Colors and pictures in plain LuaTeX

As Knuths TeX had no support for colors or pictures, we have to make our own macros for that. The following macros are perhaps a bit simple, but that also means being easy to adapt to different needs and situations.

Images can be placed with an \image{<file>} macro. It can be preceeded with \imageheight or \imagewidth to set dimensions. If a dimension is set to 0pt, the natural size of the image is used. This is very similar to how it's done in Opmac/OpTeX.

\newdimen\imagewidth \imagewidth=0pt % 0pt gives natural size of image
\newdimen\imageheight \imageheight=0pt
\newtoks\imagedir \imagedir{} % Must end with /, e.g. mypics/

\def\image#1{%
	\hbox{%
		\saveimageresource 
			\ifdim\imagewidth=0pt \else width\imagewidth\fi 
            \ifdim\imageheight=0pt \else height\imageheight\fi 
            {\the\imagedir#1}%
      	\useimageresource\lastsavedimageresourceindex
	}%
}

% Example: {\imageheight=4cm \image{mypicture.png}}

Colors can be set like this:

% Token for \aftergroup to reset color
\def\colorstackpop{\pdfextension colorstack 0 pop}

% Switch to CMYK color in current group. Expects four values between 0 and 1
\def\setcmykcolor#1{%
   	\pdfextension colorstack 0 push {#1 k #1 K}% 
   	\aftergroup\colorstackpop
}

% Switch to RGB color in current group. Expects three values between 0 and 1
\def\setrgbcolor#1{%
   	\pdfextension colorstack 0 push {#1 rg #1 RG}% 
   	\aftergroup\colorstackpop
}

% Color names
\def\black{\setcmykcolor{0 0 0 1}}
\def\blue{\setcmykcolor{1 1 0 0}}
\def\red{\setrgbcolor{0.8 0 0}}

% Example: {\blue This is blue text}