TikZ-PGF – Using Form-Only Patterns with Variable: Possible Bug

pgf-coretikz-pgf

While trying to use a variable pattern in TikZ with varying pattern color, I found that it did not seem to work. Here's a minimal working example:

\documentclass[tikz]{standalone}
\usetikzlibrary{patterns}
%
%
\tikzset{slope/.store in=\slope}
%
\pgfdeclarepatternformonly[\slope]{slant lines}
{\pgfpoint{-.1mm/\slope}{-.1mm}}{\pgfpoint{1.1mm/\slope}{1.1mm}}
{\pgfpoint{1mm/\slope}{1mm}}
{
    \pgfsetlinewidth{0.4pt}
    \pgfpathmoveto{\pgfpoint{-.1mm/\slope}{-.1mm}}
    \pgfpathlineto{\pgfpoint{1.1mm/\slope}{1.1mm}}
    \pgfusepath{stroke}
}
%
%
\newcommand{\theslope}{0.7}
%
\pgfdeclarepatternformonly{diagonal lines}
{\pgfpoint{-.1mm/\theslope}{-.1mm}}{\pgfpoint{1.1mm/\theslope}{1.1mm}}
{\pgfpoint{1mm/\theslope}{1mm}}
{
    \pgfsetlinewidth{0.4pt}
    \pgfpathmoveto{\pgfpoint{-.1mm/\theslope}{-.1mm}}
    \pgfpathlineto{\pgfpoint{1.1mm/\theslope}{1.1mm}}
    \pgfusepath{stroke}
}
%
%
\begin{document}
\begin{tikzpicture}
    \draw[pattern=diagonal lines,pattern color=blue] (0,0) rectangle (5,5);
    \tikzset{every path/.append style={xshift=6cm}}
    \draw[pattern=slant lines,pattern color=blue,slope=0.7] (0,0) rectangle (5,5);
\end{tikzpicture}
\end{document}

The output looks like this:

enter image description here

If I understand the system correctly, both squares should be filled with diagonal blue lines. But for the variable-slope pattern, the pattern color=blue option seems to have been ignored.

Am I doing something wrong, or is this an actual bug? In either case, is there a reasonable way for me to make it right?

Best Answer

From the manual p.162, As such, form-only patterns do not have any colors of their own, but when it is used the current pattern color is used as its color.

The reason for this is because form-only pattern declarations without variables are frozen so TikZ can set a pattern color beforehand and the pattern inherits that stroke color. However patterns with variables are not frozen and reevaluated whenever they are called. So the color should be set each time independently. As Qrrbirlbel's answer, the color should be provided to the pattern at the time of creation.

\documentclass[tikz]{standalone}
\usetikzlibrary{patterns}
\tikzset{
    slope/.code={\edef\slope{#1}},
    slope/.default=0.5,
    slope
}
\makeatletter
\pgfdeclarepatternformonly[\tikz@pattern@color,\slope]{slant lines}
{\pgfpoint{-.1mm/\slope}{-.1mm}}
{\pgfpoint{1.1mm/\slope}{1.1mm}}
{\pgfpoint{1mm/\slope}{1mm}}
{
    \pgfsetlinewidth{0.4pt}
    \pgfpathmoveto{\pgfpoint{-.1mm/\slope}{-.1mm}}
    \pgfpathlineto{\pgfpoint{1.1mm/\slope}{1.1mm}}
    \pgfsetstrokecolor{\tikz@pattern@color}
    \pgfusepath{stroke}
}
\makeatother
\begin{document}
\begin{tikzpicture}
    \fill[pattern=slant lines,pattern color=red] (0,0) rectangle (5,5);
    \fill[pattern color=blue,pattern=slant lines,slope=0.3] (5,0) rectangle (10,5);
\end{tikzpicture}
\end{document}

enter image description here

Related Solutions

tikz-pgf – How to Use Patterns Inside PGF Shapes

I don't see a way to get the stroke colour from PGF itself (\pgfgetsstrokecolor isn't a defined macro) but fortunately TikZ stores the colour in its own memory space and so it is possible to use that to get the colour. There are three such storage places:

\tikz@strokecolor
\tikz@fillcolor
tikz@color
.

The first two are macros, the last two are colours. The draw=colour option sets the first, the fill=colour option sets the second, and the color=colour options sets both of the last two.

So one solution is to set the colour to be . unless \tikz@strokecolor is set, whereupon we use that. One way of doing this is the following:

\documentclass{article}
\usepackage{tikz}

\usetikzlibrary{patterns}

\makeatletter
\pgfdeclareshape{test shape}
{
  \inheritsavedanchors[from=rectangle]
  \inheritanchor[from=rectangle]{center}

  \backgroundpath
  {
    \def\my@color{.}%
    \ifx\tikz@strokecolor\pgfutil@empty
    \else
    \let\my@color\tikz@strokecolor
    \fi
    \pgfsetfillpattern{north east lines}{\my@color}
    \pgfpathrectanglecorners{\pgfpoint{0}{0}}{\pgfpoint{1cm}{1cm}}
    \pgfusepath{fill}
  }
}
\makeatother
\begin{document}
\begin{tikzpicture}
\node[draw=red,test shape] at (0,0) {};
\node[fill=red,test shape] at (2cm,0) {};
\node[color=red,test shape] at (4cm,0) {};
\end{tikzpicture}
\end{document}

which results in:

coloured patterns

If you want a different combination then you need to adjust the choices.

[Tex/LaTex] Tikz: redefinition of patterns

As mentioned in the comments, I would put the pattern definitions in a separate file and import the definitions file. That way the definitions are kept consistent.

However, if you do not want to do that you could use \providepgfdeclarepatternformonly instead of \pgfdeclarepatternformonly using this definition:

\makeatletter
\newcommand{\providepgfdeclarepatternformonly}[4][]{%
    \pgfutil@ifundefined{pgf@pattern@name@#1}{
        \pgfdeclarepatternformonly{#1}{#2}{#3}{#4}
    }{%
        %Pattern already defined, so don't redefine it
    }%
}
\makeatother

Similar to providecommand, if the pattern is already defined the attempt to redefine it is ignored. Here is the test case where using providepgfdeclarepatternformonly compiles, but pgfdeclarepatternformonly gives the error about pattern already being defined.

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{patterns}

\makeatletter
\newcommand{\providepgfdeclarepatternformonly}[5]{%
    \pgfutil@ifundefined{pgf@pattern@name@#1}{%
        \pgfdeclarepatternformonly{#1}{#2}{#3}{#4}{#5}%
    }{%
        %Pattern already defined, so don't redefine it
    }%
}
\makeatother

\begin{document}

\providepgfdeclarepatternformonly{wide lines}{\pgfqpoint{-1pt}{-1pt}}{\pgfqpoint{12pt}{12pt}}{\pgfqpoint{9pt}{9pt}}%
{
  \pgfsetlinewidth{0.4pt}
  \pgfpathmoveto{\pgfqpoint{0pt}{0pt}}
  \pgfpathlineto{\pgfqpoint{9pt}{9pt}}
  \pgfusepath{stroke}
}

\begin{tikzpicture}
\providepgfdeclarepatternformonly{wide lines}{\pgfqpoint{-1pt}{-1pt}}{\pgfqpoint{12pt}{12pt}}{\pgfqpoint{9pt}{9pt}}%
{
  \pgfsetlinewidth{0.4pt}
  \pgfpathmoveto{\pgfqpoint{0pt}{0pt}}
  \pgfpathlineto{\pgfqpoint{9pt}{9pt}}
  \pgfusepath{stroke}
}

\filldraw[pattern=wide lines] (0,0) rectangle (2,2);
\end{tikzpicture}
\end{document}

Best Answer

Related Solutions

tikz-pgf – How to Use Patterns Inside PGF Shapes

[Tex/LaTex] Tikz: redefinition of patterns

Related Question