Multi-color circular gradient in Tikz

gradienttikz-pgf

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?

Best Answer

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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