用颜色渐变填充光谱曲线

Question 1

随着pgf-spectrav2.1 这是一个相当容易的任务。

% used PGFPlots v1.18.1
\documentclass[border=5pt]{standalone}
\usepackage{pgf-spectra}
\usepackage{pgfplots}
    \usepgfplotslibrary{fillbetween}
    \pgfplotsset{compat=1.18}
\begin{document}
\begin{tikzpicture}
        % create a variable to store the `xmax` value, so we don't need to repeat ourselves
        \pgfmathsetmacro{\xmax}{800}
        % create the shade (using the created variable)
        \pgfspectraplotshade[shade end=\xmax]{visiblespectrum}
    \begin{axis}[
        title=Photon Flux,
        xlabel={Wavelength in nm},
        ylabel={Photon Flux in a.u.},
        xmin=300,
        % (use the variable here too)
        xmax=\xmax,
    ]
        \addplot [smooth, name path=spectrum] coordinates {
            (380,0) (400,5) (500,1) (520,3) (525,8) (530,25)
            (535,23) (540,28) (545,34) (550,20) (555,13)
            (560,8) (580,9) (600,18) (620,7) (680,1) (780,0)
        };
        % (because there is no `shade start` key so far the path has to start at x=0)
        \path [name path=axis] (axis cs:0,0)
            -- (axis cs:\pgfkeysvalueof{/pgfplots/xmax},0);
        \addplot+ [thick,shading=visiblespectrum]
            fill between [of=spectrum and axis];
    \end{axis}
\end{tikzpicture}
\end{document}

Answer

随着pgf-spectrav2.1 这是一个相当容易的任务。

% used PGFPlots v1.18.1
\documentclass[border=5pt]{standalone}
\usepackage{pgf-spectra}
\usepackage{pgfplots}
    \usepgfplotslibrary{fillbetween}
    \pgfplotsset{compat=1.18}
\begin{document}
\begin{tikzpicture}
        % create a variable to store the `xmax` value, so we don't need to repeat ourselves
        \pgfmathsetmacro{\xmax}{800}
        % create the shade (using the created variable)
        \pgfspectraplotshade[shade end=\xmax]{visiblespectrum}
    \begin{axis}[
        title=Photon Flux,
        xlabel={Wavelength in nm},
        ylabel={Photon Flux in a.u.},
        xmin=300,
        % (use the variable here too)
        xmax=\xmax,
    ]
        \addplot [smooth, name path=spectrum] coordinates {
            (380,0) (400,5) (500,1) (520,3) (525,8) (530,25)
            (535,23) (540,28) (545,34) (550,20) (555,13)
            (560,8) (580,9) (600,18) (620,7) (680,1) (780,0)
        };
        % (because there is no `shade start` key so far the path has to start at x=0)
        \path [name path=axis] (axis cs:0,0)
            -- (axis cs:\pgfkeysvalueof{/pgfplots/xmax},0);
        \addplot+ [thick,shading=visiblespectrum]
            fill between [of=spectrum and axis];
    \end{axis}
\end{tikzpicture}
\end{document}

Question 2

我自己找到了一个解决方案，尽管它并不完美。

用于填充的阴影似乎经过缩放以适合要填充区域的最左侧和最右侧点之间。因此，\path[name path=axis] (axis cs:0,0) -- (axis cs:1,0);我没有在曲线之间填充，而是将一条线定义\addplot[name path=axis] plot[] coordinates{ (400,0)(800,0) };为路径，其中 x=400 和 x=800 是我想要阴影边界的位置。

这种方法的缺点是，只有当底层（辅助路径/假“轴”）比实际曲线长时，这种方法才有效。在这种情况下，要么需要扩展阴影，要么需要将绘制的数据剪裁到所需范围（可以使用domain或xmin/xmax不使用）。

我的最终文档如下所示：

\documentclass{article}

\usepackage{pgfplots}
\usepgfplotslibrary{fillbetween}

\pgfdeclarehorizontalshading{visiblespectrum}{100bp}{
color(0bp)=(violet);
color(6.25bp)=(blue);
color(12.5bp)=(cyan);
color(18.75bp)=(green);
color(23.75bp)=(yellow);
color(27.5bp)=(orange);
color(31.25bp)=(red);
color(50bp)=(black)
}

\begin{document}

\begin{tikzpicture}
    \begin{axis}[
            width=5cm,
            title= Photon Flux,
            xlabel={Wavelength [nm]},
            ylabel={Photon Flux [a.u.]},
            xmin=400,
            xmax=800
        ]
        \addplot[name path=spectrum] plot[] coordinates{
            ( 400, 5 )
            ( 420, 4 )
            ( 500, 9 )
            ( 520, 13 )
            ( 525, 8 )
            ( 530, 25 )
            ( 535, 23 )
            ( 540, 28 )
            ( 545, 34 )
            ( 550, 20 )
            ( 555, 13 )
            ( 560, 8 )
            ( 580, 9 )
            ( 600, 18 )
            ( 620, 7 )
            ( 680, 5 )
        };
        \addplot[ name path=axis] plot[] coordinates{
            (400,0)
            (800,0)
        };
        \addplot+ [
                thick,
                shading=visiblespectrum, 
                fill opacity=0.5,
        ]
        fill between[
            of=spectrum and axis
        ];
    \end{axis}
\end{tikzpicture}

\end{document}

...给出以下输出：

Answer