5

I'm using the following code

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

\begin{document}
    \begin{tikzpicture}
        \coordinate (y) at (0,10);
        \coordinate (x) at (10,0);
        \coordinate (ya) at ($(y) + (0,1.5)$);
        \coordinate (xa) at ($(x) + (1.5,0)$);
        \begin{scope}
            \clip (0,0) rectangle (x |- y);
            \fill[red] (x) circle (10);
            \fill[orange] (x) circle (8);
            \fill[yellow] (x) circle (6);
            \fill[green] (x) circle (4);
            \fill[green!50!black] (x) circle (2);
        \end{scope}
        \draw[->,thick] (0,-1) -- (ya);
        \draw[->,thick] (-1,0) -- (xa);
    \end{tikzpicture}
\end{document}

to generate this plot

enter image description here

How can I replace the colored circular zones with a single gradient that "goes through" the same colors?

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7
  • What do you mean by a single gradient that "goes through" the same colors?
    – gernot
    Commented Feb 26, 2022 at 13:35
  • A gradient that starts from red, then orange, then yellow, then green, then dark green, i.e., the colors of the colored sections.
    – Filippo Bistaffa
    Commented Feb 26, 2022 at 13:53
  • Still not sure I understand. By gradient, do you mean that the colors change continually from dark green to red, with smooth transitions instead of the jumps? But otherwise the same picture?
    – gernot
    Commented Feb 26, 2022 at 14:04
  • Something like this coolors.co/gradient-maker/ff0000-ff8000-ffff00-00ff00-008000 (but circular), which replaces the colored sections.
    – Filippo Bistaffa
    Commented Feb 26, 2022 at 14:20
  • See the TikZ manual. Seach for "shading". See in particular section 69 "The Shadings Library".
    – gernot
    Commented Feb 26, 2022 at 14:26

2 Answers 2

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11

You can define a custom shading using \pgfdeclareradialshading from the shadings tikz library. The units bp stand for "big points", which, as described here, are automatically rescaled to the bounding box of the current path, such that (50bp,50bp) is the centre and (25bp,25bp) and (75bp,75bp) are the corners. That's why the colors span 0bp to 25bp below, and you can see how the shading can be scaled with the second circle.

(I also removed the \coordinates from your code as they were not directly relevant to the solution.)

MWE

\documentclass[margin=5mm]{standalone}
\usepackage{tikz}
\usetikzlibrary{shadings}
\pgfdeclareradialshading{gyr}{\pgfpoint{0bp}{0bp}}{%
  color(0bp)=(green!50!black);
  color(6.25bp)=(green);
  color(12.5bp)=(yellow);
  color(18.75bp)=(orange);
  color(25bp)=(red)
}
\begin{document}
    \begin{tikzpicture}
        \begin{scope}
          \clip (0,0) rectangle (10,10);
          \shade[shading=gyr] (10,0) circle (10);
          \shade[shading=gyr] (0,10) circle (3);
        \end{scope}
      \draw[->,thick] (0,-1) -- (0,11);
      \draw[->,thick] (-1,0) -- (11,0);
    \end{tikzpicture}
\end{document}

Result

result

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5
  • As an aside, depending on your application, you may consider using custom colours that are more perceptually uniform, such as from the viridis colormaps.
    – jessexknight
    Commented Feb 26, 2022 at 16:22
  • Thanks, very interesting!
    – Filippo Bistaffa
    Commented Feb 26, 2022 at 16:50
  • Just out of interest, is it possible to make some of the transitions less "sharp"? The yellow line and the edge between light and dark green is quite noticeable.
    – MaxD
    Commented Feb 26, 2022 at 22:57
  • 2
    This is exactly the issue of "perceptual uniformity"! Try instead \definecolor{viri}{RGB}{68,1,84}\definecolor{virii}{RGB}{59,82,139}\definecolor{viriii}{RGB}{33,145,140}\definecolor{viriv}{RGB}{94,201,98}\definecolor{virv}{RGB}{253,231,37} and color(0bp)=(viri);color(6.25bp)=(virii);color(12.5bp)=(viriii);color(18.75bp)=(viriv);color(25bp)=(virv). (unfortunately, it seems defining colors on the fly doesn't play nice with pgfdeclareradialshading.
    – jessexknight
    Commented Feb 27, 2022 at 0:32
  • ^ update: the "on the fly" mechanism can actually be used in \pgfdeclareradialshading, but it is actually just a broken color mixing model, as all scaling is relative to the inputs, not a predefined maximum.
    – jessexknight
    Commented Feb 28, 2022 at 19:36
1

I follow your code with little changes:

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{calc}
\usepgflibrary {shadings}

\begin{document}
    \begin{tikzpicture}
        \coordinate (y) at (0,10);
        \coordinate (x) at (10,0);
        \coordinate (ya) at ($(y) + (0,1.5)$);
        \coordinate (xa) at ($(x) + (1.5,0)$);
    \begin{scope}
        \clip (0,0) rectangle (8,8);
        \shade[shading=color wheel] (8,0) circle (8);
    \end{scope}
        \draw[->,thick] (0,-1) -- (ya);
        \draw[->,thick] (-1,0) -- (xa);
    \end{tikzpicture}

\end{document}

Output:

enter image description here

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