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Thanks Fabrice and Hans.

I now see I can simplify some lines of the code:

pp := ((xpart a[i])/cf*cm, (ypart a[i])/cf*cm); now becomes pp:= a[i];

and

pp := pp --- ((xpart a[i+1]/cf)*cm, (ypart a[i+1])/cf*cm); now becomes pp := pp --- a[i +1] ;

However I still have the problem in the calculation of xcoord and ycoord which are used in the creation of path pp:

	for squig = 1 step 1 until 15:

		xcoord := uniformdeviate(1) - 0.5 + (xpart a[i]/cf);

		ycoord := uniformdeviate(1) - 0.5+ (ypart a[i]/cf);

		pp := pp  .. {curl 100}(xcoord*cm, ycoord*cm);

	endfor;

I'm adding a small random amount to the x and ypart of the pair a[i] to produce a path that is like a squiggle (gribouiller in French, according to Google). I have to use cf to convert to the x and yparts to centimeters since they seem to loose the centimeter units on separation. I can't see anyway round this, or am I missing something?

Thanks

Keith McKay

On 26/11/2020 15:19, Fabrice L wrote:

Hi keith,

Le 26 nov. 2020 à 10:09, Keith McKay <mckaymeister@gmail.com> a écrit :

Hi,

I have been using xpart and ypart to extract these values from pairs of points in a path but I wasn't getting the correct result. I was expecting:

pair (2cm, 11cm) to give xpart 2 and ypart 11

However I was getting:

pair (2cm, 11cm) -> xpart 56.6929 and ypart 311.8096

After much head scratching and reading the MetaPost and MetaFun manuals, I realised that the units of xpart or ypart are in Postcript points or Big Points (bp), and 1 bp is 1/72 of an inch, and thus to get the values of xpart or ypart in cm I would have to use a correction factor. I had made the assumption that since the x and ypart in the pair was in cm that the result would be in cm, but I see now that this is not the case. Will I have to continue doing this or is there some magic within MetaFun which takes account of the units in a pair and outputs the result of x and ypart in the same units?

The MWE belows shows what I have been doing.

Thanks

Keith McKay

%%% MWE %%%

\setuppapersize [A5, landscape][A4, portrait]

\usecolors[crayola]

\starttext

\startMPpage

StartPage;

width := PaperWidth ; height := PaperHeight ; unit := cm ;

numeric squig;

pair a[]; a0 = (2cm,11cm); a1 = (4cm,10cm); a2 = (6cm,9cm); a3 = (8cm,8cm);

show xpart a[0], ypart a[0]; %Example of result from x and ypart before applying correction factor (cf) %

cf := 72/2.54; %Converts points/in to points/cm%

path pp;

for i = 0 step 1 until 3:

pp := ((xpart a[i])/cf*cm, (ypart a[i])/cf*cm);

for squig = 1 step 1 until 15:

xcoord := uniformdeviate(1) - 0.5 + (xpart a[i]/cf);

ycoord := uniformdeviate(1) - 0.5+ (ypart a[i]/cf);

pp := pp .. {curl 100}(xcoord*cm, ycoord*cm);

endfor;

pp := pp --- cycle;

if i < 3 :

pp := pp --- ((xpart a[i+1]/cf)*cm, (ypart a[i+1])/cf*cm);

fi;

f :=((1.4 - 0.6) * uniformdeviate(1)) + 0.8; % Factor to lighten/darken colour %

draw pp withpen pencircle xscaled 0.5mm yscaled .1mm rotated 45 withcolor (f[white,\MPcolor{BurntSienna}]);

endfor;

StopPage;

\stopMPpage

\stoptext

%%%%%%%%%%%%%%

MetaPost (MetaFun) is taking care of everything regarding units. As you ave discovered, everything is translated to a unique internal dimension. So you can write:

a := (1cm,2in) ;

with no problem. The « cm » and « in » parts of the expression will become numbers to translate this number on the right unit.

Fabrice.

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