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短路径中不完整的路径衰落“梯度范围”

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短路径中不完整的路径衰落“梯度范围”

我想画一条（非常粗的）线，一端逐渐褪色。我的想法是画一条线，将其延伸，然后path fading仅应用于延伸的部分。对于较短的延伸，褪色似乎不完整（参见 MWE 中的红色和蓝色框）。对于较长的延伸，似乎覆盖了整个渐变范围。

有没有办法可以覆盖短路径的完整梯度范围？

\documentclass{standalone}

\usepackage{tikz}
\usetikzlibrary{fadings}

\begin{document}

    \begin{tikzpicture}[ultra thick, black]

            \draw (0,0) coordinate (ori) -- ++(1cm,0) coordinate (GradStart);
            \draw[path fading=east] (GradStart) -- ++(0.3cm,0) coordinate (GradEnd);
            \draw[red,very thin] (GradStart) ++(-0.1cm,-0.1cm) rectangle ++(0.2cm,0.2cm);
            \draw[blue,very thin] (GradEnd) ++(-0.1cm,-0.1cm) rectangle ++(0.2cm,0.2cm);

            \foreach \length in {0.5,1,3,5}{                
                \draw (ori) ++(0,-0.33) coordinate (ori) -- ++(1cm,0) coordinate (GradStart);
                \draw[path fading=east] (GradStart) -- ++(\length,0) coordinate (GradEnd);
                \draw[red,very thin] (GradStart) ++(-0.1cm,-0.1cm) rectangle ++(0.2cm,0.2cm);
                \draw[blue,very thin] (GradEnd) ++(-0.1cm,-0.1cm) rectangle ++(0.2cm,0.2cm);
            }

    \end{tikzpicture}

\end{document}

在此处输入图片描述

答案1

比较前两行（一行带有line cap=butt，另一行带有line cap=rect）。两个边界框相同（边界框是 所用的区域path fading）。

使用line cap=rect和shorten >不是shorten <一个解决方案（第三行）。

一种可能的解决方案是使用明确的简化（第四行 = 绿色）。

在此处输入图片描述

\documentclass[tikz]{standalone}
\usetikzlibrary{fadings}
\begin{document}
\begin{tikzpicture}
  \draw[orange,line width=.1pt] (0,0) -- (2mm,0);

  \draw[red,line width=1mm,path fading=east,line cap=butt] (0,0) -- (2mm,0);
  \draw[red,line width=1mm,path fading=east,line cap=rect] (0,1mm) -- (2mm,1mm);

  \draw[red,line width=1mm,path fading=east,line cap=rect,shorten <=.5mm,shorten >=.5mm]
  (0,2mm) -- (2mm,2mm);

  \draw[green,path fading=east,line width=1mm,line cap=rect]
  (0+.5\pgflinewidth,3mm) -- (2mm-.5\pgflinewidth,3mm);
\end{tikzpicture}
\end{document}

答案2

根据 John Kormylo 的提示，我更改了代码，将线条变成了矩形：

\documentclass{standalone}

\usepackage{tikz}
\usetikzlibrary{fadings}

\begin{document}

    \begin{tikzpicture}[ultra thick, black]

            \fill[black] (0,0) coordinate (ori) ++(0,-0.5\pgflinewidth) rectangle ++(1cm,\pgflinewidth) ++(0,-0.5\pgflinewidth) coordinate (GradStart);
            \fill[black,path fading=east] (GradStart) ++(0,-0.5\pgflinewidth) rectangle ++(0.3cm,\pgflinewidth) ++(0,-0.5\pgflinewidth) coordinate (GradEnd);
            \draw[red,very thin] (GradStart) ++(-0.1cm,-0.1cm) rectangle ++(0.2cm,0.2cm);
            \draw[blue,very thin] (GradEnd) ++(-0.1cm,-0.1cm) rectangle ++(0.2cm,0.2cm);

            \foreach \length in {0.5,1,3,5}{                
                \fill[black] (ori) ++(0,-0.33) coordinate (ori) ++(0,-0.5\pgflinewidth) rectangle ++(1cm,\pgflinewidth) ++(0,-0.5\pgflinewidth) coordinate (GradStart);
                \fill[black,path fading=east] (GradStart) ++(0,-0.5\pgflinewidth) rectangle ++(\length,\pgflinewidth) ++(0,-0.5\pgflinewidth) coordinate (GradEnd);
                \draw[red,very thin] (GradStart) ++(-0.1cm,-0.1cm) rectangle ++(0.2cm,0.2cm);
                \draw[blue,very thin] (GradEnd) ++(-0.1cm,-0.1cm) rectangle ++(0.2cm,0.2cm);
            }

    \end{tikzpicture}

\end{document}

使用此代码，path fading确实也适用于短“行”：

在此处输入图片描述

显然，使用线条会更直接。因此，我仍然想知道为什么path fading短线无法正常工作以及是否可以使其正常工作。

有任何想法吗？

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