Multi-color circular gradient in Tikz

Question

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

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

What do you mean by a single gradient that "goes through" the same colors? — gernot, Feb 26 '22 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, Feb 26 '22 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, Feb 26 '22 at 14:04
Something like this coolors.co/gradient-maker/ff0000-ff8000-ffff00-00ff00-008000 (but circular), which replaces the colored sections. — Filippo Bistaffa, Feb 26 '22 at 14:20
See the TikZ manual. Seach for "shading". See in particular section 69 "The Shadings Library". — gernot, Feb 26 '22 at 14:26
To be honest these references were not really helpful for what I wanted. Rather, I would point people to the section 114 "Shadings" of the pgfmanual. Specifically, Section 114.2.2 "Radial Shadings" has an example that does exactly what I want, as demonstrated by jessexknight. — Filippo Bistaffa, Feb 27 '22 at 12:42

score 11 · Accepted Answer · answered Feb 26 '22 at 16:17

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

answered Feb 26 '22 at 16:17

jessexknight

2,732

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 Feb 26 '22 at 16:22
Thanks, very interesting! – Filippo Bistaffa Feb 26 '22 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 Feb 26 '22 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 Feb 27 '22 at 00:32
^ 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 Feb 28 '22 at 19:36

Raffaele Santoro · Answer 2 · 2022-02-26T15:48:58.477

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:

Multi-color circular gradient in Tikz

2 Answers2

MWE

Result