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diff --git a/doc/context/presentations/context/2021/context-2021-compactfonts.tex b/doc/context/presentations/context/2021/context-2021-compactfonts.tex new file mode 100644 index 000000000..7d2d3e482 --- /dev/null +++ b/doc/context/presentations/context/2021/context-2021-compactfonts.tex @@ -0,0 +1,609 @@ +% 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 |