ImageSharp/ImageSharp.Drawing/Processing/Backends/StrokePolylineCommand.cs

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

using System;
using System.Numerics;

namespace SixLabors.ImageSharp.Drawing.Processing.Backends {
  /// <summary>
  /// One explicit stroked open polyline command queued by the canvas batcher.
  /// </summary>
  public readonly struct StrokePolylineCommand
  {
      private readonly PointF[] sourcePoints;
      private readonly DrawingOptions drawingOptions;

      /// <summary>
      /// Initializes a new instance of the <see cref="StrokePolylineCommand"/> struct.
      /// </summary>
      /// <param name="sourcePoints">The source polyline points.</param>
      /// <param name="brush">The brush used to shade the stroke.</param>
      /// <param name="drawingOptions">The drawing options (graphics, shape, transform) used during composition.</param>
      /// <param name="rasterizerOptions">The rasterizer options used to generate coverage.</param>
      /// <param name="targetBounds">The absolute bounds of the logical target.</param>
      /// <param name="destinationOffset">The absolute destination offset of the command.</param>
      /// <param name="pen">The stroke metadata.</param>
      /// <param name="isInsideLayer">True if the command was recorded inside a layer.</param>
      public StrokePolylineCommand(
          PointF[] sourcePoints,
          Brush brush,
          DrawingOptions drawingOptions,
          in RasterizerOptions rasterizerOptions,
          Rectangle targetBounds,
          Point destinationOffset,
          Pen pen,
          bool isInsideLayer)
      {
          ArgumentNullException.ThrowIfNull(sourcePoints);
          if (sourcePoints.Length < 2)
          {
              throw new ArgumentOutOfRangeException(nameof(sourcePoints), "Open stroke polylines require at least two points.");
          }

          this.sourcePoints = sourcePoints;
          this.drawingOptions = drawingOptions;
          this.Brush = brush;
          this.RasterizerOptions = rasterizerOptions;
          this.TargetBounds = targetBounds;
          this.DestinationOffset = destinationOffset;
          this.Pen = pen;
          this.IsInsideLayer = isInsideLayer;
      }

      /// <summary>
      /// Gets the brush used during composition.
      /// </summary>
      public Brush Brush { get; }

      /// <summary>
      /// Gets the drawing options carried by the command.
      /// </summary>
      public DrawingOptions DrawingOptions => this.drawingOptions;

      /// <summary>
      /// Gets the graphics options used during composition.
      /// </summary>
      public GraphicsOptions GraphicsOptions => this.drawingOptions.GraphicsOptions;

      /// <summary>
      /// Gets the rasterizer options used to generate coverage.
      /// </summary>
      public RasterizerOptions RasterizerOptions { get; }

      /// <summary>
      /// Gets the absolute bounds of the logical target for this command.
      /// </summary>
      public Rectangle TargetBounds { get; }

      /// <summary>
      /// Gets the absolute destination offset where the local coverage should be composited.
      /// </summary>
      public Point DestinationOffset { get; }

      /// <summary>
      /// Gets the stroke metadata for this command.
      /// </summary>
      public Pen Pen { get; }

      /// <summary>
      /// Gets the source polyline points.
      /// </summary>
      public PointF[] SourcePoints => this.sourcePoints;

      /// <summary>
      /// Gets the command transform.
      /// </summary>
      public Matrix4x4 Transform => this.drawingOptions.Transform;

      /// <summary>
      /// Gets a value indicating whether the command was recorded inside a layer.
      /// </summary>
      public bool IsInsideLayer { get; }

      /// <summary>
      /// Computes the conservative stroked bounds of one open polyline.
      /// </summary>
      /// <param name="points">The polyline points.</param>
      /// <param name="pen">The stroke metadata.</param>
      /// <returns>The conservative stroked bounds.</returns>
      public static RectangleF GetConservativeBounds(PointF[] points, Pen pen)
      {
          ArgumentNullException.ThrowIfNull(points);
          if (points.Length == 0)
          {
              return RectangleF.Empty;
          }

          float minX = points[0].X;
          float minY = points[0].Y;
          float maxX = minX;
          float maxY = minY;

          for (int i = 1; i < points.Length; i++)
          {
              PointF point = points[i];
              minX = MathF.Min(minX, point.X);
              minY = MathF.Min(minY, point.Y);
              maxX = MathF.Max(maxX, point.X);
              maxY = MathF.Max(maxY, point.Y);
          }

          RectangleF bounds = RectangleF.FromLTRB(minX, minY, maxX, maxY);
          return InflateBounds(bounds, pen);
      }

      private static RectangleF InflateBounds(RectangleF bounds, Pen pen)
      {
          float halfWidth = pen.StrokeWidth * 0.5F;
          float inflate = pen.StrokeOptions.LineJoin switch
          {
              LineJoin.Miter or LineJoin.MiterRevert or LineJoin.MiterRound => (float)(halfWidth * Math.Max(pen.StrokeOptions.MiterLimit, 1D)),
              _ => halfWidth
          };

          bounds.Inflate(new SizeF(inflate, inflate));
          return bounds;
      }
  }
}