% language=us \usemodule[present-boring,abbreviations-logos] \definehighlight[nb][style=bold,color=middlegray,define=no] \definecolor[maincolor][g=.3] \startdocument [title={COMPACT FONTS}, banner={a different approach to scaling}, location={context\enspace {\bf 2021}\enspace meeting}] \starttitle[title=How \TEX\ uses fonts] \startitemize \startitem In a \TEX\ engine there is a 1-to-1 mapping from characters in the input to a slot in a font. \stopitem \startitem Combinations of characters can be mapped onto one shape: ligatures. \stopitem \startitem Hyphenation is (also) controlled by the input encoding of a font which imposes some limitations. \stopitem \startitem In the typeset result characters (glyphs) can be (re)positioned relatively: kerns. \stopitem \startitem This all happens in a very interwoven way (e.g. inside the par builder). \stopitem \stopitemize \stoptitle \starttitle[title=How traditional \TEX\ sees fonts] \startitemize \startitem A font is just a (binary) blob of data with information where characters have a width, height, depth and italic correction. \stopitem \startitem The engine only needs the dimensions and when the same font is used with a different scale a copy with scaled dimensions is used. \stopitem \startitem There can be recipes for ligatures and (more complex) so called math extensible shapes (like arrows, wide accents, fences and radicals) \stopitem \startitem There are pairwise specification for kerning. \stopitem \startitem A handful of font parameters is provided in order to control for instance spacing. \stopitem \startitem Virtual fonts are just normal fonts but they have recipes for the backend to construct shapes: \TEX\ uses the normal metric file, the backend also the virtual specification file. \stopitem \stopitemize \blank[2*big] An example of a definition and usage: \starttyping \font\cs somename [somescale] test {\cs test} test \stoptyping \stoptitle \starttitle[title=\UNICODE\ engines] \startitemize \startitem There are no fundamental differences between a traditional engine and an \UNICODE\ aware one with respect to what \TEX\ needs from fonts: dimensions. \stopitem \startitem There can be more than 256 characters in a font. \stopitem \startitem Some mechanisms have to be present for applying font features (like ligaturing and kerning). \stopitem \startitem In \LUATEX\ hyphenation, ligaturing and kerning are clearly separate steps. \stopitem \startitem In \LUATEX\ callbacks can do lots of things with fonts and characters. \stopitem \startitem Math fonts are handled differently and there is more info that comes from the font. \stopitem \startitem In \LUATEX\ features like expansion are implemented differently, i.e.\ no copies of fonts are made and applied expansion travels with the glyphs. \stopitem \stopitemize \stoptitle \starttitle[title=Overhead] \startitemize \startitem In all engines scales copies are used. For traditional \TEX\ a copy is cheap, but a font that supports more of \UNICODE\ cna be quite large. \stopitem \startitem Different feature sets in principle make for a different font (this can be different per macro package). \stopitem \startitem Every math scale needs three font instances: text, script and scriptscript. \stopitem \startitem In \CONTEXT\ lots of sharing takes place and a lot of low level optimizations happens (memory, performance). We always made sure (already in \MKII) that the font system was not the bottleneck. \stopitem \startitem In most cases font definitions are dynamic, and we delay initialization as much as possible. \stopitem \startitem In \MKIV\ font features can be dynamic which saves a lot of memory at the cost of some extra processing overhead. \stopitem \stopitemize \stoptitle \starttitle[title=Design sizes] \startitemize \startitem A macro package's font handling is complicated by design sizes. The low level code can look complex too. \stopitem \startitem There are hardly any fonts that come in design sizes (basically only Computer Modern) so we need to support that. \stopitem \startitem Design sizes make sense for math fonts where very small characters and symbols are used in scripts. \stopitem \startitem In \OPENTYPE\ fonts smaller math design sizes are part of the font (that then gets loaded three times with different \type {ssty} settings). \stopitem \stopitemize \startlinecorrection \dontleavehmode\scale[frame=on,height=5ex]{$\textstyle 2$}\quad \dontleavehmode\scale[frame=on,height=5ex]{$\scriptstyle 2$}\quad \dontleavehmode\scale[frame=on,height=5ex]{$\scriptscriptstyle 2$}\quad\quad \dontleavehmode\scale[frame=on,height=2ex]{$\textstyle 2$}\quad \dontleavehmode\scale[frame=on,height=2ex]{$\scriptstyle 2$}\quad \dontleavehmode\scale[frame=on,height=2ex]{$\scriptscriptstyle 2$}\quad\quad \dontleavehmode\scale[frame=on,width=4em]{\colored[r=.6,a=1,t=.5]{$\textstyle 2$}}\hskip-4em \dontleavehmode\scale[frame=on,width=4em]{\colored[g=.6,a=1,t=.5]{$\scriptstyle 2$}}\hskip-4em \dontleavehmode\scale[frame=on,width=4em]{\colored[b=.6,a=1,t=.5]{$\scriptscriptstyle 2$}}\quad\quad \dontleavehmode{$\textstyle 2$}\quad \dontleavehmode{$\scriptstyle 2$}\quad \dontleavehmode{$\scriptscriptstyle 2$}\quad \stoplinecorrection \stoptitle \starttitle[title=The system] \startitemize \startitem Each bodyfont size (often a few are defined) has regular, bold, italic, bold italic, slanted, bold slanted, etc. There can be unscaled instances (design size) or scaled ones. \stopitem \startitem Within a bodyfont size we have size variants: smaller {\tx x} and {\tx xx}, larger {\tfa a}, {\tfb b}, {\tfc c} and {\tfd d}. \stopitem \startitem In \MKII\ we inherit smallcap and oldstyle setups but in \MKIV\ one can either do that dynamic or define an additional bodyfont instance. \stopitem \startitem A document can use a mix of fonts mixed setup, so there is a namespace used per family. \stopitem \startitem In \OPENTYPE\ symbols are more naturally part of a font, as are emoji and colored shapes. \stopitem \startitem Lack of variants can result in artificially slanted of boldened fonts (more advanced in \MKIV). Variable fonts are not special, but demand some work when loading and embedding. \stopitem \startitem Runtime virtual fonts are part of \MKIV\ as are fallback shapes. \stopitem \startitem Languages and scripts can introduce an extra dimension to operate on. \stopitem \startitem Math is greatly simplified by the fact that families are part of a font. \stopitem \startitem Bold math fonts are provided by the boldening feature. \stopitem \stopitemize \stoptitle \starttitle[title={Practice}] \startitemize \startitem Due to optimizations the actual number of loaded instances is normally small but there are exceptions. \stopitem \startitem The \LUAMETATEX\ manual has 158 instances most of which are math (six per used bodyfont for math plus a regular: Lucida, Pagella, Latin Modern, Dejavu, Cambria). \stopitem \startitem The final \PDF\ file has 21 embedded fonts (subsets). \stopitem \startitem The fact that different sizes each have an instance and that for math we need three per size plus one for r2l, while the only difference is scale, makes one think of other solutions. \stopitem \startitem Using duplicates of huge \CJK\ fonts makes it even more noticeable. \stopitem \stopitemize But there is a way out! \stoptitle \starttitle[title=Glyph scaling] We can scale glyphs in three ways: \startbuffer \definedfont[lmroman10-regular*default]% test {\glyphxscale 2500 test} test test {\glyphyscale 2500 test} test test {\glyphscale 2500 test} test \stopbuffer \typebuffer {\getbuffer} We do need to honor grouping: \startbuffer \definedfont[lmroman10-regular*default]% e{\glyphxscale 2500 ff}icient ef{\glyphxscale 2500 f}icient ef{\glyphxscale 2500 fi}cient e{\glyphxscale 2500 ffi}cient \stopbuffer \typebuffer {\getbuffer} These scales can also be part of a font definition so we can do with less instances. \stoptitle \starttitle[title=Implications] \startitemize \startitem The text processing part of the engine has to scale on the fly (e.g.\ when dimensions are needed in paragraph building and (box) packing. \stopitem \startitem Font processing (features) already distinguishes per instance but now also has to differentiate by (upto three) scales (we use the same font id for scaled instances). \stopitem \startitem The math machinery has to check for smaller sizes and also scale dimensions on the fly. \stopitem \startitem For math that means two times scaling: the main scale (like glyph scale) plus the relative scaling of script and scriptscript. \stopitem \startitem When they are used font dimensions and math parameters are to be scaled as are rules in some math extensibles. \stopitem \startitem This all has to be done efficiently so that there is no significant drop in performance. \stopitem \startitem But quite a bit less memory is used and loading time has become less too. \stopitem \stopitemize Some day this will become default (which means a sentimental process of dropping ancient code): \starttyping \enableexperiments[fonts.compact] \stoptyping \stoptitle \starttitle[title=Details] The tricks shown on this page and following pages have been in place and tested for a while now. Because \TEX\ uses integers a scale value of 1000 means 1.000, as in other mechanisms: \startbuffer \definedfont[lmroman10-regular*default]% test {\glyphscale 2500 test} test \stopbuffer \typebuffer {\getbuffer} % \glyphtextscale % \glyphscriptscale % \glyphscriptscriptscale \page The font definition mechanism supports horizontal and vertical scaling: \startbuffer \definefont[FooA][Serif*default @ 12pt 1800 500] \definefont[FooB][Serif*default @ 12pt 0.85 0.4] \definefont[FooC][Serif*default @ 12pt] There is also a new command: \definetweakedfont[runwider] [xscale=1.5] \definetweakedfont[runtaller][yscale=2.5,xscale=.8,yoffset=-.2ex] {\FooA test test \runwider test test \runtaller test test}\par {\FooB test test \runwider test test \runtaller test test}\par {\FooC test test \runwider test test \runtaller test test}\par \stopbuffer \typebuffer \getbuffer \page Tweaking also works in math: \startbuffer \definetweakedfont[squeezed][xscale=0.9] \definetweakedfont[squoozed][xscale=0.7] \startlines $a = b^2 + \sqrt{c}$ {\squeezed $a = b^2 + \sqrt{c}$} {\squoozed $a = b^2 + \sqrt{c}$} {$\squoozed a = b^2 + \sqrt{c}$} {$\scriptstyle a = b^2 + \sqrt{c}$} \stoplines \stopbuffer \typebuffer \getbuffer \page \startbuffer \startcombination[3*1] {\bTABLE \bTR \bTD foo \eTD \bTD[style=\squeezed] $x = 1$ \eTD \eTR \bTR \bTD oof \eTD \bTD[style=\squeezed] $x = 2$ \eTD \eTR \eTABLE} {local} {\bTABLE[style=\squeezed] \bTR \bTD $x = 1$ \eTD \bTD $x = 3$ \eTD \eTR \bTR \bTD $x = 2$ \eTD \bTD $x = 4$ \eTD \eTR \eTABLE} {global} {\bTABLE[style=\squeezed\squeezed\squeezed\squeezed] \bTR \bTD $x = 1$ \eTD \bTD $x = 3$ \eTD \eTR \bTR \bTD $x = 2$ \eTD \bTD $x = 4$ \eTD \eTR \eTABLE} {multiple} \stopcombination \stopbuffer \typebuffer \startlinecorrection \getbuffer \stoplinecorrection \page Tweaking can be combined with styles: \startbuffer \definetweakedfont[MyLargerFontA][scale=2000,style=bold] test {\MyLargerFontA test} test \stopbuffer \typebuffer \getbuffer \page We can use negative scale values: \startbuffer \bTABLE[align=middle] \bTR \bTD a{\glyphxscale 1000 \glyphyscale 1000 bc}d \eTD \bTD a{\glyphxscale 1000 \glyphyscale -1000 bc}d \eTD \bTD a{\glyphxscale -1000 \glyphyscale -1000 bc}d \eTD \bTD a{\glyphxscale -1000 \glyphyscale 1000 bc}d \eTD \eTR \bTR \bTD \tttf +1000 +1000 \eTD \bTD \tttf +1000 -1000 \eTD \bTD \tttf -1000 -1000 \eTD \bTD \tttf -1000 +1000 \eTD \eTR \eTABLE \stopbuffer \typebuffer \startlinecorrection \getbuffer \stoplinecorrection \page There are more glyph properties: \startbuffer \ruledhbox{ \ruledhbox{\glyph yoffset 1ex options 0 123} % left curly brace \ruledhbox{\glyph xoffset .5em yoffset 1ex options "C0 123} \ruledhbox{oeps{\glyphyoffset 1ex \glyphxscale 800 \glyphyscale\glyphxscale oeps}oeps} } \stopbuffer \typebuffer \scale[width=\textwidth]{\getbuffer} \page Glyph scales are internal counter values, like any other: \startbuffer \samplefile{jojomayer} {\glyphyoffset .8ex \glyphxscale 700 \glyphyscale\glyphxscale \samplefile{jojomayer}} {\glyphyscale\numexpr3*\glyphxscale/2\relax \samplefile{jojomayer}} {\glyphyoffset -.2ex \glyphxscale 500 \glyphyscale\glyphxscale \samplefile{jojomayer}} \samplefile{jojomayer} \stopbuffer \typebuffer \getbuffer \page There is a helper for real (float) scales: \startbuffer 1200 : \the\numericscale1200 1.20 : \the\numericscale1.200 \stopbuffer \typebuffer These lines produce the same integer: \startlines\tttf \getbuffer \stoplines \page You can do this but it's not always predictable (depends on outer scales too): \startbuffer[definition] \def\UnKernedTeX {T% {\glyph xoffset -.2ex yoffset -.4ex `E}% {\glyph xoffset -.4ex options "60 `X}} \stopbuffer \startbuffer[example] We use \UnKernedTeX\ and {\bf \UnKernedTeX} and {\bs \UnKernedTeX}: the slanted version could use some more left shifting of the E. \stopbuffer \typebuffer[definition,example] \startnarrower \getbuffer[definition,example] \stopnarrower Marks and cursive features can interfere, so this is an alternative: \startbuffer[definition] \def\UnKernedTeX {T\glyph left .2ex raise -.4ex `E\glyph left .2ex `X\relax} \stopbuffer \typebuffer[definition] \startnarrower \getbuffer[definition,example] \stopnarrower \page Yet another glyph option: \starttyping \multiply\glyphscale by 2 <{\darkgray \glyph `M}> \multiply\glyphscale by 2 <{\darkgray \glyph raise 3pt `M}> \multiply\glyphscale by 2 <{\darkgray \glyph raise -3pt `M}> \multiply\glyphscale by 2 <{\darkgray \glyph left 3pt `M}> \multiply\glyphscale by 2 <{\darkgray \glyph right 2pt `M}> \multiply\glyphscale by 2 <{\darkgray \glyph left 3pt right 2pt `M}> \multiply\glyphscale by 2 <{\darkgray \glyph left -3pt `M}> \multiply\glyphscale by 2 <{\darkgray \glyph right -2pt `M}> \multiply\glyphscale by 2 <{\darkgray \glyph left -3pt right -2pt `M}> \stoptyping \startlinecorrection \bTABLE[align=middle,width=.33\textwidth] \bTR \bTD \showglyphs \multiply\glyphscale by 2 <{\darkgray \glyph `M}>\eTD \bTD \showglyphs \multiply\glyphscale by 2 <{\darkgray \glyph raise 3pt `M}>\eTD \bTD \showglyphs \multiply\glyphscale by 2 <{\darkgray \glyph raise -3pt `M}>\eTD \eTR \bTR[frame=off] \bTD \tttf \eTD \bTD \tttf raise 3pt \eTD \bTD \tttf raise -3pt \eTD \eTR \bTR \bTD \showglyphs \multiply\glyphscale by 2 <{\darkgray \glyph left 3pt `M}>\eTD \bTD \showglyphs \multiply\glyphscale by 2 <{\darkgray \glyph right 2pt `M}>\eTD \bTD \showglyphs \multiply\glyphscale by 2 <{\darkgray \glyph left 3pt right 2pt `M}>\eTD \eTR \bTR[frame=off] \bTD \tttf left 3pt \eTD \bTD \tttf right 2pt\eTD \bTD \tttf left 3pt right 2pt\eTD \eTR \bTR \bTD \showglyphs \multiply\glyphscale by 2 <{\darkgray \glyph left -3pt `M}>\eTD \bTD \showglyphs \multiply\glyphscale by 2 <{\darkgray \glyph right -2pt `M}>\eTD \bTD \showglyphs \multiply\glyphscale by 2 <{\darkgray \glyph left -3pt right -2pt `M}>\eTD \eTR \bTR[frame=off] \bTD \tttf left -3pt \eTD \bTD \tttf right -2pt \eTD \bTD \tttf left -3pt right -2pt \eTD \eTR \eTABLE \stoplinecorrection \page A larger example: \startbuffer \glyphscale 4000 \vl\glyph `M\vl\quad \vl\glyph raise .2em `M\vl\quad \vl\glyph left .3em `M\vl\quad \vl\glyph right .2em`M\vl\quad \vl\glyph left -.2em right -.2em`M\vl\quad \vl\glyph raise -.2em right .4em`M\vl \stopbuffer \typebuffer {\getbuffer} \stoptitle \stopdocument