ImageSharp/SixLabors.Fonts/StreamFontMetrics.Cff.cs

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

using System;
using System.Numerics;
using SixLabors.Fonts.Rendering;
using SixLabors.Fonts.Tables.AdvancedTypographic;
using SixLabors.Fonts.Tables.AdvancedTypographic.Variations;
using SixLabors.Fonts.Tables.Cff;
using SixLabors.Fonts.Tables.General;
using SixLabors.Fonts.Tables.General.Colr;
using SixLabors.Fonts.Tables.General.Kern;
using SixLabors.Fonts.Tables.General.Name;
using SixLabors.Fonts.Tables.General.Post;
using SixLabors.Fonts.Tables.General.Svg;
using SixLabors.Fonts.Unicode;

namespace SixLabors.Fonts {
  /// <content>
  /// Contains CFF specific methods.
  /// </content>
  internal partial class StreamFontMetrics
  {
      private static StreamFontMetrics LoadCompactFont(FontReader reader)
      {
          // Load using recommended order for best performance.
          // https://learn.microsoft.com/en-gb/typography/opentype/spec/recom#optimized-table-ordering
          // 'head', 'hhea', 'maxp', OS/2, 'name', 'cmap', 'post', 'CFF ' / 'CFF2'
          HeadTable head = reader.GetTable<HeadTable>();
          HorizontalHeadTable hhea = reader.GetTable<HorizontalHeadTable>();
          MaximumProfileTable maxp = reader.GetTable<MaximumProfileTable>();
          OS2Table os2 = reader.GetTable<OS2Table>();
          NameTable name = reader.GetTable<NameTable>();
          CMapTable cmap = reader.GetTable<CMapTable>();
          PostTable post = reader.GetTable<PostTable>();
          ICffTable? cff =
              (reader.TryGetTable<Cff1Table>() ?? (ICffTable?)reader.TryGetTable<Cff2Table>())
              ?? throw new InvalidFontFileException("Missing required CFF table.");

          // TODO: VORG
          HorizontalMetricsTable htmx = reader.GetTable<HorizontalMetricsTable>();
          VerticalHeadTable? vhea = reader.TryGetTable<VerticalHeadTable>();
          VerticalMetricsTable? vmtx = null;
          if (vhea is not null)
          {
              vmtx = reader.TryGetTable<VerticalMetricsTable>();
          }

          KerningTable? kern = reader.TryGetTable<KerningTable>();

          GlyphDefinitionTable? gdef = reader.TryGetTable<GlyphDefinitionTable>();
          GSubTable? gSub = reader.TryGetTable<GSubTable>();
          GPosTable? gPos = reader.TryGetTable<GPosTable>();

          ColrTable? colr = reader.TryGetTable<ColrTable>();
          CpalTable? cpal = reader.TryGetTable<CpalTable>();
          SvgTable? svg = reader.TryGetTable<SvgTable>();

          // Variations related tables.
          FVarTable? fVar = reader.TryGetTable<FVarTable>();
          AVarTable? aVar = reader.TryGetTable<AVarTable>();
          GVarTable? gVar = reader.TryGetTable<GVarTable>();
          HVarTable? hVar = reader.TryGetTable<HVarTable>();
          VVarTable? vVar = reader.TryGetTable<VVarTable>();
          MVarTable? mVar = reader.TryGetTable<MVarTable>();

          GlyphVariationProcessor? glyphVariationProcessor = null;
          if (cff.ItemVariationStore != null)
          {
              if (fVar is null)
              {
                  throw new InvalidFontFileException("missing fvar table required for glyph variations processing");
              }

              glyphVariationProcessor = new GlyphVariationProcessor(cff.ItemVariationStore, fVar, aVar, gVar, hVar, vVar, mVar);
          }

          CompactFontTables tables = new(cmap, head, hhea, htmx, maxp, name, os2, post, cff)
          {
              Kern = kern,
              Vhea = vhea,
              Vmtx = vmtx,
              Gdef = gdef,
              GSub = gSub,
              GPos = gPos,
              Colr = colr,
              Cpal = cpal,
              FVar = fVar,
              AVar = aVar,
              GVar = gVar,
              HVar = hVar,
              VVar = vVar,
              MVar = mVar,
              Svg = svg
          };

          return new StreamFontMetrics(tables, glyphVariationProcessor);
      }

      private FontGlyphMetrics CreateCffGlyphMetrics(
          in CodePoint codePoint,
          ushort glyphId,
          GlyphType glyphType,
          TextAttributes textAttributes,
          TextDecorations textDecorations,
          ColorFontSupport colorSupport,
          bool isVerticalLayout,
          ushort paletteIndex = 0)
      {
          // TODO: When do we require and how do we use the palette index?
          CompactFontTables tables = this.compactFontTables!;
          ICffTable cff = tables.Cff;
          HorizontalMetricsTable htmx = tables.Htmx;
          VerticalMetricsTable? vtmx = tables.Vmtx;
          FVarTable? fVar = tables.FVar;
          AVarTable? aVar = tables.AVar;
          GVarTable? gVar = tables.GVar;

          CffGlyphData vector = cff.GetGlyph(glyphId);
          vector.FVar = fVar;
          vector.AVar = aVar;
          vector.GVar = gVar;
          Bounds bounds = vector.GetBounds();

          // Apply the CFF FontMatrix to transform bounds from charstring space to design units.
          if (vector.FontMatrix is double[] fm)
          {
              float upm = this.UnitsPerEm;
              Vector2 fmScale = new((float)(fm[0] * upm), (float)(fm[3] * upm));
              bounds = new Bounds(bounds.Min * fmScale, bounds.Max * fmScale);
          }

          ushort advanceWidth = htmx.GetAdvancedWidth(glyphId);
          short lsb = htmx.GetLeftSideBearing(glyphId);

          // Apply HVAR advance width adjustment if available.
          if (this.GlyphVariationProcessor is not null)
          {
              advanceWidth = (ushort)(advanceWidth + MathF.Round(this.GlyphVariationProcessor.AdvanceAdjustment(glyphId)));
          }

          IMetricsHeader metrics = isVerticalLayout ? this.VerticalMetrics : this.HorizontalMetrics;
          ushort advancedHeight = (ushort)(metrics.Ascender - metrics.Descender);
          short tsb = (short)(metrics.Ascender - bounds.Max.Y);
          if (vtmx != null)
          {
              advancedHeight = vtmx.GetAdvancedHeight(glyphId);
              tsb = vtmx.GetTopSideBearing(glyphId);
          }

          // Apply VVAR advance height adjustment if available.
          if (this.GlyphVariationProcessor is not null)
          {
              advancedHeight = (ushort)(advancedHeight + MathF.Round(this.GlyphVariationProcessor.VerticalAdvanceAdjustment(glyphId)));
          }

          // TODO: Support CFF based COLR glyphs.
          // This requires parsing the CFF charstrings to extract the glyph vectors.
          SvgTable? svg = tables.Svg;
          if ((colorSupport & ColorFontSupport.Svg) == ColorFontSupport.Svg && svg?.ContainsGlyph(glyphId) == true)
          {
              return new PaintedGlyphMetrics(
                  this,
                  glyphId,
                  codePoint,
                  this.GetOrCreateSvgGlyphSource(svg),
                  bounds,
                  advanceWidth,
                  advancedHeight,
                  lsb,
                  tsb,
                  this.UnitsPerEm,
                  textAttributes,
                  textDecorations);
          }

          return new CffGlyphMetrics(
              this,
              glyphId,
              codePoint,
              vector,
              bounds,
              advanceWidth,
              advancedHeight,
              lsb,
              tsb,
              this.UnitsPerEm,
              textAttributes,
              textDecorations,
              glyphType);
      }
  }
}