61 lines
3.2 KiB
C#
61 lines
3.2 KiB
C#
// Copyright (c) Six Labors.
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// Licensed under the Six Labors Split License.
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using System;
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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 SequenceRuleSet table contains an array of SequenceRule tables that define context rules
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/// for simple (glyph ID based) glyph contexts in Sequence Context Format 1.
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/// <see href="https://learn.microsoft.com/en-us/typography/opentype/spec/chapter2#sequence-context-format-1-simple-glyph-contexts"/>
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/// </summary>
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internal sealed class SequenceRuleSetTable
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{
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/// <summary>
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/// Initializes a new instance of the <see cref="SequenceRuleSetTable"/> class.
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/// </summary>
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/// <param name="sequenceRuleTables">The array of sequence rule tables.</param>
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private SequenceRuleSetTable(SequenceRuleTable[] sequenceRuleTables)
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=> this.SequenceRuleTables = sequenceRuleTables;
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/// <summary>
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/// Gets the array of sequence rule tables.
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/// </summary>
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public SequenceRuleTable[] SequenceRuleTables { get; }
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/// <summary>
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/// Loads the <see cref="SequenceRuleSetTable"/> 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 SequenceRuleSet table.</param>
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/// <returns>The <see cref="SequenceRuleSetTable"/>.</returns>
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public static SequenceRuleSetTable Load(BigEndianBinaryReader reader, long offset)
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{
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// SequenceRuleSet
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// +----------+------------------------------+----------------------------------------------------------------+
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// | Type | Name | Description |
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// +==========+==============================+================================================================+
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// | uint16 | seqRuleCount | Number of SequenceRule tables |
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// +----------+------------------------------+----------------------------------------------------------------+
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// | Offset16 | seqRuleOffsets[posRuleCount] | Array of offsets to SequenceRule tables, from beginning of the |
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// | | | SequenceRuleSet table |
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// +----------+------------------------------+----------------------------------------------------------------+
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reader.Seek(offset, SeekOrigin.Begin);
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ushort seqRuleCount = reader.ReadUInt16();
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using Buffer<ushort> seqRuleOffsetsBuffer = new(seqRuleCount);
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Span<ushort> seqRuleOffsets = seqRuleOffsetsBuffer.GetSpan();
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reader.ReadUInt16Array(seqRuleOffsets);
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var sequenceRuleTables = new SequenceRuleTable[seqRuleCount];
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for (int i = 0; i < sequenceRuleTables.Length; i++)
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{
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sequenceRuleTables[i] = SequenceRuleTable.Load(reader, offset + seqRuleOffsets[i]);
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}
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return new SequenceRuleSetTable(sequenceRuleTables);
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}
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}
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}
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