Correctly calculate bounding box for a transformed rectangle with System.Numerics

Question

I'm using the following algorithm to calculate the bounding box for a transformed rectangle but it seems to have issues.

public static Rectangle GetBoundingRectangle(Rectangle rectangle, Matrix3x2 matrix)
{
    Vector2 leftTop = Vector2.Transform(new Vector2(rectangle.Left, rectangle.Top), matrix);
    Vector2 rightTop = Vector2.Transform(new Vector2(rectangle.Right, rectangle.Top), matrix);
    Vector2 leftBottom = Vector2.Transform(new Vector2(rectangle.Left, rectangle.Bottom), matrix);
    Vector2 rightBottom = Vector2.Transform(new Vector2(rectangle.Right, rectangle.Bottom), matrix);

    Vector2 min = Vector2.Min(Vector2.Min(leftTop, rightTop), Vector2.Min(leftBottom, rightBottom));
    Vector2 max = Vector2.Max(Vector2.Max(leftTop, rightTop), Vector2.Max(leftBottom, rightBottom));

    return new Rectangle(0, 0, (int)(max.X - min.X), (int)(max.Y - min.Y));
}

It works well with rotation but not with skew. As you will can see from the images below the rectangle calculated from the formula is too small. Can anyone spot what the issue is or is there a method already within the System.Numerics namespace that I can use?

Rotate - Matrix formula

Matrix3x2.CreateRotation(radians, origin)

Skew - Matrix formula

Matrix3x2.CreateRotation(radiansX, radiansY, origin)

Answer 1

I'm not sure exactly what the problem is with what you've done but it isn't representing the most robust definition of the bounding box which is this:

var allCorners = new List<Vector2> { leftTop, rightTop, leftBottom, rightBottom };
var xExtent = allCorners.Select(v => v.X).Max() - allCorners.Select(v => v.X).Min();
var yExtent = allCorners.Select(v => v.Y).Max() - allCorners.Select(v => v.Y).Min();
return new Rectangle(0, 0, xExtent, yExtent);