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$Integrating TEX, MetaPost, JavaScript and PDF - Pragma ADE$

10 Font formats When T E X ships out a page, the backend will load the real font data and merge that into the final output. It will now take the glyph index and build the right data structures and references to the real font. As a font gets subset only the used glyphs end up in the final output. There is one tricky aspect involved here: re-encoding. In so called map files one can map a specific metric filename onto a real font name. One can also specify an encoding vector that tells what a given index really refers to. This makes it possible to use fonts that have more than 256 glyphs and refer to any of them. This is also the trick that makes it possible to use TrueType fonts in pdfT E X: the backend code filters the right glyphs from the font, remapping T E X’s glyph indices onto real entries in the font happens via the encoding vector. In figure 1.6 we show a possible route for input byte 68. bytes (68) bytes (31) index (31) index (88) Figure 1.6 From bytes to indices. As LuaT E X carries much of the bagage of older engines, you can still do it this way but in ConT E Xt MkIV we have made our live much simpler: we use unicode as much as possible. This means that we effectively have removed two steps (see figure 1.7). input glyphs Figure 1.7 Simplified mapping in LuaT E X. There is of course still some work to do for the backend, like subsetting, but the nasty dependency on the input encoding, font encoding (that itself relates to hyphenation) and backend re-encoding is gone. But keep in mind that the internal data structure of the font is still quite traditional. Before we move on to font formats I like to point out that there is no space in T E X. Spaces in the input are converted into glue, either or not with some stretch and/or shrink. This also means that accessing character 32 in traditional T E X will not end up as space in the output. 1.4 T E X metrics A.2 A.1 Traditional font metrics are packaged in a binary format. Due to the limitations of that time a font has at most 256 characters. In books dedicated to T E X you will often find tables that show what glyphs are in a font, so we will not repeat that here as after all we got rid of that limitation in LuaT E X. Because 256 is not that much, especially when you mix many scripts and need lots of symbols from the same font, there are quite some encodings used in traditional T E X, like texnansi, ec and qx. When you use LuaT E X exclusively you can do with way less font files. This is easier for users, especially because most of those files were never used
anyway. It’s interesting to notice that some of the encodings contain symbols that are never used or used only once in a document, like the copyright or registered symbols. They are often accessed by symbolic names and therefore easily could have been omitted and collected in a dedicated symbol font thereby freeing slots for more useful characters anyway. The lack of coverage is probably one of the reasons why new encodings kept popping up. In the next table you see how many files are involved in Latin Modern which comes in a couple of design sizes. 2 font format type # files size in bytes ConT E Xt type 1 tfm 380 3.841.708 afm 25 2.697.583 pfb 92 9.193.082 enc 15 37.605 map 9 42.040 521 15.812.018 mkii opentype otf 73 8.224.100 mkiv A tfm file can contain so called italic corrections. This is an additional kern that can be added after a character in order to get better spacing between an italic shape and an upright one. As this is manual work, it’s a not that advanced mechanism, but in addition to width, height, depth, kerns and ligatures it is nevertheless a useful piece of information. But, it’s a rather T E X specific quantity. Since T E X showed up many fonts have been added. In addition support for commercial fonts was provided. In fact, for that to happen, one only needs accompanying metric files for T E X itself and map files and encoding vectors for the backend. Because a metric file also has some general information, like spacing (including stretch and shrink), the ex-height and em-width, this means that sometimes guesses must be made when the original font does not come with such parameters. At some point virtual fonts were introduced. In a virtual font a tfm file has an accompanying vf file. In that file each glyph has a specification that tells where to find the real glyph. It is even possible to construct glyphs from other glyphs. In traditional T E X this only concerns the backend, which in pdfT E X is built in. In LuaT E X this mechanism is integrated into the frontend which means that users can construct such virtual fonts themselves. We will see more of that later, but for now it’s enough to know that when we talk about the representation of font (the tfm table) in LuaT E X, this includes virtual functionality. An important limitation of tfm files cq. traditional T E X is that the number of depths and heights is limited to 16 each. Although this results in somewhat inaccurate dimensions in practice this gets unnoticed, if only because many designs have some consistency in this. On the other hand, it is a limitation when we start thinking of accents or even 2 The original Computer Modern fonts have METAFONT source files and (runtime) generated bitmap files in whatever resolutions are needed for previewing and printing. The Type1 follow-up came in several sets, organized by language support. The Latin Modern fonts have a few more weights and variants than Computer Modern. 11 Font formats
Page 1: explaining luatex and mkiv Fonts ou
Page 4 and 5: 2 Contents 5.4 Goodies 73 5.5 Analy
Page 6 and 7: 4 Contents
Page 8 and 9: 6 Introduction In this manual we wi
Page 10 and 11: 8 Font formats a b g l q . ; ? ffi
Page 14 and 15: 12 A.4 A.3 Font formats multiple ac
Page 16 and 17: 14 Font formats can be rules that t
Page 18 and 19: 16 Font formats /fonts/tfm/vendor/t
Page 20 and 21: 18 Modes raw tfm normalized tfm raw
Page 22 and 23: 20 Modes shown next: kern cyrl dflt
Page 24 and 25: 22 Modes ccmp cyrl mkd абвгде
Page 26 and 27: 24 Modes dlig latn gag abcdefghijkl
Page 28 and 29: 26 Modes liga latn nsm abcdefghijkl
Page 30 and 31: 28 Modes salt latn mol abcdefghijkl
Page 32 and 33: 30 Modes glyph 256 font 42: U+00074
Page 38 and 39: 36 Modes optimizer that can apply a
Page 40 and 41: 38 Modes ا خǇَ﮲ ف﮲َ step
Page 42 and 43: 40 Modes dir +TRT glyph 256 font 49
Page 44 and 45: 42 Modes and now we get: 123 normal
Page 46 and 47: 44 Modes MkIV run can be faster tha
Page 48 and 49: 46 Lookups \font \MyFontG = lmr12 s
Page 50 and 51: 48 Lookups 3.4 Name Say that we wan
Page 52 and 53: 50 Lookups We add another specifier
Page 54 and 55: 52 Methods \definefont [MyFont] [Bo
Page 56 and 57: 54 Methods } copyright = "ConTeXt d
Page 58 and 59: 56 Features of all, all we get to s
Page 60 and 61: 58 Features in base mode. A single
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60 Features accumulate within a wor
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62 Features features analyze=yes, c
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64 Features \definedfont[lmroman10-
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66 Features single substitutions or
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68 F -0.492 eatures result ffi feat
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70 Features font 80: lmroman10-regu
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72 Features font 46: cambria.ttf @
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74 Features } } This goodie file is
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76 Features { name = "msbm10.tfm",
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78 Features \starttypescript[somefo
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80 Features \setupbodyfont [mojcasf
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82 Features } normalweight = "extra
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84 Features "QF.waqf", "SKTH.waqf",
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86 Features featureset=smallcaps] O
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88 Features } }, When defining the
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90 Features local defaultfraction =
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92 Features } } ["LMRoman-Bold"] =
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94 Features In fact, in addition to
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96 Features } This time the applica
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98 Features step 1 I don't wanna kn
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100 Features If you’re lucky your
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102 Scripts
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However, when we go the other way,
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122 Math the regular a--z character
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While there are lots of text fonts,
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8 Extensions 8.1 Introduction One o
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[default] [itlc=5] This is demonstr
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132 Extensions \definefontfeature [
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134 Extensions characters to improv
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136 Extensions U+00079 0.05 y 0.05
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138 Extensions protrusion classes T
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140 Extensions [fonts.composing.def
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142 } Extensions top = { x = -250,
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144 Extensions
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146 Hooks
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148 ) Appendix (LIG C l O 10) (KRN
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150 ) Appendix (KRN O 177 R 0.056)
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152 Appendix Notice Copyright 2003-
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154 Appendix ... KPX seven.prop hyp
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156 Appendix name = , features = ,
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158 Appendix [] = "", ... default =
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160 Appendix A.10 Discretionary nod
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