103 lines
6.3 KiB
C#
103 lines
6.3 KiB
C#
// Copyright (c) Six Labors.
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// Licensed under the Six Labors Split License.
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using System.IO;
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namespace SixLabors.Fonts.Tables.AdvancedTypographic {
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/// <summary>
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/// A ChainedClassSequenceRule table describes a chained context rule using glyph class values
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/// for backtrack, input, and lookahead sequences.
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/// <see href="https://learn.microsoft.com/en-us/typography/opentype/spec/chapter2#chained-sequence-context-format-2-class-based-glyph-contexts"/>
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/// </summary>
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internal sealed class ChainedClassSequenceRuleTable
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{
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/// <summary>
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/// Initializes a new instance of the <see cref="ChainedClassSequenceRuleTable"/> class.
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/// </summary>
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/// <param name="backtrackSequence">The array of backtrack-sequence classes.</param>
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/// <param name="inputSequence">The array of input sequence classes, beginning with the second glyph position.</param>
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/// <param name="lookaheadSequence">The array of lookahead-sequence classes.</param>
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/// <param name="seqLookupRecords">The array of sequence lookup records.</param>
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private ChainedClassSequenceRuleTable(
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ushort[] backtrackSequence,
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ushort[] inputSequence,
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ushort[] lookaheadSequence,
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SequenceLookupRecord[] seqLookupRecords)
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{
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this.BacktrackSequence = backtrackSequence;
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this.InputSequence = inputSequence;
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this.LookaheadSequence = lookaheadSequence;
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this.SequenceLookupRecords = seqLookupRecords;
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}
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/// <summary>
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/// Gets the array of backtrack-sequence classes.
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/// </summary>
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public ushort[] BacktrackSequence { get; }
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/// <summary>
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/// Gets the array of input sequence classes, beginning with the second glyph position.
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/// </summary>
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public ushort[] InputSequence { get; }
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/// <summary>
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/// Gets the array of lookahead-sequence classes.
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/// </summary>
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public ushort[] LookaheadSequence { get; }
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/// <summary>
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/// Gets the array of sequence lookup records specifying actions to be applied.
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/// </summary>
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public SequenceLookupRecord[] SequenceLookupRecords { get; }
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/// <summary>
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/// Loads the <see cref="ChainedClassSequenceRuleTable"/> from the binary reader at the specified offset.
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/// </summary>
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/// <param name="reader">The big endian binary reader.</param>
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/// <param name="offset">Offset from the beginning of the ChainedClassSequenceRule table.</param>
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/// <returns>The <see cref="ChainedClassSequenceRuleTable"/>.</returns>
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public static ChainedClassSequenceRuleTable Load(BigEndianBinaryReader reader, long offset)
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{
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// ChainedClassSequenceRule
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// +----------------------+----------------------------------------+--------------------------------------------+
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// | Type | Name | Description |
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// +======================+========================================+============================================+
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// | uint16 | backtrackGlyphCount | Number of glyphs in the backtrack |
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// | | | sequence |
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// +----------------------+----------------------------------------+--------------------------------------------+
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// | uint16 | backtrackSequence[backtrackGlyphCount] | Array of backtrack-sequence classes |
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// +----------------------+----------------------------------------+--------------------------------------------+
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// | uint16 | inputGlyphCount | Total number of glyphs in the input |
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// | | | sequence |
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// +----------------------+----------------------------------------+--------------------------------------------+
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// | uint16 | inputSequence[inputGlyphCount - 1] | Array of input sequence classes, beginning |
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// | | | with the second glyph position |
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// +----------------------+----------------------------------------+--------------------------------------------+
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// | uint16 | lookaheadGlyphCount | Number of glyphs in the lookahead |
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// | | | sequence |
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// +----------------------+----------------------------------------+--------------------------------------------+
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// | uint16 | lookaheadSequence[lookaheadGlyphCount] | Array of lookahead-sequence classes |
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// +----------------------+----------------------------------------+--------------------------------------------+
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// | uint16 | seqLookupCount | Number of SequenceLookupRecords |
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// +----------------------+----------------------------------------+--------------------------------------------+
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// | SequenceLookupRecord | seqLookupRecords[seqLookupCount] | Array of SequenceLookupRecords |
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// +----------------------+----------------------------------------+--------------------------------------------+
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reader.Seek(offset, SeekOrigin.Begin);
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ushort backtrackGlyphCount = reader.ReadUInt16();
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ushort[] backtrackSequence = reader.ReadUInt16Array(backtrackGlyphCount);
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ushort inputGlyphCount = reader.ReadUInt16();
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ushort[] inputSequence = reader.ReadUInt16Array(inputGlyphCount - 1);
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ushort lookaheadGlyphCount = reader.ReadUInt16();
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ushort[] lookaheadSequence = reader.ReadUInt16Array(lookaheadGlyphCount);
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ushort seqLookupCount = reader.ReadUInt16();
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SequenceLookupRecord[] seqLookupRecords = SequenceLookupRecord.LoadArray(reader, seqLookupCount);
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return new ChainedClassSequenceRuleTable(backtrackSequence, inputSequence, lookaheadSequence, seqLookupRecords);
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}
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}
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}
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