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

namespace SixLabors.Fonts.Rendering {
  /// <summary>
  /// Defines compositing and blending operations used when combining source and destination colors.
  /// <para>
  /// Values 0–12 correspond to standard Porter–Duff compositing modes. These determine how source and
  /// destination alpha interact to produce transparency. The remaining values (13–27) correspond to
  /// separable and non-separable blend modes used in modern graphics systems such as ImageSharp.
  /// </para>
  /// </summary>
  public enum CompositeMode
  {
      // --- Porter–Duff compositing modes ---

      /// <summary>
      /// Clears both the source and destination.
      /// The output is fully transparent regardless of the input colors.
      /// </summary>
      Clear = 0,

      /// <summary>
      /// Replaces the destination entirely with the source.
      /// The destination pixels are ignored.
      /// </summary>
      Src = 1,

      /// <summary>
      /// Keeps the destination as-is and ignores the source.
      /// Equivalent to no drawing operation.
      /// </summary>
      Dest = 2,

      /// <summary>
      /// Draws the source over the destination using standard alpha compositing.
      /// The source appears on top and the destination shows through transparent areas.
      /// </summary>
      SrcOver = 3,

      /// <summary>
      /// Draws the destination over the source.
      /// The destination appears on top and the source shows through transparent areas.
      /// </summary>
      DestOver = 4,

      /// <summary>
      /// Shows the source only where it overlaps the destination.
      /// The destination’s alpha acts as a mask for the source.
      /// </summary>
      SrcIn = 5,

      /// <summary>
      /// Shows the destination only where it overlaps the source.
      /// The source’s alpha acts as a mask for the destination.
      /// </summary>
      DestIn = 6,

      /// <summary>
      /// Shows the source only where it does not overlap the destination.
      /// Produces the inverse of <see cref="SrcIn"/>.
      /// </summary>
      SrcOut = 7,

      /// <summary>
      /// Shows the destination only where it does not overlap the source.
      /// Produces the inverse of <see cref="DestIn"/>.
      /// </summary>
      DestOut = 8,

      /// <summary>
      /// Draws the source over the destination but only within the destination’s alpha region.
      /// Outside that region, the destination remains unchanged.
      /// </summary>
      SrcAtop = 9,

      /// <summary>
      /// Draws the destination over the source but only within the source’s alpha region.
      /// Outside that region, the source is visible.
      /// </summary>
      DestAtop = 10,

      /// <summary>
      /// Exclusive OR.
      /// Shows the source and destination only where they do not overlap.
      /// Overlapping regions become transparent.
      /// </summary>
      Xor = 11,

      /// <summary>
      /// Adds the source and destination color values.
      /// Alpha is also added, producing a brightening effect.
      /// </summary>
      Plus = 12,

      // --- Separable and non-separable blend modes ---

      /// <summary>
      /// Combines colors using an inverse multiply.
      /// Formula: <c>1 − (1 − S) × (1 − D)</c>.
      /// Produces a lighter result similar to photographic screen exposure.
      /// </summary>
      Screen = 13,

      /// <summary>
      /// Multiplies or screens colors depending on destination lightness.
      /// Preserves highlights and shadows while mixing source and destination tones.
      /// </summary>
      Overlay = 14,

      /// <summary>
      /// Chooses the darker of source and destination values per color channel.
      /// </summary>
      Darken = 15,

      /// <summary>
      /// Chooses the lighter of source and destination values per color channel.
      /// </summary>
      Lighten = 16,

      /// <summary>
      /// Brightens the destination to reflect the source.
      /// Formula: <c>D / (1 − S)</c>.
      /// </summary>
      ColorDodge = 17,

      /// <summary>
      /// Darkens the destination to reflect the source.
      /// Formula: <c>1 − (1 − D) / S</c>.
      /// </summary>
      ColorBurn = 18,

      /// <summary>
      /// Applies overlay logic using the source’s lightness.
      /// Used for strong highlight and shadow effects.
      /// </summary>
      HardLight = 19,

      /// <summary>
      /// Similar to <see cref="HardLight"/>, but with reduced contrast.
      /// Produces a softer transition between tones.
      /// </summary>
      SoftLight = 20,

      /// <summary>
      /// Subtracts darker colors from lighter ones to highlight differences.
      /// Often used for comparison or edge detection effects.
      /// </summary>
      Difference = 21,

      /// <summary>
      /// Similar to <see cref="Difference"/>, but with reduced contrast.
      /// Midtones are preserved, producing a lower-contrast difference.
      /// </summary>
      Exclusion = 22,

      /// <summary>
      /// Multiplies source and destination colors.
      /// Always results in a darker composite.
      /// </summary>
      Multiply = 23,

      /// <summary>
      /// Combines the hue of the source with the saturation and luminosity of the destination.
      /// </summary>
      Hue = 24,

      /// <summary>
      /// Combines the saturation of the source with the hue and luminosity of the destination.
      /// </summary>
      Saturation = 25,

      /// <summary>
      /// Combines the hue and saturation of the source with the luminosity of the destination.
      /// </summary>
      Color = 26,

      /// <summary>
      /// Combines the luminosity of the source with the hue and saturation of the destination.
      /// </summary>
      Luminosity = 27
  }
}