True Type Font 原理解析

[RedCrazyGhost]

前言

想快速了解TrueTypeFont的同学，请点击查看Apple 字体表

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介绍

TrueTypeFont是由美国苹果公司和微软公司共同开发的一种字体标准。文件扩展名为.ttf

原理

mac/linux 系统可以使用hexdump -C命令查看ttf的二进制

hexdump -C *.ttf

00000000  00 01 00 00 00 10 01 00  00 04 00 00 47 50 4f 53  |............GPOS|
          |----1----| |-2-| |-3-|  |-4-| |-5-| |----6----|
00000010  44 76 4c 75 00 00 04 58  00 00 00 20 47 53 55 42  |DvLu...X... GSUB|
          |----7----| |----8----|  |----9----| |---10----|
00000020  3c 7e 2b 10 00 00 04 78  00 00 00 f0 4f 53 2f 32  |<~+....x....OS/2|
00000030  70 20 5e f1 00 00 02 3c  00 00 00 60 63 6d 61 70  |p ^....<...`cmap|
00000040  00 0c 00 84 00 00 02 9c  00 00 00 34 67 61 73 70  |...........4gasp|
00000050  00 00 00 0b 00 00 04 50  00 00 00 08 67 6c 79 66  |.......P....glyf|
00000060  89 10 b6 c1 00 00 01 0c  00 00 00 a0 68 65 61 64  |............head|
00000070  1b ce e9 70 00 00 01 d4  00 00 00 36 68 68 65 61  |...p.......6hhea|
00000080  08 8b 02 ba 00 00 02 18  00 00 00 24 68 6d 74 78  |...........$hmtx|
00000090  0a 26 01 ce 00 00 02 0c  00 00 00 0c 6c 6f 63 61  |.&..........loca|
000000a0  00 28 00 50 00 00 01 cc  00 00 00 08 6d 61 78 70  |.(.P........maxp|
000000b0  01 92 02 0b 00 00 01 ac  00 00 00 20 6e 61 6d 65  |........... name|
000000c0  19 74 33 e9 00 00 02 d8  00 00 01 58 70 6f 73 74  |.t3........Xpost|
000000d0  ff b8 00 32 00 00 04 30  00 00 00 20 70 72 65 70  |...2...0... prep|
000000e0  70 02 04 12 00 00 02 d0  00 00 00 08 76 68 65 61  |p...........vhea|
000000f0  04 64 00 d9 00 00 05 70  00 00 00 24 76 6d 74 78  |.d.....p...$vmtx|
00000100  04 7d 00 bf 00 00 05 68  00 00 00 08 00 01 00 5c  |.}.....h.......\|
00000110  ff af 01 9f 02 8b 00 18  00 00 13 26 35 34 3f 01  |...........&54?.|
00000120  3e 01 33 32 16 15 11 14  06 23 22 26 35 11 07 06  |>.32.....#"&5...|
00000130  23 22 26 68 0c 10 82 1e  30 17 26 26 2c 1b 1b 2a  |#"&h....0.&&,..*|
00000140  6b 06 06 0e 1d 01 da 1a  14 17 08 42 10 12 2f 27  |k..........B../'|
00000150  fd a6 14 18 18 14 02 12  39 03 17 00 00 01 00 78  |........9......x|
00000160  01 b3 03 53 02 f7 00 18  00 00 01 36 33 32 1f 01  |...S.......632..|
00000170  1e 01 15 14 06 23 21 22  26 35 34 36 33 21 27 26  |.....#!"&5463!'&|
00000180  35 34 36 02 a2 18 15 18  08 42 10 12 2f 27 fd a6  |546......B../'..|
00000190  14 17 17 14 02 12 39 03  17 02 ea 0d 11 82 1e 30  |......9........0|
000001a0  17 26 26 2b 1c 1b 2b 6a  06 06 0e 1d 00 01 00 00  |.&&+..+j........|
000001b0  00 03 01 81 00 2a 00 00  00 00 00 02 00 04 00 20  |.....*......... |
000001c0  00 60 00 60 01 00 00 08  00 00 00 00 00 00 00 00  |.`.`............|
000001d0  00 28 00 50 00 01 00 00  00 01 00 00 d9 4e b0 17  |.(.P.........N..|
000001e0  5f 0f 3c f5 00 03 03 e8  00 00 00 00 dc 01 d1 d8  |_.<.............|
000001f0  00 00 00 00 dc 01 d4 c2  ff 7e fe 1c 05 36 03 d4  |.........~...6..|
00000200  00 00 00 09 00 02 00 00  00 00 00 00 03 e8 00 fa  |................|
00000210  02 56 00 5c 03 e8 00 78  00 01 00 00 03 d4 fe 1c  |.V.\...x........|
00000220  00 00 05 4e ff 7e ff 4c  05 36 00 01 00 00 00 00  |...N.~.L.6......|
00000230  00 00 00 00 00 00 00 00  00 00 00 03 00 04 03 d8  |................|
00000240  01 90 00 05 00 08 02 8a  02 58 00 00 00 4b 02 8a  |.........X...K..|
00000250  02 58 00 00 01 5e 00 32  01 31 00 00 00 02 06 00  |.X...^.2.1......|
00000260  04 01 01 01 01 01 00 00  00 01 00 00 00 00 00 00  |................|
00000270  00 00 00 00 00 00 48 4e  59 49 01 40 00 31 00 31  |[email protected]|
00000280  03 20 ff 38 00 00 03 d4  01 e4 00 04 00 9f 00 00  |. .8............|
00000290  00 00 01 fd 02 b7 00 00  00 20 00 01 00 00 00 02  |......... ......|
000002a0  00 00 00 03 00 00 00 14  00 03 00 01 00 00 00 14  |................|
000002b0  00 04 00 20 00 00 00 04  00 04 00 01 00 00 00 31  |... ...........1|
000002c0  ff ff 00 00 00 31 ff ff  ff d0 00 01 00 00 00 00  |.....1..........|
000002d0  b8 01 ff 85 b8 00 04 8d  00 00 00 07 00 5a 00 03  |.............Z..|
000002e0  00 01 04 09 00 00 00 74  00 00 00 03 00 01 04 09  |.......t........|
000002f0  00 01 00 14 00 74 00 03  00 01 04 09 00 02 00 0e  |.....t..........|
00000300  00 88 00 03 00 01 04 09  00 03 00 3c 00 96 00 03  |...........<....|
00000310  00 01 04 09 00 04 00 14  00 74 00 03 00 01 04 09  |.........t......|
00000320  00 05 00 18 00 d2 00 03  00 01 04 09 00 06 00 14  |................|
00000330  00 ea 00 28 00 63 00 29  00 20 00 43 00 6f 00 70  |...(.c.). .C.o.p|
00000340  00 79 00 72 00 69 00 67  00 68 00 74 00 20 00 42  |.y.r.i.g.h.t. .B|
00000350  00 65 00 69 00 6a 00 69  00 6e 00 67 00 20 00 48  |.e.i.j.i.n.g. .H|
00000360  00 61 00 6e 00 79 00 69  00 20 00 49 00 6e 00 6e  |.a.n.y.i. .I.n.n|
00000370  00 6f 00 76 00 61 00 74  00 69 00 6f 00 6e 00 20  |.o.v.a.t.i.o.n. |
00000380  00 54 00 65 00 63 00 68  00 6e 00 6f 00 6c 00 6f  |.T.e.c.h.n.o.l.o|
00000390  00 67 00 79 00 20 00 43  00 6f 00 2e 00 2c 00 4c  |.g.y. .C.o...,.L|
000003a0  00 74 00 64 00 2e 00 48  00 59 00 43 00 75 00 59  |.t.d...H.Y.C.u.Y|
000003b0  00 75 00 61 00 6e 00 20  00 4a 00 52 00 65 00 67  |.u.a.n. .J.R.e.g|
000003c0  00 75 00 6c 00 61 00 72  00 48 00 61 00 6e 00 79  |.u.l.a.r.H.a.n.y|
000003d0  00 69 00 20 00 48 00 59  00 43 00 75 00 59 00 75  |.i. .H.Y.C.u.Y.u|
000003e0  00 61 00 6e 00 2d 00 4a  00 20 00 52 00 65 00 67  |.a.n.-.J. .R.e.g|
000003f0  00 75 00 6c 00 61 00 72  00 20 00 76 00 36 00 2e  |.u.l.a.r. .v.6..|
00000400  00 30 00 30 00 56 00 65  00 72 00 73 00 69 00 6f  |.0.0.V.e.r.s.i.o|
00000410  00 6e 00 20 00 36 00 2e  00 30 00 30 00 48 00 59  |.n. .6...0.0.H.Y|
00000420  00 43 00 75 00 59 00 75  00 61 00 6e 00 2d 00 4a  |.C.u.Y.u.a.n.-.J|
00000430  00 03 00 00 00 00 00 00  ff b5 00 32 00 00 00 00  |...........2....|
00000440  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
00000450  00 01 00 01 ff ff 00 0a  00 01 00 00 00 0a 00 1c  |................|
00000460  00 1e 00 01 44 46 4c 54  00 08 00 04 00 00 00 00  |....DFLT........|
00000470  ff ff 00 00 00 00 00 00  00 01 00 00 00 0a 00 5c  |...............\|
00000480  00 ca 00 04 44 46 4c 54  00 1a 63 79 72 6c 00 28  |....DFLT..cyrl.(|
00000490  67 72 65 6b 00 36 6c 61  74 6e 00 44 00 04 00 00  |grek.6latn.D....|
000004a0  00 00 ff ff 00 02 00 00  00 04 00 04 00 00 00 00  |................|
000004b0  ff ff 00 02 00 01 00 05  00 04 00 00 00 00 ff ff  |................|
000004c0  00 02 00 02 00 06 00 04  00 00 00 00 ff ff 00 02  |................|
000004d0  00 03 00 07 00 08 76 65  72 74 00 32 76 65 72 74  |......vert.2vert|
000004e0  00 38 76 65 72 74 00 40  76 65 72 74 00 48 76 72  |[email protected]|
000004f0  74 32 00 50 76 72 74 32  00 56 76 72 74 32 00 5e  |t2.Pvrt2.Vvrt2.^|
00000500  76 72 74 32 00 66 00 00  00 01 00 00 00 00 00 02  |vrt2.f..........|
00000510  00 00 00 02 00 00 00 02  00 00 00 01 00 00 00 02  |................|
00000520  00 00 00 03 00 00 00 01  00 04 00 00 00 02 00 04  |................|
00000530  00 06 00 00 00 02 00 04  00 05 00 00 00 02 00 04  |................|
00000540  00 07 00 08 00 12 00 12  00 12 00 12 00 12 00 12  |................|
00000550  00 12 00 12 00 01 00 00  00 01 00 08 00 01 00 06  |................|
00000560  00 01 00 01 00 01 00 01  03 e8 00 96 00 95 00 29  |...............)|
00000570  00 01 00 00 01 f4 fe 0c  00 00 03 e8 ff 4c fe e4  |.............L..|
00000580  03 20 00 00 00 01 00 00  00 00 00 00 00 00 00 00  |. ..............|
00000590  00 00 00 01                                       |....|
00000594

标记序号	类型	名称	解释
1	uint32	scalerType	0x74727565（true）和0x00010000都表示TTF格式
2	uint16	numTables	表数量
3	uint16	searchRange	搜索范围 (maximum的二次幂<=numTables)*16
4	uint16	entrySelector	条目选择器 log2(maximum的二次幂<=numTables)
5	uint16	rangeShift	范围偏移 (numTables*16-searchRange)
6、10	uint32	tag	4字节标识符
7	uint32	checkSum	校验和
8	uint32	offset	从sfnt的偏移量
9	uint32	length	表长度(字节长度)

tag : 0x47504f53 = GPOS
checkSum : 0x44764c75
offset : 0x00000458 = 1112
length : 0x00000020 = 32
GPOS的表格内容从1112的位置开始，总长度32，具体内容需要根据GPOS表格规则解析

参考内容

TrueTypeFont 维基百科

Apple 字体表

TTF字体格式入门 LiangJ