Generate random color in way that works with both pdflatex and lualatex

Right now, I am generating a random color in pdftex using

definecolorrandomcolorRGB pdfuniformdeviate 255, pdfuniformdeviate 255, pdfuniformdeviate 255

Which works pretty well,
until I try and compile with luatex.

What is the nicest way to generate random colors (either directly or via generating 3 random numbers), that is compatible across both pdftex and luatex?

I suspect something involving pgf is the answer.
Or maybe just a condition with one branch for pdftex (that looks like the current), and one for luatex (that maybe invokes a tiny snippet of luacode).

Is the luatex85 package usable? It brings back all the deleted pdf... macros to lualatex
– daleif
Aug 21 at 11:06

luatex85

pdf...

lualatex

@daleif yes. Expand that into an answer, with a link to the docs maybe and that would be great. Assuming luatex85 is a no-op or something in pdftex
– Lyndon White
Aug 21 at 11:14

3 Answers
3

The luatex85 package does

luatex85

letpdfuniformdeviateuniformdeviate

You can thus do usepackageluatex85 or

usepackageluatex85

documentclassarticle usepackagexcolor unlessifdefinedpdfuniformdeviate letpdfuniformdeviateuniformdeviate fi definecolorrandomcolorRGB pdfuniformdeviate 255, pdfuniformdeviate 255, pdfuniformdeviate 255 extractcolorspecrandomcolortest typeouttest stop

This will type out something like

rgb0.84706,0.4,0.68234

with both pdflatex or lualatex. I guess that, when random numbers will be available also in xelatex, a common interface will be added to the LaTeX kernel.

pdflatex

lualatex

xelatex

Based on Randomly assign background colour for each frame

Another approach based on pgf:

pgf

documentclassarticle usepackagepgf usepackagepgffor usepackagexcolor usepackageifluatex usepackageifxetex ifluatex letpdfrandomseedrandomseed fi ifxetex pgfmathsetseedtime else pgfmathsetseednumberpdfrandomseed fi newcommandrandomcolor% pgfmathsetmacroRrnd% pgfmathsetmacroGrnd% pgfmathsetmacroBrnd% definecolorrandomcolrgbR,G,B% begindocument noindent% foreach n in 1,...,1350% randomcolorcolorrandomcolrule0.41cm0.41cm-% enddocument

enter image description here

There is also the lcg package (short for Linear Congruential Generator), that works with all compilers, including lualatex. The package provides a command rand to generate a random number and store it in the rand counter. For use in definecolor you should convert the counter with thevalue.

lcg

lualatex

rand

definecolor

thevalue

You can set the bounds of the random generator with the package options first and last, and optionally change them within the document using the reinitrand command. The default seed is based on the system clock, using the minutes as unit (so the output will change only once per minute). You can also provide a custom seed.

first

last

reinitrand

MWE:

documentclassarticle usepackage[first=1,last=255]lcg usepackagexcolor randedefcolorathevaluerand randedefcolorbthevaluerand randedefcolorcthevaluerand definecolorrandomcolorRGB colora, colorb, colorc begindocument colorboxrandomcolorRandom color: colora,colorb,colorc enddocument

Result:

enter image description here

Use thevaluerand instead of arabic. arabic is a formatting command and there is no garanty that it gives a number (e.g. hebrew and arabic packages often redefine it).
– Ulrike Fischer
Aug 21 at 19:08

thevaluerand

arabic

@UlrikeFischer thanks for the improvement, it didn't occur to me to put the there - edited.
– Marijn
Aug 23 at 11:42

the

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