172 lines
4.1 KiB
C#
172 lines
4.1 KiB
C#
using System;
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using System.Collections.Generic;
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using System.IO;
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using System.Text;
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namespace FontPreview
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{
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/// <summary>
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/// 轻量 cmap 表解析器：纯字节读取字体文件，判断某 Unicode 码点是否有字形。
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/// 支持 TTF/OTF/TTC，覆盖 cmap 格式 4（BMP）与格式 12（全平面）。
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/// 不依赖 GDI+/DirectWrite，跨平台可编译。
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/// </summary>
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public class FontCmap
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{
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private List<int[]> ranges = new List<int[]>(); // 排序的 [start, end] 闭区间
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public static FontCmap Load(string path)
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{
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try
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{
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byte[] d = File.ReadAllBytes(path);
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FontCmap c = new FontCmap();
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c.Parse(d);
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return c.ranges.Count > 0 ? c : null;
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}
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catch
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{
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return null;
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}
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}
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private static ushort RU16(byte[] d, uint o)
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{
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return (ushort)(d[o] * 256u + d[o + 1]);
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}
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private static uint RU32(byte[] d, uint o)
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{
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return (uint)(d[o] * 16777216u + d[o + 1] * 65536u + d[o + 2] * 256u + d[o + 3]);
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}
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private static string Tag(byte[] d, uint o)
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{
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try
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{
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return Encoding.ASCII.GetString(d, (int)o, 4);
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}
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catch { return ""; }
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}
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private void Parse(byte[] d)
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{
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uint sfntOff = 0;
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if (Tag(d, 0) == "ttcf")
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{
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sfntOff = RU32(d, 8); // TTC：第一个字体的偏移
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}
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uint numTables = RU16(d, sfntOff + 4);
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uint cmapOff = 0;
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for (uint i = 0; i < numTables; i++)
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{
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uint rec = sfntOff + 12 + i * 16;
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if (Tag(d, rec) == "cmap")
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{
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cmapOff = RU32(d, rec + 8);
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break;
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}
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}
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if (cmapOff == 0) return;
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uint numSub = RU16(d, cmapOff + 2);
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uint best = 0;
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bool gotFull = false;
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for (uint i = 0; i < numSub; i++)
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{
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uint rec = cmapOff + 4 + i * 8;
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ushort platform = RU16(d, rec);
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ushort enc = RU16(d, rec + 2);
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uint off = cmapOff + RU32(d, rec + 4);
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// Windows: platformID=3；enc=10 为全 Unicode 平面，enc=1 为 BMP
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if (platform == 3 && (enc == 10 || enc == 1))
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{
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if (enc == 10 && !gotFull) { best = off; gotFull = true; }
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else if (best == 0) { best = off; }
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}
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}
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if (best == 0)
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{
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// 退而求其次：任意子表
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if (numSub > 0) best = cmapOff + RU32(d, cmapOff + 8);
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}
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if (best == 0) return;
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ushort fmt = RU16(d, best);
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if (fmt == 4) ParseFormat4(d, best);
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else if (fmt == 12) ParseFormat12(d, best);
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else if (fmt == 0) ParseFormat0(d, best);
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ranges.Sort((a, b) => a[0].CompareTo(b[0]));
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Merge();
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}
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private void ParseFormat4(byte[] d, uint o)
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{
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int segCount = RU16(d, o + 6) / 2;
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uint endOff = o + 14;
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uint startOff = endOff + (uint)segCount * 2 + 2; // 跳过 endCode 与 reservedPad
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for (int i = 0; i < segCount; i++)
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{
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int s = RU16(d, startOff + (uint)i * 2);
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int e = RU16(d, endOff + (uint)i * 2);
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if (s != 0xFFFF && e >= s && s != 0)
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{
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ranges.Add(new int[] { s, e });
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}
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}
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}
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private void ParseFormat12(byte[] d, uint o)
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{
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uint numGroups = RU32(d, o + 12);
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uint g = o + 16;
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for (uint i = 0; i < numGroups; i++)
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{
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int s = (int)RU32(d, g + i * 12);
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int e = (int)RU32(d, g + i * 12 + 4);
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if (e >= s) ranges.Add(new int[] { s, e });
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}
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}
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private void ParseFormat0(byte[] d, uint o)
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{
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// 256 字节 glyph index 表，非 0 即有字形
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int start = -1;
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for (int i = 0; i < 256; i++)
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{
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bool has = d[o + 6 + i] != 0;
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if (has && start < 0) start = i;
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if (!has && start >= 0) { ranges.Add(new int[] { start, i - 1 }); start = -1; }
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}
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if (start >= 0) ranges.Add(new int[] { start, 255 });
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}
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private void Merge()
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{
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List<int[]> merged = new List<int[]>();
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foreach (int[] r in ranges)
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{
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if (merged.Count > 0 && r[0] <= merged[merged.Count - 1][1] + 1)
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{
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if (r[1] > merged[merged.Count - 1][1]) merged[merged.Count - 1][1] = r[1];
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}
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else merged.Add(new int[] { r[0], r[1] });
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}
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ranges = merged;
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}
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public bool HasGlyph(int codepoint)
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{
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int lo = 0, hi = ranges.Count - 1;
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while (lo <= hi)
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{
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int mid = (lo + hi) / 2;
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if (codepoint < ranges[mid][0]) hi = mid - 1;
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else if (codepoint > ranges[mid][1]) lo = mid + 1;
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else return true;
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}
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return false;
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}
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}
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}
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