ImageSharp/PolygonClipper/SweepEvent.cs

// Copyright (c) Six Labors.
// Licensed under the Six Labors Split License.

#nullable disable

using System.Runtime.CompilerServices;

namespace SixLabors.PolygonClipper {
  /// <summary>
  /// Represents a sweep.
  /// </summary>
  internal sealed class SweepEvent
  {
      /// <summary>
      /// Initializes a new instance of the <see cref="SweepEvent"/> class.
      /// </summary>
      /// <param name="point">The point associated with the event.</param>
      /// <param name="left">Whether the point is the left endpoint of the segment.</param>
      /// <param name="otherEvent">The event associated with the other endpoint of the segment.</param>
      /// <param name="polygonType">The polygon type to which the segment belongs.</param>
      /// <param name="edgeType">The type of the edge. Default is <see cref="EdgeType.Normal"/>.</param>
      public SweepEvent(
          Vertex point,
          bool left,
          SweepEvent otherEvent,
          PolygonType polygonType = PolygonType.Subject,
          EdgeType edgeType = EdgeType.Normal)
      {
          this.Point = point;
          this.Left = left;
          this.OtherEvent = otherEvent;
          this.PolygonType = polygonType;
          this.EdgeType = edgeType;
      }

      /// <summary>
      /// Initializes a new instance of the <see cref="SweepEvent"/> class.
      /// </summary>
      /// <param name="point">The point associated with the event.</param>
      /// <param name="left">Whether the point is the left endpoint of the segment.</param>
      /// <param name="polygonType">The polygon type to which the segment belongs.</param>
      public SweepEvent(Vertex point, bool left, PolygonType polygonType = PolygonType.Subject)
      {
          this.Point = point;
          this.Left = left;
          this.PolygonType = polygonType;
          this.EdgeType = EdgeType.Normal;
      }

      /// <summary>
      /// Initializes a new instance of the <see cref="SweepEvent"/> class.
      /// </summary>
      /// <param name="point">The point associated with the event.</param>
      /// <param name="left">Whether the point is the left endpoint of the segment.</param>
      /// <param name="contourId">The ID of the contour to which the event belongs.</param>
      public SweepEvent(Vertex point, bool left, int contourId)
      {
          this.Point = point;
          this.Left = left;
          this.ContourId = contourId;
          this.PolygonType = PolygonType.Subject;
          this.EdgeType = EdgeType.Normal;
      }

      /// <summary>
      /// Gets the point associated with the event.
      /// </summary>
      public Vertex Point { get; }

      /// <summary>
      /// Gets or sets a value indicating whether the point is the
      /// left (source) endpoint of the segment (p, other->p).
      /// </summary>
      public bool Left { get; set; }

      /// <summary>
      /// Gets or sets the ID of the contour to which the event belongs.
      /// </summary>
      public int ContourId { get; set; }

      /// <summary>
      /// Gets index of the polygon to which the associated segment belongs to;
      /// </summary>
      public PolygonType PolygonType { get; }

      /// <summary>
      /// Gets or sets the type of the edge.
      /// </summary>
      public EdgeType EdgeType { get; set; }

      /// <summary>
      /// Gets or sets the event associated to the other endpoint of the segment.
      /// </summary>
      public SweepEvent OtherEvent { get; set; }

      /// <summary>
      /// Gets or sets a value indicating whether the segment (p, other->p) represent an
      /// inside-outside transition in the polygon for a vertical ray from (p.x, -infinite)
      /// that crosses the segment.
      /// </summary>
      public bool InOut { get; set; }

      /// <summary>
      /// Gets or sets a value indicating whether the inOut transition for the segment from
      /// the other polygon preceding this segment in the sweep line.
      /// </summary>
      public bool OtherInOut { get; set; }

      /// <summary>
      /// Gets or sets the sorted sweep events. Only used in "left" events.
      /// Position of the event (segment) in SL (status line).
      /// </summary>
      public int PosSL { get; set; }

      /// <summary>
      /// Gets or sets the previous segment in the sweep line  belonging to the result of the
      /// boolean operation.
      /// </summary>
      public SweepEvent PrevInResult { get; set; }

      /// <summary>
      /// Gets or sets the transition state of the event in the result.
      /// </summary>
      public ResultTransition ResultTransition { get; set; }

      /// <summary>
      /// Gets a value indicating whether the event contributes to the result.
      /// </summary>
      public bool InResult => this.ResultTransition != ResultTransition.Neutral;

      /// <summary>
      /// Gets or sets the position of the event in the sorted events.
      /// </summary>
      public int Pos { get; set; }

      /// <summary>
      /// Gets or sets a value indicating whether the event is a result in-out transition.
      /// </summary>
      public bool ResultInOut { get; set; }

      /// <summary>
      /// Gets or sets the output contour ID associated with this contour.
      /// </summary>
      public int OutputContourId { get; set; }

      /// <summary>
      /// Is the line segment (point, otherEvent->point) below point p.
      /// </summary>
      /// <param name="p">The point to check against.</param>
      /// <returns>
      /// <see langword="true"/> if the line segment is below the point; otherwise <see langword="false"/>.
      /// </returns>
      [MethodImpl(MethodImplOptions.AggressiveInlining)]
      public bool IsBelow(in Vertex p)
          => this.Left
          ? PolygonUtilities.SignedArea(this.Point, this.OtherEvent.Point, p) > 0D
          : PolygonUtilities.SignedArea(this.OtherEvent.Point, this.Point, p) > 0D;

      /// <summary>
      /// Is the line segment (point, otherEvent->point) above point p.
      /// </summary>
      /// <param name="p">The point to check against.</param>
      /// <returns>
      /// <see langword="true"/> if the line segment is above the point; otherwise <see langword="false"/>.
      /// </returns>
      [MethodImpl(MethodImplOptions.AggressiveInlining)]
      public bool IsAbove(in Vertex p) => !this.IsBelow(p);

      /// <summary>
      /// Is the line segment (point, otherEvent->point) a vertical line segment.
      /// </summary>
      /// <returns>
      /// <see langword="true"/> if the line segment is vertical; otherwise <see langword="false"/>.
      /// </returns>
      [MethodImpl(MethodImplOptions.AggressiveInlining)]
      public bool IsVertical() => this.Point.X == this.OtherEvent.Point.X;

      /// <summary>
      /// Determines if this sweep event comes before another sweep event.
      /// </summary>
      /// <param name="other">The other sweep event to compare with.</param>
      /// <returns>
      /// <see langword="true"/> if this event comes before the other; otherwise <see langword="false"/>.
      /// </returns>
      [MethodImpl(MethodImplOptions.AggressiveInlining)]
      public bool IsBefore(SweepEvent other)
      {
          // Compare by x-coordinate first
          if (this.Point.X != other.Point.X)
          {
              return this.Point.X < other.Point.X;
          }

          // If x-coordinates are equal, compare by y-coordinate
          return this.Point.Y < other.Point.Y;
      }

      /// <summary>
      /// Returns the segment associated with the sweep event.
      /// </summary>
      /// <returns>The <see cref="Segment"/>.</returns>
      [MethodImpl(MethodImplOptions.AggressiveInlining)]
      public Segment GetSegment() => new(this.Point, this.OtherEvent.Point);
  }
}