GeometriCS/intersections/IntersectionLine2ToLineSegment2.cs

namespace GeometriCS
{
    /// <summary>
    /// Intersection between a line and a line segment. Double precision.
    /// </summary>
    public class IntersectionLine2ToLineSegment2d
    {
        /// <summary>
        /// Possible statuses the intersection can be.
        /// </summary>
        public enum Statuses
        {
            /// <summary>
            /// Intersection is valid.
            /// </summary>
            SUCCESS,
            /// <summary>
            /// The two lines are parallel.
            /// </summary>
            PARALLEL,
            /// <summary>
            /// The line segment is colinear with the line.
            /// </summary>
            COLINEAR,
            /// <summary>
            /// The intersection would happen if the intersectors were unbounded, but not inside the bounds.
            /// </summary>
            OUTOFBOUNDS,
        }

        /// <summary>
        /// The intersecting line.
        /// </summary>
        public Line2d Line { get; }

        /// <summary>
        /// The intersecting line segment.
        /// </summary>
        public LineSegment2d LineSegment { get; }

        /// <summary>
        /// Status of the intersection.
        /// </summary>
        public Statuses Status { get; }

        /// <summary>
        /// The point of the intersection between the line and line segment.
        /// </summary>
        public Vector2d? Result { get; }

        /// <summary>
        /// Constructor for Line2d to LinearSegment2d intersection.
        /// </summary>
        /// <param name="line">The intersecting line.</param>
        /// <param name="lineSegment">The intersecting lineSegment.</param>
        public IntersectionLine2ToLineSegment2d(Line2d line, LineSegment2d lineSegment)
        {
            Line = line;
            LineSegment = lineSegment;

            // Construct line coefficients for the linesegment
            (double segment_A, double segment_B, double segment_C) =
                Utils.Line2CoefficientsFromTwoPoints(lineSegment.StartPoint, lineSegment.EndPoint);

            // Check if lines are parallel
            // TODO: Check what happens if coeff_B == 0
            // TODO: Find a non-retarded way to put this into a function so
            //       that it can be reused by all the 2d linear intersections.
            if (Utils.DoubleEquals(line.Coeff_A / line.Coeff_B, segment_A / segment_B))
            {
                // Null result
                Result = null;

                // Check if lines are coincidental
                if (Utils.DoubleEquals(line.Coeff_A / segment_A, line.Coeff_B / segment_B) &&
                    Utils.DoubleEquals(line.Coeff_A / segment_A, line.Coeff_C / segment_C))
                {
                    Status = Statuses.COLINEAR;
                }
                else
                {
                    Status = Statuses.PARALLEL;
                }

                return;
            }

            // Perform the intersection calculation
            double divisor = line.Coeff_A * segment_B - segment_A * line.Coeff_B;
            double x0 = (line.Coeff_B * segment_C - segment_B * line.Coeff_C) / divisor;
            double y0 = (line.Coeff_C * segment_A - segment_C * line.Coeff_A) / divisor;
            Result = new Vector2d(x0, y0);

            // Check if result is inside of the segment.
            if (lineSegment.Extents.Contains((Vector2d)Result))
            {
                Status = Statuses.SUCCESS;
            }
            else
            {
                Status = Statuses.OUTOFBOUNDS;
            }
        }
    }
}