ImageSharp/ImageSharp.Drawing/Processing/Backends/DefaultRasterizer.RasterizableGeometry.cs

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

using System;
using System.Buffers;

namespace SixLabors.ImageSharp.Drawing.Processing.Backends {
  internal static partial class DefaultRasterizer
  {
      /// <summary>
      /// Flush-scoped retained row-local raster payload for one prepared fill geometry.
      /// </summary>
      internal sealed class RasterizableGeometry : IDisposable
      {
          private readonly RasterizableBandInfo[] bandInfos;
          private readonly LineArrayX16Y16Block?[]? linesX16;
          private readonly LineArrayX32Y16Block?[]? linesX32;
          private readonly int[] firstBlockLineCounts;
          private readonly IMemoryOwner<int>?[] startCoverTable;

          /// <summary>
          /// Initializes a new instance of the <see cref="RasterizableGeometry"/> class.
          /// </summary>
          /// <param name="firstRowBandIndex">The first absolute row-band index touched by the geometry.</param>
          /// <param name="rowBandCount">The number of retained local row bands owned by the geometry.</param>
          /// <param name="width">The geometry-local visible band width in pixels.</param>
          /// <param name="wordsPerRow">The bit-vector width in machine words required by the geometry.</param>
          /// <param name="coverStride">The scanner cover/area stride required by the geometry.</param>
          /// <param name="bandHeight">The retained row-band height in pixels.</param>
          /// <param name="isX16">Indicates whether the geometry uses the narrow X16Y16 line encoding.</param>
          /// <param name="bandInfos">The retained metadata for each local row band.</param>
          /// <param name="linesX16">The retained narrow line chains for each local row band.</param>
          /// <param name="linesX32">The retained wide line chains for each local row band.</param>
          /// <param name="firstBlockLineCounts">The valid line count in each front retained block.</param>
          /// <param name="startCoverTable">The retained start-cover table for each local row band.</param>
          public RasterizableGeometry(
              int firstRowBandIndex,
              int rowBandCount,
              int width,
              int wordsPerRow,
              int coverStride,
              int bandHeight,
              bool isX16,
              RasterizableBandInfo[] bandInfos,
              LineArrayX16Y16Block?[]? linesX16,
              LineArrayX32Y16Block?[]? linesX32,
              int[] firstBlockLineCounts,
              IMemoryOwner<int>?[] startCoverTable)
          {
              this.FirstRowBandIndex = firstRowBandIndex;
              this.RowBandCount = rowBandCount;
              this.Width = width;
              this.WordsPerRow = wordsPerRow;
              this.CoverStride = coverStride;
              this.BandHeight = bandHeight;
              this.IsX16 = isX16;
              this.bandInfos = bandInfos;
              this.linesX16 = linesX16;
              this.linesX32 = linesX32;
              this.firstBlockLineCounts = firstBlockLineCounts;
              this.startCoverTable = startCoverTable;
          }

          /// <summary>
          /// Gets the first absolute row-band index touched by this geometry.
          /// </summary>
          public int FirstRowBandIndex { get; }

          /// <summary>
          /// Gets the number of retained local row bands owned by this geometry.
          /// </summary>
          public int RowBandCount { get; }

          /// <summary>
          /// Gets the geometry-local visible band width in pixels.
          /// </summary>
          public int Width { get; }

          /// <summary>
          /// Gets the bit-vector width in machine words required by this geometry.
          /// </summary>
          public int WordsPerRow { get; }

          /// <summary>
          /// Gets the scanner cover/area stride required by this geometry.
          /// </summary>
          public int CoverStride { get; }

          /// <summary>
          /// Gets the retained row-band height in pixels.
          /// </summary>
          public int BandHeight { get; }

          /// <summary>
          /// Gets a value indicating whether this geometry uses Blaze's narrow X16Y16 line arrays.
          /// </summary>
          public bool IsX16 { get; }

          /// <summary>
          /// Returns <see langword="true"/> when the given local row band has retained coverage payload.
          /// </summary>
          /// <param name="localRowIndex">The local row band index.</param>
          /// <returns><see langword="true"/> when the row band has retained coverage; otherwise <see langword="false"/>.</returns>
          public bool HasCoverage(int localRowIndex) => this.bandInfos[localRowIndex].HasCoverage;

          /// <summary>
          /// Gets the retained narrow line block chain for one local row.
          /// </summary>
          /// <param name="localRowIndex">The local row band index.</param>
          /// <returns>The retained narrow line chain for the row.</returns>
          public LineArrayX16Y16Block? GetLinesX16ForRow(int localRowIndex) => this.linesX16![localRowIndex];

          /// <summary>
          /// Gets the retained wide line block chain for one local row.
          /// </summary>
          /// <param name="localRowIndex">The local row band index.</param>
          /// <returns>The retained wide line chain for the row.</returns>
          public LineArrayX32Y16Block? GetLinesX32ForRow(int localRowIndex) => this.linesX32![localRowIndex];

          /// <summary>
          /// Gets the number of valid lines in the first retained block for a local row.
          /// </summary>
          /// <param name="localRowIndex">The local row band index.</param>
          /// <returns>The valid line count in the front retained block.</returns>
          public int GetFirstBlockLineCountForRow(int localRowIndex) => this.firstBlockLineCounts[localRowIndex];

          /// <summary>
          /// Gets the retained start-cover table entry for a local row, if one exists.
          /// </summary>
          /// <param name="localRowIndex">The local row band index.</param>
          /// <returns>The retained start-cover span for the row.</returns>
          public ReadOnlySpan<int> GetCoversForRow(int localRowIndex)
          {
              IMemoryOwner<int>? covers = this.startCoverTable[localRowIndex];
              return covers is null ? ReadOnlySpan<int>.Empty : covers.Memory.Span[..this.BandHeight];
          }

          /// <summary>
          /// Gets the retained start-cover row payload without further interpretation, matching Blaze naming.
          /// </summary>
          /// <param name="localRowIndex">The local row band index.</param>
          /// <returns>The retained start-cover span for the row.</returns>
          public ReadOnlySpan<int> GetActualCoversForRow(int localRowIndex) => this.GetCoversForRow(localRowIndex);

          /// <summary>
          /// Gets retained metadata for one local row band.
          /// </summary>
          /// <param name="localRowIndex">The local row band index.</param>
          /// <returns>The retained band metadata.</returns>
          public RasterizableBandInfo GetBandInfo(int localRowIndex) => this.bandInfos[localRowIndex];

          /// <summary>
          /// Releases the retained line blocks and start-cover storage.
          /// </summary>
          public void Dispose()
          {
              if (this.linesX16 is not null)
              {
                  Array.Clear(this.linesX16);
              }

              if (this.linesX32 is not null)
              {
                  Array.Clear(this.linesX32);
              }

              for (int i = 0; i < this.startCoverTable.Length; i++)
              {
                  this.startCoverTable[i]?.Dispose();
              }
          }
      }
  }
}