ImageSharp/ImageSharp.Drawing/Processing/RecolorBrush.cs

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

using System;
using System.Numerics;
using SixLabors.ImageSharp.Memory;
using SixLabors.ImageSharp.PixelFormats;

namespace SixLabors.ImageSharp.Drawing.Processing {
  /// <summary>
  /// Provides an implementation of a brush that can recolor an image
  /// </summary>
  public sealed class RecolorBrush : Brush
  {
      /// <summary>
      /// Initializes a new instance of the <see cref="RecolorBrush" /> class.
      /// </summary>
      /// <param name="sourceColor">Color of the source.</param>
      /// <param name="targetColor">Color of the target.</param>
      /// <param name="threshold">The threshold as a value between 0 and 1.</param>
      public RecolorBrush(Color sourceColor, Color targetColor, float threshold)
      {
          this.SourceColor = sourceColor;
          this.Threshold = threshold;
          this.TargetColor = targetColor;
      }

      /// <summary>
      /// Gets the threshold.
      /// </summary>
      public float Threshold { get; }

      /// <summary>
      /// Gets the source color.
      /// </summary>
      public Color SourceColor { get; }

      /// <summary>
      /// Gets the target color.
      /// </summary>
      public Color TargetColor { get; }

      /// <inheritdoc />
      public override BrushRenderer<TPixel> CreateRenderer<TPixel>(
          Configuration configuration,
          GraphicsOptions options,
          int canvasWidth,
          RectangleF region)
          => new RecolorBrushRenderer<TPixel>(
              configuration,
              options,
              canvasWidth,
              this.SourceColor.ToPixel<TPixel>(),
              this.TargetColor.ToPixel<TPixel>(),
              this.Threshold);

      /// <inheritdoc />
      public override bool Equals(Brush? other)
      {
          if (other is RecolorBrush brush)
          {
              return this.SourceColor.Equals(brush.SourceColor)
                  && this.TargetColor.Equals(brush.TargetColor)
                  && this.Threshold == brush.Threshold;
          }

          return false;
      }

      /// <inheritdoc/>
      public override int GetHashCode()
          => HashCode.Combine(this.Threshold, this.SourceColor, this.TargetColor);

      /// <summary>
      /// The recolor brush applicator.
      /// </summary>
      /// <typeparam name="TPixel">The pixel format.</typeparam>
      private sealed class RecolorBrushRenderer<TPixel> : BrushRenderer<TPixel>
          where TPixel : unmanaged, IPixel<TPixel>
      {
          private readonly Vector4 sourceColor;
          private readonly float threshold;
          private readonly TPixel targetColorPixel;

          /// <summary>
          /// Initializes a new instance of the <see cref="RecolorBrushRenderer{TPixel}" /> class.
          /// </summary>
          /// <param name="configuration">The configuration instance to use when performing operations.</param>
          /// <param name="options">The options</param>
          /// <param name="canvasWidth">The canvas width for the current render pass.</param>
          /// <param name="sourceColor">Color of the source.</param>
          /// <param name="targetColor">Color of the target.</param>
          /// <param name="threshold">The threshold .</param>
          public RecolorBrushRenderer(
              Configuration configuration,
              GraphicsOptions options,
              int canvasWidth,
              TPixel sourceColor,
              TPixel targetColor,
              float threshold)
              : base(configuration, options, canvasWidth)
          {
              this.sourceColor = sourceColor.ToScaledVector4();
              this.targetColorPixel = targetColor;

              // TODO: Review this. We can skip the conversion from/to Vector4.
              // Lets hack a min max extremes for a color space by letting the IPackedPixel clamp our values to something in the correct spaces :)
              TPixel maxColor = TPixel.FromVector4(new Vector4(float.MaxValue));
              TPixel minColor = TPixel.FromVector4(new Vector4(float.MinValue));
              this.threshold = Vector4.DistanceSquared(maxColor.ToVector4(), minColor.ToVector4()) * threshold;
          }

          /// <inheritdoc />
          public override void Apply(
              Span<TPixel> destinationRow,
              ReadOnlySpan<float> scanline,
              int x,
              int y,
              BrushWorkspace<TPixel> workspace)
          {
              Span<float> amounts = workspace.GetAmounts(scanline.Length);
              Span<TPixel> overlays = workspace.GetOverlays(scanline.Length);

              for (int i = 0; i < scanline.Length; i++)
              {
                  amounts[i] = scanline[i] * this.Options.BlendPercentage;
                  TPixel result = destinationRow[i];
                  Vector4 background = result.ToVector4();
                  float distance = Vector4.DistanceSquared(background, this.sourceColor);
                  overlays[i] = distance <= this.threshold
                      ? this.Blender.Blend(result, this.targetColorPixel, (this.threshold - distance) / this.threshold)
                      : result;
              }

              this.Blender.Blend(
                  this.Configuration,
                  destinationRow,
                  destinationRow,
                  overlays,
                  amounts,
                  workspace.GetBlendScratch(scanline.Length, 3));
          }
      }
  }
}