Re: MetaFun: Confusion with `function()` and `xyscaled`

[Paul Menzel <paulepanter@users.sourceforge.net>]

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Am Freitag, den 21.10.2011, 01:14 +0200 schrieb Paul Menzel:
> Dear ConTeXt/MetaFun folks,
> 
> 
> looking at the example for grid and functions in the MetaFun manual [1]
> section 9.3
> 
>         drawoptions(withpen pencircle scaled .25pt withcolor .5white) ;
>         draw hlingrid(0, 20, .2, 20cm, 10cm) ;
>         draw vloggrid(0, 10, .5, 10cm, 20cm) ;
>         drawoptions(withpen pencircle scaled .50pt) ;
>         draw hlingrid(0, 20, 1, 20cm, 10cm) ;
>         draw vloggrid(0, 10, 1, 10cm, 20cm) ;
>         
>         fmt_pictures := false ; % use TeX as formatting engine
>         textextoffset := ExHeight ; % a variable set by ConTeXt
>         draw hlintext.lft(0, 20, 5, 20cm, "@3e") ;
>         draw vlogtext.bot(0, 10, 9, 10cm, "@3e") ;
>         
>         draw
>         function(1,"log(x)","x",1,10,1) xyscaled (10cm,2cm)
>         withpen pencircle scaled 5mm withcolor transparent(1,.5,yellow) ;
> 
> I am confused how the resulting function is scaled correctly. The
> resulting dimensions seem to be 10cm and 18 cm. So I guess the 2 cm mean
> to shift it up some how.
> 
> Could someone please explain to me how `xyscaled` works in this case
> please. I though `xyscaled (αcm, ζcm)` would set the object/path to a
> width of α cm and a height of ζ cm.

Looking up the definition of the macro `xyscaled` it is indeed just a
short version of `xscaled αcm yscaled ζcm`.

        $ more mp-tool.mp
        […]
        %D More robust:
        
        % let  normalscaled =  scaled ;
        % let normalxscaled = xscaled ;
        % let normalyscaled = yscaled ;
        %
        % def  scaled expr s =  normalscaled (s) enddef ;
        % def xscaled expr s = normalxscaled (s) enddef ;
        % def yscaled expr s = normalyscaled (s) enddef ;
        
        %D Shorter
        
        primarydef p xyscaled q =
          begingroup ; save qq ; pair qq ; qq = paired(q) ;
            ( p
              if xpart qq<>0 : xscaled (xpart qq) fi
              if ypart qq<>0 : yscaled (ypart qq) fi )
          endgroup
        enddef ;
        […]

I am still confused though what happens in the above example scaling the
path of the function.

Trying

        \starttext
        \startMPcode
          draw fullsquare xscaled 10cm yscaled 2cm;
        \stopMPcode
        \stoptext

the resulting rectangle has the dimensions of 10 cm width and 2 cm
height but the path of the function above does not.


Thanks,

Paul


> [1] http://www.pragma-ade.com/general/manuals/metafun-s.pdf

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