ImageSharp/PolygonClipper/OutputRecord.cs

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

using System.Collections.Generic;

namespace SixLabors.PolygonClipper {
  /// <summary>
  /// Captures a clipped contour, its topology, and its ownership hierarchy.
  /// </summary>
  internal sealed class OutputRecord
  {
      /// <summary>
      /// Gets or sets the stable index assigned when the record is pooled.
      /// </summary>
      public int Index { get; set; }

      /// <summary>
      /// Gets or sets the number of output points in the contour.
      /// </summary>
      public int OutputPointCount { get; set; }

      /// <summary>
      /// Gets or sets the containing output record, if any.
      /// </summary>
      public OutputRecord? Owner { get; set; }

      /// <summary>
      /// Gets or sets the front edge that defines the output orientation.
      /// </summary>
      public ActiveEdge? FrontEdge { get; set; }

      /// <summary>
      /// Gets or sets the back edge that defines the output orientation.
      /// </summary>
      public ActiveEdge? BackEdge { get; set; }

      /// <summary>
      /// Gets or sets the circular linked list of output points.
      /// </summary>
      public OutputPoint? Points { get; set; }

      /// <summary>
      /// Gets or sets the cached bounds for ownership tests.
      /// </summary>
      public Box2 Bounds { get; set; }

      /// <summary>
      /// Gets or sets the temporary contour used during bounds checks.
      /// </summary>
      public List<Vertex> Path { get; set; } = [];

      /// <summary>
      /// Gets or sets split indices used to resolve complex self-intersections.
      /// </summary>
      public List<int>? Splits { get; set; }

      /// <summary>
      /// Gets or sets the cached split ownership used to avoid recursion.
      /// </summary>
      public OutputRecord? RecursiveSplit { get; set; }
  }

  /// <summary>
  /// Represents a vertex in the output contour linked list.
  /// </summary>
  internal sealed class OutputPoint
  {
#pragma warning disable SA1401 // Hot output ring traversal uses fields to avoid accessor overhead.
      /// <summary>
      /// The vertex coordinate.
      /// </summary>
      public Vertex Point;

      /// <summary>
      /// The next point in the linked list.
      /// </summary>
      public OutputPoint? Next;

      /// <summary>
      /// The previous point in the linked list.
      /// </summary>
      public OutputPoint Prev;

      /// <summary>
      /// The owning output record.
      /// </summary>
      public OutputRecord OutputRecord;

      /// <summary>
      /// The horizontal segment reference used for joins.
      /// </summary>
      public HorizontalSegment? HorizontalSegment;
#pragma warning restore SA1401

      /// <summary>
      /// Initializes a new instance of the <see cref="OutputPoint"/> class.
      /// </summary>
      public OutputPoint(Vertex point, OutputRecord outputRecord)
      {
          this.Point = point;
          this.OutputRecord = outputRecord;
          this.Next = this;
          this.Prev = this;
          this.HorizontalSegment = null;
      }
  }

  /// <summary>
  /// Captures a pending horizontal segment to be joined.
  /// </summary>
  internal sealed class HorizontalSegment
  {
      /// <summary>
      /// Initializes a new instance of the <see cref="HorizontalSegment"/> class.
      /// </summary>
      public HorizontalSegment(OutputPoint op)
      {
          this.LeftPoint = op;
          this.RightPoint = null;
          this.LeftToRight = true;
      }

      /// <summary>
      /// Gets or sets the left-most point of the segment.
      /// </summary>
      public OutputPoint? LeftPoint { get; set; }

      /// <summary>
      /// Gets or sets the right-most point of the segment.
      /// </summary>
      public OutputPoint? RightPoint { get; set; }

      /// <summary>
      /// Gets or sets a value indicating whether the segment runs left-to-right.
      /// </summary>
      public bool LeftToRight { get; set; }
  }

  /// <summary>
  /// Stores a pair of horizontal edges to be joined.
  /// </summary>
  internal sealed class HorizontalJoin
  {
      /// <summary>
      /// Initializes a new instance of the <see cref="HorizontalJoin"/> class.
      /// </summary>
      public HorizontalJoin(OutputPoint leftToRight, OutputPoint rightToLeft)
      {
          this.LeftToRight = leftToRight;
          this.RightToLeft = rightToLeft;
      }

      /// <summary>
      /// Gets or sets the left-to-right point of the join.
      /// </summary>
      public OutputPoint? LeftToRight { get; set; }

      /// <summary>
      /// Gets or sets the right-to-left point of the join.
      /// </summary>
      public OutputPoint? RightToLeft { get; set; }
  }
}