ImageSharp/SixLabors.Fonts/Tables/Cff/CffBoundsFinder.cs

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

using System;
using System.Numerics;
using SixLabors.Fonts.Rendering;

namespace SixLabors.Fonts.Tables.Cff {
  /// <summary>
  /// Calculates the bounding box of a CFF glyph by implementing <see cref="IGlyphRenderer"/>
  /// and tracking the minimum and maximum coordinates of all path operations.
  /// </summary>
  internal class CffBoundsFinder : IGlyphRenderer
  {
      private float minX;
      private float maxX;
      private float minY;
      private float maxY;
      private Vector2 currentXY;
      private readonly int nsteps;
      private bool open;
      private bool firstEval;

      /// <summary>
      /// Initializes a new instance of the <see cref="CffBoundsFinder"/> class.
      /// </summary>
      public CffBoundsFinder()
      {
          this.minX = float.MaxValue;
          this.maxX = float.MinValue;
          this.minY = float.MaxValue;
          this.maxY = float.MinValue;
          this.nsteps = 3;
          this.currentXY = Vector2.Zero;
          this.open = false;
          this.firstEval = true;
      }

      /// <inheritdoc/>
      public void BeginFigure()
      {
          // Do nothing.
      }

      /// <inheritdoc/>
      public bool BeginGlyph(in FontRectangle bounds, in GlyphRendererParameters parameters)
          => true; // Do nothing.

      /// <inheritdoc/>
      public void BeginText(in FontRectangle bounds)
      {
          // Do nothing.
      }

      /// <inheritdoc/>
      public void EndFigure()
      {
          this.open = false;
          this.currentXY = Vector2.Zero;
      }

      /// <inheritdoc/>
      public void EndGlyph()
      {
          if (this.open)
          {
              this.EndFigure();
          }
      }

      /// <inheritdoc/>
      public void EndText()
      {
          if (this.open)
          {
              this.EndFigure();
          }
      }

      /// <inheritdoc/>
      public void BeginLayer(Paint? paint, FillRule fillRule, ClipQuad? clipBounds)
      {
          // Do nothing.
      }

      /// <inheritdoc/>
      public void EndLayer()
      {
          // Do nothing.
      }

      /// <inheritdoc/>
      public void LineTo(Vector2 point)
      {
          this.currentXY = point;
          this.UpdateMinMax(point.X, point.Y);
          this.open = true;
      }

      /// <inheritdoc/>
      public void MoveTo(Vector2 point)
      {
          if (this.open)
          {
              this.EndFigure();
          }

          this.currentXY = point;
          this.UpdateMinMax(point.X, point.Y);
      }

      /// <inheritdoc/>
      public void ArcTo(float radiusX, float radiusY, float xAxisRotation, bool largeArc, bool sweep, Vector2 point)
      {
          // TODO: check this. I feel like we should have to implement it.
          this.currentXY = point;
          this.UpdateMinMax(point.X, point.Y);
          this.open = true;
      }

      /// <inheritdoc/>
      public void CubicBezierTo(Vector2 secondControlPoint, Vector2 thirdControlPoint, Vector2 point)
      {
          float eachstep = 1F / this.nsteps;
          float t = eachstep; // Start

          for (int n = 1; n < this.nsteps; ++n)
          {
              float c = 1F - t;
              Vector2 xy = (this.currentXY * c * c * c) + (secondControlPoint * 3 * t * c * c) + (thirdControlPoint * 3 * t * t * c) + (point * t * t * t);
              this.UpdateMinMax(xy.X, xy.Y);

              t += eachstep;
          }

          this.currentXY = point;
          this.UpdateMinMax(point.X, point.Y);
          this.open = true;
      }

      /// <inheritdoc/>
      public void QuadraticBezierTo(Vector2 secondControlPoint, Vector2 point)
      {
          float eachstep = 1F / this.nsteps;
          float t = eachstep; // Start

          for (int n = 1; n < this.nsteps; ++n)
          {
              float c = 1F - t;
              Vector2 xy = (this.currentXY * c * c) + (secondControlPoint * 2 * t * c) + (point * t * t);
              this.UpdateMinMax(xy.X, xy.Y);

              t += eachstep;
          }

          this.currentXY = point;
          this.UpdateMinMax(point.X, point.Y);
          this.open = true;
      }

      /// <inheritdoc/>
      public TextDecorations EnabledDecorations()
          => TextDecorations.None;

      /// <inheritdoc/>
      public void SetDecoration(TextDecorations textDecorations, Vector2 start, Vector2 end, float thickness)
      {
          // Do nothing.
      }

      /// <summary>
      /// Updates the tracked minimum and maximum coordinates with the given point.
      /// </summary>
      /// <param name="x0">The x-coordinate to evaluate.</param>
      /// <param name="y0">The y-coordinate to evaluate.</param>
      private void UpdateMinMax(float x0, float y0)
      {
          if (this.firstEval)
          {
              // 4 times
              if (x0 < this.minX)
              {
                  this.minX = x0;
              }

              if (x0 > this.maxX)
              {
                  this.maxX = x0;
              }

              if (y0 < this.minY)
              {
                  this.minY = y0;
              }

              if (y0 > this.maxY)
              {
                  this.maxY = y0;
              }

              this.firstEval = false;
          }
          else
          {
              // 2 times
              if (x0 < this.minX)
              {
                  this.minX = x0;
              }
              else if (x0 > this.maxX)
              {
                  this.maxX = x0;
              }

              if (y0 < this.minY)
              {
                  this.minY = y0;
              }
              else if (y0 > this.maxY)
              {
                  this.maxY = y0;
              }
          }
      }

      /// <summary>
      /// Gets the computed bounding box from all tracked path coordinates.
      /// </summary>
      /// <returns>The <see cref="Bounds"/> representing the glyph bounding box.</returns>
      public Bounds GetBounds()
          => new(
              (short)Math.Floor(this.minX),
              (short)Math.Floor(this.minY),
              (short)Math.Ceiling(this.maxX),
              (short)Math.Ceiling(this.maxY));
  }
}