Re: Why does this example from the MetaFun manual not work?

[Hans Hagen <j.hagen@xs4all.nl>]

On 4/9/2020 11:01 AM, Taco Hoekwater wrote:
> Hi,
> 
> Using multiple (text <x>) arguments in macros doesn’t work, you would
> need to convert all but the last argument into (expr <x>) somehow.
> 
> That means that you probably cannot do a call like the one below at all.
> (I, at least, do not see how you could convert one of those transparent
> colours into an expr <x> argument)
> 
>>
>> SampleText ("Much Of This", transparent(1, .5, red  ) , transparent(1, .5, green  )) ;
> 
> The situation may get even trickier because withtransparency() and
> transparent() both use a  (text <x>) argument internally as well,
> and I am not quite sure why.
> 
> At this point, I think you may need Hans for advice, sorry.
Taco is right (of course). Indeed, one can end up in conflicts (mp has 
no transparency so it's all implemented using trickery). Anyway, using 
'infont' has no real benefits as it maps onto textext, so one can just 
use that one (also because it supports the anchoring suffixes which 
saves you the shift):

\starttext
\startMPpage[instance=doublefun]

draw textext("more recent"        ) withcolor red     withtransparency 
(1, .5) ;
draw textext("functionality"      ) withcolor green   withtransparency 
(1, .5) ;
draw textext("was written"        ) withcolor blue    withtransparency 
(1, .5) ;
draw textext("while listening"    ) withcolor magenta withtransparency 
(1, .5) ;
draw textext("to superb covers by") withcolor cyan    withtransparency 
(1, .5) ;
draw textext("Alyona Yarushina"   ) withcolor yellow  withtransparency 
(1, .5) ;

\stopMPpage
\stoptext

If something like "withcolor ... " is passed to a macro it has to be a 
text argument, not an expression (the transparent macro actually passed 
some abstraction); also, when making vardef's one need to omit the final 
semi colon in order to apply more properties to the 'return value'.

At some point I will update the metafun manual which means: remove old 
methods and exclusively use the new ones (currently the manual also 
discusses mpii while in context mkiv/lmtx we use mpiv macros).

For instance, when using colors one can best use named colors as these 
are consistent with the tex end, so often

   withcolor "red"

is better than

   withcolor red

etc etc etc etc

Hans


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                                           Hans Hagen | PRAGMA ADE
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