如何用tikz填充不规则图形的颜色

方法不太好, 但是能出来结果 ```tex \documentclass{standalone} \usepackage{tikz} \usetikzlibrary{math} \begin{document} \begin{tikzpicture} \draw [<->] (2,0) -| (0,3); \fill [fill = lightgray] [domain = 0:1,smooth] plot (\x, {pow(\x,2)}) -- (1,2) [domain = 1:0, smooth] -- plot (\x, {2*pow(\x,2)}) -- cycle; \fill [fill = gray] [domain = 0:1,smooth] plot (\x, {2*pow(\x,2)}) -- (0.5,2) [domain = 0.5:0, smooth] -- plot (\x, {8*pow(\x,2)}) -- cycle; \end{tikzpicture} \end{document} ```

使用pgfplots宏包的fillbetween库也许是一个办法。 一个来自[https://tex.stackexchange.com/questions/367668/strange-fill-between-behavior](https://tex.stackexchange.com/questions/367668/strange-fill-between-behavior "https://tex.stackexchange.com/questions/367668/strange-fill-between-behavior")的例子如下： ```tex \documentclass{standalone} \usepackage{tikz,pgfplots} \usepgfplotslibrary{fillbetween} \pgfplotsset{compat=1.3} \begin{document} \begin{tikzpicture} \begin{axis}[ xmin=-2,xmax=2, ymin=0,ymax=4, height = 6cm, minor tick num=1, axis lines=center, axis line style=<-> ] \addplot[name path=G,green,domain={-2:2}] {x^2}; \addplot[name path=F,blue,domain={-2:2}] {-x^2+2}; % \addplot[color=blue!50]fill between[of=G and F, split, clip={domain=-1:1}]; \tikzfillbetween [of=F and G,split,every even segment/.style={white!1}] {red!50}; \end{axis} \end{tikzpicture} \end{document} ``` 另一个来自[https://tex.stackexchange.com/questions/7914/fill-between-two-curves-in-pgfplots](https://tex.stackexchange.com/questions/7914/fill-between-two-curves-in-pgfplots "https://tex.stackexchange.com/questions/7914/fill-between-two-curves-in-pgfplots")的例子为： ```tex \documentclass{standalone} \usepackage{pgfplots} \pgfplotsset{compat=1.10} \usepgfplotslibrary{fillbetween} \begin{document} \begin{tikzpicture} \begin{axis} \addplot[name path=A,blue,mark=*,line width=2pt] table { 0 2 0.5 -1 1 3 }; \addplot[name path=B,orange,mark=*,line width=2pt] coordinates {(0,0) (1,1)}; \addplot[gray!40] fill between[of=A and B]; \end{axis} \end{tikzpicture} \end{document} ``` 可以将函数改为需要的函数，希望对解决问题有用。 可在命令行使用`texdoc pgfplots`查看其使用说明。

一则过度定制的例子 ```tex \documentclass{article} \usepackage{tikz} \usetikzlibrary{patterns.meta} % derived from `texdoc tikz`, sec. 62.3 \tikzdeclarepattern{% name=lines, parameters={ \pgfkeysvalueof{/pgf/pattern keys/size}, \pgfkeysvalueof{/pgf/pattern keys/angle}, \pgfkeysvalueof{/pgf/pattern keys/line width}, \pgfkeysvalueof{/pgf/pattern keys/color}, }, bounding box={(-.1pt,-.1pt) and (\pgfkeysvalueof{/pgf/pattern keys/size}+.1pt, \pgfkeysvalueof{/pgf/pattern keys/size}+.1pt)}, tile size={(\pgfkeysvalueof{/pgf/pattern keys/size}, \pgfkeysvalueof{/pgf/pattern keys/size})}, tile transformation={rotate=\pgfkeysvalueof{/pgf/pattern keys/angle}}, defaults={ size/.initial=5pt, angle/.initial=0, line width/.initial=.2pt, color/.initial=gray, }, code={ \draw[line width=\pgfkeysvalueof{/pgf/pattern keys/line width}, color=\pgfkeysvalueof{/pgf/pattern keys/color}] (0,0) -- (\pgfkeysvalueof{/pgf/pattern keys/size}, \pgfkeysvalueof{/pgf/pattern keys/size}); } } \begin{document} \tikzset{ tag label/.style={ above right, font=\small, inner sep=2pt } } % shorthands: sqr - square, R - reversed \begin{tikzpicture}[scale=2, samples=500] \draw[help lines] (0, 0) grid (2, 2); % slanted lines \fill[pattern={lines[angle=160]}] plot[id=squ, domain=0:1] function{x*x} -- (1, 2) -- (0.5, 2) -- plot[id=8squR, domain=.5:0] function{8*x*x} -- cycle; \fill[pattern={lines[angle=180]}] plot[id=2squ, domain=0:1] function{2*x*x} -- (0.5, 2) -- plot[id=8squR, domain=.5:0] function{8*x*x} -- cycle; % plots and labels \draw plot[id=squ, domain=0:1] function{x*x} node[tag label] {$x^2$}; \draw plot[id=2squ, domain=0:1] function{2*x*x} node[tag label] {$2x^2$}; \draw plot[id=8squ, domain=0:.5] function{8*x*x} node[tag label, above] {$8x^2$}; \end{tikzpicture} \end{document} ```  1. 因为用了 `plot function{...}` 的语法，需要使用 `-shell-escape` 选项并安装 gnuplot 绘图程序。调用 gnuplot 旨在减少坐标重复计算、加快编译速度，用 `plot (<x>, <y>)` 的语法也完全可以。 1. 只要是封闭图形就能 `\fill`，需要注意 `--plot` 和 `plot` 的不同，详见 `texdoc tikz`, sec. 22.2。 1. 提供这个回答只是说明「能画」，个人强烈建议用所见即所得的绘图工具作图。