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diff --git a/Master/texmf-dist/doc/context/sources/general/manuals/onandon/onandon-runtoks.tex b/Master/texmf-dist/doc/context/sources/general/manuals/onandon/onandon-runtoks.tex deleted file mode 100644 index b3adeb4a5db..00000000000 --- a/Master/texmf-dist/doc/context/sources/general/manuals/onandon/onandon-runtoks.tex +++ /dev/null @@ -1,531 +0,0 @@ -% language=uk - -\startcomponent onandon-amputating - -\environment onandon-environment - -\startchapter[title={Amputating code}] - -\startsection[title={Introduction}] - -Because \CONTEXT\ is already rather old in terms of software life and because it -evolves over time, code can get replaced by better code. Reasons for this can be: - -\startitemize[packed] -\startitem a better understanding of the way \TEX\ and \METAPOST\ work \stopitem -\startitem demand for more advanced options \stopitem -\startitem a brainwave resulting in a better solution \stopitem -\startitem new functionality provided in \TEX\ engine used \stopitem -\startitem the necessity to speed up a core process \stopitem -\stopitemize - -Replacing code that in itself does a good job but is no longer the best to be -used comes with sentiments. It can be rather satisfying to cook up a -(conceptually as well as codewise) good solution and therefore removing code from -a file can result in a somewhat bad feeling and even a feeling of losing -something. Hence the title of this chapter. - -Here I will discuss one of the more complex subsystems: the one dealing with -typeset text in \METAPOST\ graphics. I will stick to the principles and not -present (much) code as that can be found in archives. This is not a tutorial, -but more a sort of wrap|-|up for myself. It anyhow show the thinking behind -this mechanism. I'll also introduce a new \LUATEX\ feature here: subruns. - -\stopsection - -\startsection[title={The problem}] - -\METAPOST\ is meant for drawing graphics and adding text to them is not really -part of the concept. Its a bit like how \TEX\ sees images: the dimensions matter, -the content doesn't. This means that in \METAPOST\ a blob of text is an -abstraction. The native way to create a typeset text picture is: - -\starttyping -picture p ; p := btex some text etex ; -\stoptyping - -In traditional \METAPOST\ this will create a temporary \TEX\ file with the words -\type {some text} wrapped in a box that when typeset is just shipped out. The -result is a \DVI\ file that with an auxiliary program will be transformed into a -\METAPOST\ picture. That picture itself is made from multiple pictures, because -each sequences of characters becomes a picture and kerns become shifts. - -There is also a primitive \type {infont} that takes a text and just converts it -into a low level text object but no typesetting is done there: so no ligatures -and no kerns are found there. In \CONTEXT\ this operator is redefined to do the -right thing. - -In both cases, what ends up in the \POSTSCRIPT\ file is references to fonts and -characters and the original idea is that \DVIPS\ understands what -fonts to embed. Details are communicated via specials (comments) that \DVIPS\ is -supposed to intercept and understand. This all happens in an 8~bit (font) universe. - -When we moved on to \PDF, a converter from \METAPOST's rather predictable and -simple \POSTSCRIPT\ code to \PDF\ was written in \TEX. The graphic operators -became \PDF\ operators and the text was retypeset using the font information and -snippets of strings and injected at the right spot. The only complication was -that a non circular pen actually produced two path of which one has to be -transformed. - -At that moment it already had become clear that a more tight integration in -\CONTEXT\ would happen and not only would that demand a more sophisticated -handling of text, but it would also require more features not present in -\METAPOST, like dealing with \CMYK\ colors, special color spaces, transparency, -images, shading, and more. All this was implemented. In the next sections we will -only discuss texts. - -\stopsection - -\startsection[title={Using the traditional method}] - -The \type {btex} approach was not that flexible because what happens is that -\type {btex} triggers the parser to just grabbing everything upto the \type -{etex} and pass that to an external program. It's special scanner mode and -because because of that using macros for typesetting texts is a pain. So, instead -of using this method in \CONTEXT\ we used \type {textext}. Before a run the -\METAPOST\ file was scanned and for each \type {textext} the argument was copied -to a file. The \type {btex} calls were scanned to and replaced by \type {textext} -calls. - -For each processed snippet the dimensions were stored in order to be loaded at -the start of the \METAPOST\ run. In fact, each text was just a rectangle with -certain dimensions. The \PDF\ converter would use the real snippet (by -typesetting it). - -Of course there had to be some housekeeping in order to make sure that the right -snippets were used, because the order of definition (as picture) can be different -from them being used. This mechanism evolved into reasonable robust text handling -but of course was limited by the fact that the file was scanned for snippets. So, -the string had to be string and not assembled one. This disadvantage was -compensated by the fact that we could communicate relevant bits of the -environment and apply all the usual context trickery in texts in a way that was -consistent with the rest of the document. - -A later implementation could communicate the text via specials which is more -flexible. Although we talk of this method in the past sense it is still used in -\MKII. - -\stopsection - -\startsection[title={Using the library}] - -When the \MPLIB\ library showed up in \LUATEX, the same approach was used but -soon we moved on to a different approach. We already used specials to communicate -extensions to the backend, using special colors and fake objects as signals. But -at that time paths got pre- and postscripts fields and those could be used to -really carry information with objects because unlike specials, they were bound to -that object. So, all extensions using specials as well as texts were rewritten to -use these scripts. - -The \type {textext} macro changed its behaviour a bit too. Remember that a -text effectively was just a rectangle with some transformation applied. However -this time the postscript field carried the text and the prescript field some -specifics, like the fact that that we are dealing with text. Using the script made -it possible to carry some more inforation around, like special color demands. - -\starttyping -draw textext("foo") ; -\stoptyping - -Among the prescripts are \typ {tx_index=trial} and \typ {tx_state=trial} -(multiple prescripts are prepended) and the postscript is \type {foo}. In a -second run the prescript is \type {tx_index=trial} and \typ {tx_state=final}. -After the first run we analyze all objects, collect the texts (those with a \type -{tx_} variables set) and typeset them. As part of the second run we pass the -dimensions of each indexed text snippet. Internally before the first run we -\quote {reset} states, then after the first run we \quote {analyze}, and after -the second run we \quote {process} as part of the conversion of output to \PDF. - -\stopsection - -\startsection[title={Using \type {runscript}}] - -When the \type {runscript} feature was introduced in the library we no longer -needed to pass the dimensions via subscripted variables. Instead we could just -run a \LUA\ snippets and ask for the dimensions of a text with some index. This -is conceptually not much different but it saves us creating \METAPOST\ code that -stored the dimensions, at the cost of potentially a bit more runtime due to the -\type {runscript} calls. But the code definitely looks a bit cleaner this way. Of -course we had to keep the dimensions at the \LUA\ end but we already did that -because we stored the preprocessed snippets for final usage. - -\stopsection - -\startsection[title={Using a sub \TEX\ run}] - -We now come the current (post \LUATEX\ 1.08) solution. For reasons I will -mention later a two pass approach is not optimal, but we can live with that, -especially because \CONTEXT\ with \METAFUN\ (which is what we're talking about -here) is quit efficient. More important is that it's kind of ugly to do all the -not that special work twice. In addition to text we also have outlines, graphics -and more mechanisms that needed two passes and all these became one pass -features. - -A \TEX\ run is special in many ways. At some point after starting up \TEX\ -enters the main loop and begins reading text and expanding macros. Normally you -start with a file but soon a macro is seen, and a next level of input is entered, -because as part of the expansion more text can be met, files can be opened, -other macros be expanded. When a macro expands a token register, another level is -entered and the same happens when a \LUA\ call is triggered. Such a call can -print back something to \TEX\ and that has to be scanned as if it came from a -file. - -When token lists (and macros) get expanded, some commands result in direct -actions, others result in expansion only and processing later as one of more -tokens can end up in the input stack. The internals of the engine operate in -miraculous ways. All commands trigger a function call, but some have their own -while others share one with a switch statement (in \CCODE\ speak) because they -belong to a category of similar actions. Some are expanded directly, some get -delayed. - -Does it sound complicated? Well, it is. It's even more so when you consider that -\TEX\ uses nesting, which means pushing and popping local assignments, knows -modes, like horizontal, vertical and math mode, keeps track of interrupts and at -the same type triggers typesetting, par building, page construction and flushing -to the output file. - -It is for this reason plus the fact that users can and will do a lot to influence -that behaviour that there is just one main loop and in many aspects global state. -There are some exceptions, for instance when the output routine is called, which -creates a sort of closure: it interrupts the process and for that reason gets -grouping enforced so that it doesn't influence the main run. But even then the -main loop does the job. - -Starting with version 1.10 \LUATEX\ provides a way to do a local run. There are -two ways provided: expanding a token register and calling a \LUA\ function. It -took a bit of experimenting to reach an implementation that works out reasonable -and many variants were tried. In the appendix we give an example of usage. - -The current variant is reasonable robust and does the job but care is needed. -First of all, as soon as you start piping something to \TEX\ that gets typeset -you'd better in a valid mode. If not, then for instance glyphs can end up in a -vertical list and \LUATEX\ will abort. In case you wonder why we don't intercept -this: we can't because we don't know the users intentions. We cannot enforce a -mode for instance as this can have side effects, think of expanding \type -{\everypar} or injecting an indentation box. Also, as soon as you start juggling -nodes there is no way that \TEX\ can foresee what needs to be copied to -discarded. Normally it works out okay but because in \LUATEX\ you can cheat in -numerous ways with \LUA, you can get into trouble. - -So, what has this to do with \METAPOST ? Well, first of all we could now use a -one pass approach. The \type {textext} macro calls \LUA, which then let \TEX\ do -some typesetting, and then gives back the dimensions to \METAPOST. The \quote -{analyze} phase is now integrated in the run. For a regular text this works quite -well because we just box some text and that's it. However, in the next section we -will see where things get complicated. - -Let's summarize the one pass approach: the \type {textext} macro creates -rectangle with the right dimensions and for doing passes the string to \LUA\ -using \type {runscript}. We store the argument of \type {textext} in a variable, -then call \type {runtoks}, which expands the given token list, where we typeset a -box with the stored text (that we fetch with a \LUA\ call), and the \type -{runscript} passes back the three dimensions as fake \RGB\ color to \METAPOST\ -which applies a \type {scantokens} to the result. So, in principle there is no -real conceptual difference except that we now analyze in|-|place instead of -between runs. I will not show the code here because in \CONTEXT\ we use a wrapper -around \type {runscript} so low level examples won't run well. - -\stopsection - -\startsection[title={Some aspects}] - -An important aspect of the text handling is that the whole text can be -transformed. Normally this is only some scaling but rotation is also quite valid. -In the first approach, the original \METAPOST\ one, we have pictures constructed -of snippets and pictures transform well as long as the backend is not too -confused, something that can happen when for instance very small or large font -scales are used. There were some limitations with respect to the number of fonts -and efficient inclusion when for instance randomization was used (I remember -cases with thousands of font instances). The \PDF\ backend could handle most -cases well, by just using one size and scaling at the \PDF\ level. All the \type -{textext} approaches use rectangles as stubs which is very efficient and permits -all transforms. - -How about color? Think of this situation: - -\starttyping -\startMPcode - draw textext("some \color[red]{text}") - withcolor green ; -\stopMPcode -\stoptyping - -And what about the document color? We suffice by saying that this is all well -supported. Of course using transparency, spot colors etc.\ also needs extensions. -These are however not directly related to texts although we need to take it into -account when dealing with the inclusion. - -\starttyping -\startMPcode - draw textext("some \color[red]{text}") - withcolor "blue" - withtransparency (1,0.5) ; -\stopMPcode -\stoptyping - -What if you have a graphic with many small snippets of which many have the same -content? These are by default shared, but if needed you can disable it. This makes -sense if you have a case like this: - -\starttyping -\useMPlibrary[dum] - -\startMPcode - draw textext("\externalfigure[unknown]") notcached ; - draw textext("\externalfigure[unknown]") notcached ; -\stopMPcode -\stoptyping - -Normally each unknown image gets a nice placeholder with some random properties. -So, do we want these two to have the same or not? At least you can control it. - -When I said that things can get complicated with the one pass approach the -previous code snippet is a good example. The dummy figure is generated by -\METAPOST. So, as we have one pass, and jump temporarily back to \TEX, -we have two problems: we reenter the \MPLIB\ instance again in the middle of -a run, and we might pipe back something to and|/|or from \TEX\ nested. - -The first problem could be solved by starting a new \MPLIB\ session. This -normally is not a problem as both runs are independent of each other. In -\CONTEXT\ we can have \METAPOST\ runs in many places and some produce some more -of less stand alone graphic in the text while other calls produce \PDF\ code in -the backend that is used in a different way (for instance in a font). In the -first case the result gets nicely wrapped in a box, while in the second case it -might directly end up in the page stream. And, as \TEX\ has no knowledge of what -is needed, it's here that we can get the complications that can lead to aborting -a run when you are careless. But in any case, if you abort, then you can be sure -you're doing the wrong thing. So, the second problem can only be solved by -careful programming. - -When I ran the test suite on the new code, some older modules had to be fixed. -They were doing the right thing from the perspective of intermediate runs and -therefore independent box handling, putting a text in a box and collecting -dimensions, but interwoven they demanded a bit more defensive programming. For -instance, the multi|-|pass approach always made copies snippets while the one -pass approach does that only when needed. And that confused some old code in a -module, which incidentally is never used today because we have better -functionality built|-|in (the \METAFUN\ \type {followtext} mechanism). - -The two pass approach has special code for cases where a text is not used. -Imagine this: - -\starttyping -picture p ; p := textext("foo") ; - -draw boundingbox p; -\stoptyping - -Here the \quote {analyze} stage will never see the text because we don't flush p. -However because \type {textext} is called it can also make sure we still know the -dimensions. In the next case we do use the text but in two different ways. These -subtle aspects are dealt with properly and could be made a it simpler in the -single pass approach. - -\starttyping -picture p ; p := textext("foo") ; - -draw p rotated 90 withcolor red ; -draw p withcolor green ; -\stoptyping - -\stopsection - -\startsection[title=One or two runs] - -So are we better off now? One problem with two passes is that if you use the -equation solver you need to make sure that you don't run into the redundant -equation issue. So, you need to manage your variables well. In fact you need to -do that anyway because you can call out to \METAPOST\ many times in a run so old -variables can interfere anyway. So yes, we're better off here. - -Are we worse off now? The two runs with in between the text processing is very -robust. There is no interference of nested runs and no interference of nested -local \TEX\ calls. So, maybe we're also bit worse off. You need to anyhow keep -this in mind when you write your own low level \TEX|-|\METAPOST\ interaction -trickery, but fortunately now many users do that. And if you did write your own -plugins, you now need to make them single pass. - -The new code is conceptually cleaner but also still not trivial because due to -the mentioned complications. It's definitely less code but somehow amputating the -old code does hurt a bit. Maybe I should keep it around as reference of how text -handling evolved over a few decades. - -\stopsection - -\startsection[title=Appendix] - -Because the single pass approach made me finally look into a (although somewhat -limited) local \TEX\ run, I will show a simple example. For the sake of -generality I will use \type {\directlua}. Say that you need the dimensions of a -box while in \LUA: - -\startbuffer -\directlua { - tex.sprint("result 1: <") - - tex.sprint("\\setbox0\\hbox{one}") - tex.sprint("\\number\\wd0") - - tex.sprint("\\setbox0\\hbox{\\directlua{tex.print{'first'}}}") - tex.sprint(",") - tex.sprint("\\number\\wd0") - - tex.sprint(">") -} -\stopbuffer - -\typebuffer \getbuffer - -This looks ok, but only because all printed text is collected and pushed into a -new input level once the \LUA\ call is done. So take this then: - -\startbuffer -\directlua { - tex.sprint("result 2: <") - - tex.sprint("\\setbox0\\hbox{one}") - tex.sprint(tex.getbox(0).width) - - tex.sprint("\\setbox0\\hbox{\\directlua{tex.print{'first'}}}") - tex.sprint(",") - tex.sprint(tex.getbox(0).width) - - tex.sprint(">") -} -\stopbuffer - -\typebuffer \getbuffer - -This time we get the widths of the box known at the moment that we are in \LUA, -but we haven't typeset the content yet, so we get the wrong dimensions. This -however will work okay: - -\startbuffer -\toks0{\setbox0\hbox{one}} -\toks2{\setbox0\hbox{first}} -\directlua { - tex.forcehmode(true) - - tex.sprint("<") - - tex.runtoks(0) - tex.sprint(tex.getbox(0).width) - - tex.runtoks(2) - tex.sprint(",") - tex.sprint(tex.getbox(0).width) - - tex.sprint(">") -} -\stopbuffer - -\typebuffer \getbuffer - -as does this: - -\startbuffer -\toks0{\setbox0\hbox{\directlua{tex.sprint(MyGlobalText)}}} -\directlua { - tex.forcehmode(true) - - tex.sprint("result 3: <") - - MyGlobalText = "one" - tex.runtoks(0) - tex.sprint(tex.getbox(0).width) - - MyGlobalText = "first" - tex.runtoks(0) - tex.sprint(",") - tex.sprint(tex.getbox(0).width) - - tex.sprint(">") -} -\stopbuffer - -\typebuffer \getbuffer - -Here is a variant that uses functions: - -\startbuffer -\directlua { - tex.forcehmode(true) - - tex.sprint("result 4: <") - - tex.runtoks(function() - tex.sprint("\\setbox0\\hbox{one}") - end) - tex.sprint(tex.getbox(0).width) - - tex.runtoks(function() - tex.sprint("\\setbox0\\hbox{\\directlua{tex.print{'first'}}}") - end) - tex.sprint(",") - tex.sprint(tex.getbox(0).width) - - tex.sprint(">") -} -\stopbuffer - -\typebuffer \getbuffer - -The \type {forcemode} is needed when you do this in vertical mode. Otherwise the -run aborts. Of course you can also force horizontal mode before the call. I'm -sure that users will be surprised by side effects when they really use this -feature but that is to be expected: you really need to be aware of the subtle -interference of input levels and mix of input media (files, token lists, macros -or \LUA) as well as the fact that \TEX\ often looks one token ahead, and often, -when forced to typeset something, also can trigger builders. You're warned. - -\stopsection - -\stopchapter - -\stopcomponent - -% \starttext - -% \toks0{\hbox{test}} [\ctxlua{tex.runtoks(0)}]\par - -% \toks0{\relax\relax\hbox{test}\relax\relax}[\ctxlua{tex.runtoks(0)}]\par - -% \toks0{xxxxxxx} [\ctxlua{tex.runtoks(0)}]\par - -% \toks0{\hbox{(\ctxlua{context("test")})}} [\ctxlua{tex.runtoks(0)}]\par - -% \toks0{\global\setbox1\hbox{(\ctxlua{context("test")})}} [\ctxlua{tex.runtoks(0)}\box1]\par - -% \startluacode -% local s = "[\\ctxlua{tex.runtoks(0)}\\box1]" -% context("<") -% context( function() context(s) end) -% context( function() context(s) end) -% context(">") -% \stopluacode\par - -% \toks10000{\hbox{\red test1}} -% \toks10002{\green\hbox{test2}} -% \toks10004{\hbox{\global\setbox1\hbox to 1000sp{\directlua{context("!4!")}}}} -% \toks10006{\hbox{\global\setbox3\hbox to 2000sp{\directlua{context("?6?")}}}} -% \hbox{x\startluacode -% local s0 = "(\\hbox{\\ctxlua{tex.runtoks(10000)}})" -% local s2 = "[\\hbox{\\ctxlua{tex.runtoks(10002)}}]" -% context("<!") -% -- context( function() context(s0) end) -% -- context( function() context(s0) end) -% -- context( function() context(s2) end) -% context(s0) -% context(s0) -% context(s2) -% context("<") -% tex.runtoks(10004) -% context("X") -% tex.runtoks(10006) -% context(tex.box[1].width) -% context("/") -% context(tex.box[3].width) -% context("!>") -% \stopluacode x}\par - - |