diff options
Diffstat (limited to 'doc/context/presentations/bachotex/2016/bachotex-2016-opentype.tex')
| -rw-r--r-- | doc/context/presentations/bachotex/2016/bachotex-2016-opentype.tex | 631 |
1 files changed, 631 insertions, 0 deletions
diff --git a/doc/context/presentations/bachotex/2016/bachotex-2016-opentype.tex b/doc/context/presentations/bachotex/2016/bachotex-2016-opentype.tex new file mode 100644 index 000000000..aa9cb60fd --- /dev/null +++ b/doc/context/presentations/bachotex/2016/bachotex-2016-opentype.tex @@ -0,0 +1,631 @@ +\usemodule[present-banner] + +\startdocument + [title={OPENTYPE FONTS}, + subtitle={the generic loader}, + location={Hans Hagen \endash\ bacho\TeX\ 2016}] + +\starttitle[title={how engines sees a font}] + +\startsubject[title={\TeX}] + + \highlight [nb] {fields:} width, height, depth, italic correction, kern table, + ligature tree, vf commands, next size pointer, extensible specification + \highlight [nb] {and} a set of text and math parameters + +\stopsubject + +\startsubject[title={\pdfTeX}] + + \highlight [nb] {extra fields:} left protruding, right protruding, expansion + factor \highlight [nb] {and} parameters to control these + +\stopsubject + +\startsubject[title={\LuaTeX}] + + \highlight [nb] {extra fields:} math top accent, math bot accent, tounicode, + adapted extensible specification, vertical variants, horizontal variants, + name, index, used status, math kerns \highlight [nb] {and} extra parameters + \highlight [nb] {and} math constants \highlight [nb] {and} no 8~bit + limitations + +\stopsubject + +\startsubject[title={\XeTeX}] + + probably something similar + +\stopsubject + +\stoptitle + +\starttitle[title={font handling}] + +\startsubject[title={loading opentype font data}] + + \startitemize + \startitem + till recently we used the built|-|in fontforge loader library + \stopitem + \startitem + but now we use a recently written \Lua\ loader + \stopitem + \startitem + but use a similar feature handler + \stopitem + \startitem + in \ConTeXt\ one can fall back to the old loader/handler + \stopitem + \stopitemize + +\stopsubject + +\startsubject[title={applying (opentype) features}] + + \highlight [nb] {generic modes:} base, node \crlf + \highlight [nb] {\ConTeXt\ modes:} base, node, auto, dynamic + +\stopsubject + +\startsubject[title={locating (opentype) fonts}] + + \startitemize + \startitem + \highlight [nb] {file}: kpse in generic, resolvers in \ConTeXt + \stopitem + \startitem + \highlight [nb] {name}: simple in generic, extended in \ConTeXt, + different in \LaTeX + \stopitem + \startitem + \highlight [nb] {spec}: not in generic (uses font database) + \stopitem + \startitem + \highlight [nb] {virtual}: not in generic + \stopitem + \startitem + \highlight [nb] {lua}: delegated to low level interfaces + \stopitem + \stopitemize + +\stopsubject + +\stoptitle + +\starttitle[title={preparations}] + +\startsubject[title={after loading}] + + \startitemize + \startitem + initialize format driven substitution + \stopitem + \startitem + initialize format driven positioning + \stopitem + \startitem + enable analysis of states/properties + \stopitem + \startitem + initialize additional data for engine (protrusion, expansion, extend, + slant) + \stopitem + \startitem + apply user or \TeX\ format extensions + \stopitem + \startitem + apply manipulations before and after loading + \stopitem + \startitem + (build virtual fonts) + \stopitem + \startitem + enable special script handlers (fuzzy side of opentype) + \stopitem + \startitem + pass metrics and some metadata to \TeX + \stopitem + \stopitemize + +\stopsubject + +\startsubject[title={benefit}] + + efficient access to all font properties for additional processing beforehand + or afterwards + +\stopsubject + +\stoptitle + +\starttitle[title={processing}] + +\startsubject[title={steps}] + + \startitemize + \startitem + (comes after hyphenation) + \stopitem + \startitem + first identifies to be handled modes + \stopitem + \startitem + normalization (in \ConTeXt) node list + \stopitem + \startitem + delegate handling to \TeX\ or \Lua + \stopitem + \startitem + when using \Lua\ features are applied in prescribed order: + substitution, positioning, etc. + \stopitem + \startitem + as last step positioning is finalized (left/right kern injection, + space kerning, anchoring, cursives) + \stopitem + \stopitemize + +\stopsubject + +\startsubject[title={remarks}] + + \startitemize + \startitem + efficient contextual analysis is|-|non trivial + \stopitem + \startitem + discretionaries need special care: ...pre ...replace... post... + \stopitem + \startitem + there is no real limit in extensions + \stopitem + \startitem + it's not too hard to inject experimental code + \stopitem + \startitem + so users can add their own features + \stopitem + \startitem + some day there may be alternative handlers + \stopitem + \stopitemize + +\stopsubject + +\stoptitle + +\starttitle[title={math}] + +\startsubject[title={format}] + + the opentype math specification stays close to \TeX, but has extensions and + more control (see articles & presentations by Ulrik Vieth) + +\stopsubject + +\startsubject[title={loading}] + + \startitemize + \startitem + maps more or less directly onto internal structures + \stopitem + \startitem + in \ConTeXt\ we use(d) virtual unicode fonts awaiting lm/gyre + \stopitem + \stopitemize + +\stopsubject + +\startsubject[title={processing}] + + character mapping and special element handling remains macro package + dependent + +\stopsubject + +\startsubject[title={construction}] + + \startitemize + \startitem + we split code paths when needed: traditional or opentype (no longer + heuristics) + \stopitem + \startitem + the \luaTeX\ engine provides much control over spacing and a bit more + over rendering + \stopitem + \stopitemize + +\stopsubject + +\stoptitle + +\starttitle[title={the basics of loading}] + +\startsubject[title={the format}] + + \startitemize + \startitem + it evolved out of competing formats by apple, microsoft and adobe + \stopitem + \startitem + two flavours can normally be recognized by suffix: \type {ttf} and + \type {otf} + \stopitem + \startitem + main differences are bounding box info, global kern tables, cubic vs + quadratic curves + \stopitem + \startitem + multiple sub fonts inside \type {ttc} files (font collections) + \stopitem + \startitem + it's considered a standard (so it should be possible to implement) + \stopitem + \stopitemize + +\stopsubject + +\startsubject[title={the specification}] + + \startitemize + \startitem + the only useable reference is on the microsoft website + \stopitem + \startitem + (the iso mpeg standard is more or less a bunch of ugly rendered + webpages) + \stopitem + \startitem + trial and error helps understanding/identifying fuzzy aspects + \stopitem + \stopitemize + +\stopsubject + +\stoptitle + +\starttitle[title={the available loaders}] + +\startsubject[title={the fontforge loader}] + + \startitemize + \startitem + offers the same view on the font as the editor (good for debugging) + \stopitem + \startitem + in order to process a font some optimal data structures are created + after loading + \stopitem + \startitem + we cache fonts because loading and creating these structures takes + time and it saves memory too + \stopitem + \startitem + fontforge has a lot of heuristics (catching issues collected over + time) but these are hard to get rid of when they're wrong + \stopitem + \stopitemize + +\stopsubject + +\startsubject[title={the lua loader}] + + \startitemize + \startitem + this started out as experiment for loading outlines in \MetaFun + \stopitem + \startitem + it avoids the conversion to optimal structures for handling + \stopitem + \startitem + we can hook in better heuristics (data is more raw) + \stopitem + \startitem + it fits in the wish for maximum flexibility (next stage \ConTeXt) + \stopitem + \startitem + it's rather trivial to extend and adapt without hard coding + \stopitem + \startitem + the performance can be a bit less on initial loading (pre|-|cache) + but there is a bit of room to improve + \stopitem + \startitem + it's much more efficient in identifying fonts (not a real issue in + practice) + \stopitem + \startitem + in practice most fonts behave ok (no recovery needed) but there are + some sloppy fonts around + \stopitem + \stopitemize + +\stopsubject + +\stoptitle + +\starttitle[title={what do we load}] + +\startsubject[title={tables}] + + \startitemize + \startitem + opentype is mostly tables with lots of subtables + \stopitem + \startitem + there are required, truetype outline, postscript outline, (svg and + bitmap), typography & additional ones + \stopitem + \startitem + the typographic tables specify transformations to apply (gdef, gsub, + gpos) + \stopitem + \stopitemize + +\stopsubject + +\startsubject[title={calculations}] + + \startitemize + \startitem + as we need ht/dp we need to calculate the boundingbox of postscript + outlines (cff parser) + \stopitem + \startitem + internally we use unicodes instead of indices + \stopitem + \startitem + we need to identify/filter the right unicode information + \stopitem + \startitem + we want to do more so we need to carry around more info (tounicode etc) + \stopitem + \stopitemize + +\stopsubject + +\startsubject[title={pitfalls}] + + \startitemize + \startitem + there is no real consistent approach to use of basic features: + single, one to multiple, multiple to one & many to many replacements, + and look ahead and/or back based solutions + \stopitem + \startitem + in principle consistent families like lm/gyre could share common data + and logic but otherwise there is much diversity around + \stopitem + \stopitemize + +\stopsubject + +\stoptitle + +\starttitle[title={a few details}] + +\startsubject[title={loading}] + + \startitemize + \startitem + load the file (subfont if needed) in a \Lua\ friendly format + \stopitem + \startitem + prepare for later processing and/or access + \stopitem + \startitem + optimize data structures + \stopitem + \startitem + cache the instance (and compile to bytecode) + \stopitem + \startitem + share loaded font data where possible + \stopitem + \startitem + initialize & mark enabled features + \stopitem + \startitem + pass metrics, parameters and some properties to \TeX + \stopitem + \stopitemize + +\stopsubject + +\startsubject[title={processing}] + + \startitemize + \startitem + we need to run over enabled features (also virtual non|-|opentype + ones) + \stopitem + \startitem + we use lookup hashes to determine if action is needed + \stopitem + \startitem + if needed we access detailed data and apply it + \stopitem + \startitem + there can be a few but also many hundreds of loops over the node list + \stopitem + \startitem + contextual matching can make us end up with a real lot of access and + analysis + \stopitem + \startitem + descending into discretionaries adds significant overhead (so it's + optimized) + \stopitem + \stopitemize + +\stopsubject + +\stoptitle + +\starttitle[title={traditional fonts}] + +\startsubject[title={tfm}] + + \startitemize + \startitem + there is a built|-|in loader for \type {tfm}, \type {ofm}, \type {vf} + and \type {ovf} files + \stopitem + \startitem + encoding and filename mapping is as usual (\type {enc} and \type + {map} files) + \stopitem + \startitem + (in the early days \ConTeXt\ filtered info from those \type {enc} + files too) + \stopitem + \stopitemize + +\stopsubject + +\startsubject[title={type one}] + + \startitemize + \startitem + type one fonts have their own loader that gets information from \type + {afm} files + \stopitem + \startitem + the \type {pfb} file is consulted to get the index (to unicode) + mapping + \stopitem + \startitem + the \type {afm} loader was already written in \Lua\ but we now can also use + \Lua\ for the \type {pfb} file + \stopitem + \stopitemize + +\stopsubject + +\stoptitle + +\starttitle[title={remarks}] + + \startitemize + \startitem + features like additional character kerning don't belong in the font + handler as they are (to some extent) macro package dependant + \stopitem + \startitem + the same is true for italic correction (often input related and + therefore a macro package specific issue) + \stopitem + \startitem + setting up protrusion and expansion is again somewhat macro package + dependent + \stopitem + \startitem + \ConTeXt\ has many extra font related mechanisms and features + (described in a more technical manual) + \stopitem + \blank + \startitem + this has to work well with the core subsystems: languages especially + hyphenators, specific script demands, typesetting (all kind), builders + (paragraph, page), etc. + \stopitem + \startitem + a complication is that we do this more and more in \Lua, but still need to + support the built|-|in mechanismsm too + \stopitem + \blank + \startitem + the interfacing to macro packages differs (for plain \TeX\ we use + code that ships with \ConTeXt) + \stopitem + \startitem + for bugs and issues of with fonts in \ConTeXt\ you use its mailing list (or + mail me) + \stopitem + \startitem + the \LaTeX\ interface is handled by Philipp Gesang + \stopitemize + +\stoptitle + +\starttitle[title={future}] + + \startitemize + \startitem + we'll improve handling of border cases (within the constraints of + performance) + \stopitem + \startitem + we might provide a few more hooks for plug|-|ins + \stopitem + \startitem + the type one \type {pfb} reader will be extended to provide outlines + (not complex, needed for \MetaFun) + \stopitem + \startitem + we keep playing with extra new features and virtual fonts + \stopitem + \blank + \startitem + maybe some more code can be made generic (fwiw) + \stopitem + \stopitemize + +\stoptitle + +\starttitle[title={credits}] + + \startitemize + \startitem + Kai Eigner and Ivo Geradts for (experimental) patches in the handlers + for rare, complex & creepy fonts + \stopitem + \startitem + Philipp Gesang for binding the generic code to \LaTeX\ font mechanims. + \stopitem + \startitem + Idris Samawi Hamid for testing and providing the very complex and + demanding Husayni font + \stopitem + \startitem + Hartmut Henkel for the initial cleaning up of expansion and protrusion + \stopitem + \startitem + Taco Hoekwater for the original loader and discussions and a lot more + \stopitem + \startitem + Boguslaw Jackowski and friends for the fonts and patience with us + \stopitem + \startitem + Dohyun Kim for testing and suggestions on CJK font support + \stopitem + \startitem + Mojca Miklavec for distributions, managing us, and basically everything + \stopitem + \startitem + Luigi Scarso for patiently testing and managing my patches and testing + very beta code + \stopitem + \startitem + Thomas Schmitz for using betas in deadline critital book production + and making sure we patch fast + \stopitem + \startitem + Ton Otten for permitting me to work on all this \TeX\ related stuff for + ever and ever (and using to the extreme) + \stopitem + \startitem + Wolfgang Schuster for knowing and testing every detail of \ConTeXt\ + and writing selectfont (for system fonts) + \stopitem + \blank + \startitem + and all (\ConTeXt) users who patiently accept betas and testing + \stopitem + \stopitemize + +\stoptitle + +\stopdocument |