ImageSharp/SixLabors.Fonts/Rendering/Paint.cs

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

using System.Numerics;

namespace SixLabors.Fonts.Rendering {
  /// <summary>
  /// Base type for normalized paint definitions that can be used by any renderer.
  /// Glyph sources must pre-apply all relevant transforms and resolve any palette
  /// or format-specific constructs before creating a paint instance.
  /// </summary>
  public abstract class Paint
  {
      /// <summary>
      /// Gets the per-layer opacity multiplier in the range [0, 1].
      /// Renderers should multiply this value into the alpha channel of the final brush.
      /// </summary>
      public float Opacity { get; init; } = 1f;

      /// <summary>
      /// Gets or sets an optional transform to apply to the paint.
      /// Used to pre-apply gradientTransform in SVG or equivalent.
      /// </summary>
      internal Matrix3x2 Transform { get; set; }

      /// <summary>
      /// Gets the composite mode to use when applying this paint over existing content.
      /// </summary>
      public CompositeMode CompositeMode { get; init; } = CompositeMode.SrcOver;
  }

  /// <summary>
  /// Solid color paint (direct RGBA). Interpreters must resolve palettes to RGBA.
  /// Compatible with OT-SVG solid fills and COLR v1 PaintSolid after CPAL resolution.
  /// </summary>
  public sealed class SolidPaint : Paint
  {
      /// <summary>
      /// Gets the color to use for the fill. Alpha is respected and further multiplied by <see cref="Paint.Opacity"/>.
      /// </summary>
      public GlyphColor Color { get; init; }
  }

  /// <summary>
  /// Linear gradient paint.
  /// </summary>
  public sealed class LinearGradientPaint : Paint
  {
      /// <summary>
      /// Gets the coordinate system for <see cref="P0"/> and <see cref="P1"/>.
      /// </summary>
      internal GradientUnits Units { get; init; }

      /// <summary>
      /// Gets the gradient start point. Normalized if <see cref="Units"/> is <see cref="GradientUnits.ObjectBoundingBox"/>.
      /// </summary>
      public Vector2 P0 { get; init; }

      /// <summary>
      /// Gets the gradient end point. Normalized if <see cref="Units"/> is <see cref="GradientUnits.ObjectBoundingBox"/>.
      /// </summary>
      public Vector2 P1 { get; init; }

      /// <summary>
      /// Gets the rotation point for the gradient. Normalized if <see cref="Units"/> is <see cref="GradientUnits.ObjectBoundingBox"/>.
      /// </summary>
      public Vector2? P2 { get; init; }

      /// <summary>
      /// Gets the spread method applied when sampling outside the [0, 1] range.
      /// </summary>
      public SpreadMethod Spread { get; init; } = SpreadMethod.Pad;

      /// <summary>
      /// Gets the ordered gradient stops (ascending by <see cref="GradientStop.Offset"/>).
      /// </summary>
      public GradientStop[] Stops { get; init; } = [];
  }

  /// <summary>
  /// Represents a radial gradient paint defined by two circles.
  /// The first circle is centered at <see cref="Center0"/> with radius <see cref="Radius0"/>.
  /// The second circle is centered at <see cref="Center1"/> with radius <see cref="Radius1"/>.
  /// The color transition is computed between these two circles.
  /// Compatible with two-circle radial gradients used by HTML Canvas and OpenType COLR v1.
  /// </summary>
  public sealed class RadialGradientPaint : Paint
  {
      /// <summary>
      /// Gets the coordinate system for <see cref="Center0"/>, <see cref="Center1"/>,
      /// <see cref="Radius0"/>, and <see cref="Radius1"/>.
      /// </summary>
      internal GradientUnits Units { get; init; }

      /// <summary>
      /// Gets the center of the starting circle of the gradient.
      /// </summary>
      public Vector2 Center0 { get; init; }

      /// <summary>
      /// Gets the radius of the starting circle of the gradient.
      /// If <see cref="Units"/> is <see cref="GradientUnits.ObjectBoundingBox"/>,
      /// the radius is normalized to the bounds.
      /// </summary>
      public float Radius0 { get; init; }

      /// <summary>
      /// Gets the center of the ending circle of the gradient.
      /// </summary>
      public Vector2 Center1 { get; init; }

      /// <summary>
      /// Gets the radius of the ending circle of the gradient.
      /// If <see cref="Units"/> is <see cref="GradientUnits.ObjectBoundingBox"/>,
      /// the radius is normalized to the bounds.
      /// </summary>
      public float Radius1 { get; init; }

      /// <summary>
      /// Gets the spread method applied when sampling outside the [0, 1] range.
      /// </summary>
      public SpreadMethod Spread { get; init; } = SpreadMethod.Pad;

      /// <summary>
      /// Gets the ordered gradient stops, ascending by <see cref="GradientStop.Offset"/>.
      /// </summary>
      public GradientStop[] Stops { get; init; } = [];
  }

  /// <summary>
  /// Sweep (conic) gradient paint. Angles are expressed in degrees in the renderer's y-down space.
  /// </summary>
  public sealed class SweepGradientPaint : Paint
  {
      /// <summary>
      /// Gets the coordinate system for <see cref="Center"/>. Sweep gradients are typically user-space.
      /// </summary>
      internal GradientUnits Units { get; init; } = GradientUnits.UserSpaceOnUse;

      /// <summary>
      /// Gets the center of the sweep gradient.
      /// </summary>
      public Vector2 Center { get; init; }

      /// <summary>
      /// Gets the start angle in degrees.
      /// </summary>
      public float StartAngle { get; init; }

      /// <summary>
      /// Gets the end angle in degrees.
      /// </summary>
      public float EndAngle { get; init; }

      /// <summary>
      /// Gets the spread method applied when sampling outside the [0, 1] range.
      /// </summary>
      public SpreadMethod Spread { get; init; } = SpreadMethod.Pad;

      /// <summary>
      /// Gets the ordered gradient stops (ascending by <see cref="GradientStop.Offset"/>).
      /// </summary>
      public GradientStop[] Stops { get; init; } = [];
  }
}