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diff --git a/doc/context/sources/general/manuals/texit/texit-leaders.tex b/doc/context/sources/general/manuals/texit/texit-leaders.tex new file mode 100644 index 000000000..ed224da5c --- /dev/null +++ b/doc/context/sources/general/manuals/texit/texit-leaders.tex @@ -0,0 +1,247 @@ +\environment texit-style + +\startcomponent texit-leaders + +\startchapter[title={Leaders}] + +The following example comes from a question on the \CONTEXT\ list. It +exhibits a few low level tricks. For the purpose of this example we +use \type {\ruledhbox} instead of \type {\hbox}. We start with a simple +command that puts something at the end of a line: + +\startbuffer +\starttexdefinition MyFill #1 + \removeunwantedspaces + \hfill + \ruledhbox{#1} +\stoptexdefinition +\stopbuffer + +\typebuffer[option=TEX] \getbuffer + +We use this in: + +\startbuffer[sample] +\startitemize[packed,joinedup][rightmargin=3em] + \startitem + \samplefile{ward}\MyFill{DW} + \stopitem +\stopitemize +\stopbuffer + +\typebuffer[sample][option=TEX] + +and get: + +\getbuffer[sample] + +But, the requirement was that we move the number towards the right margin, so +instead we need something: + +\startbuffer +\starttexdefinition MyFill #1 + \removeunwantedspaces + \hfill + \rlap{\ruledhbox to \rightskip{\hss#1}} +\stoptexdefinition +\stopbuffer + +\typebuffer[option=TEX] \getbuffer + +This already looks more like it: + +\getbuffer[sample] + +But also part of the requirements was that there should be dots between the end +of the last sentence and the number. In low level \TEX\ speak that means using +leaders: repeated boxed content where the repitition is driven by a glue +specification. Let's naively use leaders now: + +\startbuffer +\starttexdefinition MyFill #1 + \leaders + \ruledhbox to 1em{\hss.\hss} + \hfill + \ruledhbox{#1} +\stoptexdefinition +\stopbuffer + +\typebuffer[option=TEX] \getbuffer + +Let's see what we get: + +\getbuffer[sample] + +Again we need to move the number to the right. This time we need a different +solution because we need to fill the space in between. When \TEX\ ends a +paragraph it adds \type {\parfillskip} so we will now manipulate that parameter. + +\startbuffer +\starttexdefinition MyFill #1 + \parfillskip-1\rightskip plus 1fil\relax + \leaders + \ruledhbox to 1em{\hss.\hss} + \hfill + \ruledhbox{#1} +\stoptexdefinition +\stopbuffer + +\typebuffer[option=TEX] \getbuffer + +Does it look better? + +\getbuffer[sample] + +Indeed it does, but watch this: + +\startbuffer[sample] +\startitemize[packed,joinedup][rightmargin=8.5em] + \startitem + \samplefile{ward}\MyFill{DW}\par + \samplefile{ward}\par + \samplefile{ward}\MyFill{DW} + \stopitem +\stopitemize +\stopbuffer + +\typebuffer[sample][option=TEX] + +The first \type {\MyFill} will set the \type {\parfillskip} to a value that will +also be used later on. + +\getbuffer[sample] + +The way out is the following + +\startbuffer +\starttexdefinition MyFill #1 + \begingroup + \parfillskip-1\rightskip plus 1fil\relax + \leaders + \ruledhbox to 1em{\hss.\hss} + \hfill + \ruledhbox{#1} + \par + \endgroup +\stoptexdefinition +\stopbuffer + +\typebuffer[option=TEX] \getbuffer + +This looks more or less okay. The \type {\par} keeps the adaption local but for +it to work well, the \type {\par} must be inside the group. + +\getbuffer[sample] + +Now it's time to go for perfection! First of all, we get rid of any leading +spacing. If we need some we should inject it after a cleanup. We also use a +different leader command. Instead of \type {to} we use a \type {spread} so that +we get half the emwidth and not something slightly less due to the width of the +period. + +\startbuffer +\starttexdefinition MyFill #1 + \removeunwantedspaces + \begingroup + \parfillskip-1\rightskip plus 1fil\relax + \cleaders + \ruledhbox spread 1em{\hss.\hss} + \hfill + \ruledhbox{#1} + \par + \endgroup +\stoptexdefinition +\stopbuffer + +\typebuffer[option=TEX] \getbuffer + +So, we end up here: + +\startbuffer[sample] +\startitemize[packed,joinedup][rightmargin=5em] + \startitem + \samplefile{sapolsky}\MyFill{RS}\par + \stopitem +\stopitemize +\stopbuffer + +\getbuffer[sample] + +For which we used this: + +\typebuffer[sample][option=TEX] + +Finally we get rid of the tracing: + +\startbuffer +\starttexdefinition unexpanded MyFill #1 + \begingroup + \parfillskip-1\rightskip plus 1fil\relax + \leaders + \hbox to \emwidth{\hss.\hss} + \hfill + \hbox{#1} + \par + \endgroup +\stoptexdefinition +\stopbuffer + +\typebuffer[option=TEX] \getbuffer + +Watch a few more details. It brings us to: + +\getbuffer[sample] + +\page + +\startbuffer +\definefiller + [MyFiller] + [offset=.25\emwidth, + method=middle] + +\starttexdefinition unexpanded MyFill #1 + \begingroup + \parfillskip-1\rightskip plus 1fil\relax + \filler[MyFiller]% + \hbox{#1} + \par + \endgroup +\stoptexdefinition +\stopbuffer + +\typebuffer[option=TEX] \getbuffer + +\getbuffer[sample] + +When writing these examples I realized that it's rather trivial to add this +option to the already existing filler mechanism. The definition of such a filler +looks like this: + +\startbuffer +\definefiller + [MyFiller] + [offset=.25\emwidth, + rightmargindistance=-\rightskip, + method=middle] +\stopbuffer + +\typebuffer[option=TEX] \getbuffer + +\startbuffer[sample] +\startitemize[packed,joinedup][rightmargin=5em] + \startitem + \samplefile{sapolsky}\fillupto[MyFiller]{RS} + \stopitem +\stopitemize +\stopbuffer + +The sample code now becomes: + +\typebuffer[sample][option=TEX] + +Ans as expected renders as: + +\getbuffer[sample] + +\stopcomponent |