplish this?

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Upvotes: 2

Views: 549

Answers (1)

Steve H
Steve H

Reputation: 5519

Here is an alternative implementation:

class Triangle
{
    Vector2 topPoint, rightPoint, leftPoint;


    public Triangle(Vector2 p1, Vector2 p2, Vector2 p3)
    {
        topPoint = p1;
        rightPoint = p2;
        leftPoint = p3;
    }



    public bool IsRectIntersecting(List<Vector2> corners)//corners are the corners of the polygon being tested
    {


        if (AreAnyOfTheCornesInsideTriangleLineSegment(topPoint, rightPoint, corners) && 
            AreAnyOfTheCornesInsideTriangleLineSegment(rightPoint, leftPoint, corners) && 
            AreAnyOfTheCornesInsideTriangleLineSegment(leftPoint, topPoint, corners))
        {
            return true;
        }

        return false;
    }

    private bool AreAnyOfTheCornesInsideTriangleLineSegment(Vector2 pointA, Vector2 pointB, List<Vector2> corners)
    {
        Vector2 lineSegment = pointA - pointB;
        Vector3 lineSegment3D = new Vector3(lineSegment, 0);
        Vector3 normal3D = Vector3.Cross(lineSegment3D, Vector3.UnitZ);
        Vector2 normal = new Vector2(normal3D.X, normal3D.Y);

        foreach (Vector2 corner in corners)
        {
            if (Vector2.Dot(normal, corner - pointB) < 0)
            {
                return true;
            }
        }

        return false;
    }
}

Upvotes: 2

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