似乎smooth应用于线条的选项有时会影响箭头尖端并产生不正确的结果。垂直线没有问题，但其他任何线似乎都有问题。这是一个已知的错误，还是有理由smooth不应该将其应用于直线？
更新：显示问题不会发生在 TikZ 上，并且如果smooth应用选项，曲线也会发生问题。
\documentclass{article}
\usepackage{pgfplots}
\begin{document}
\tikzstyle{MyStyle} =[->, black, ultra thick, ]
\tikzstyle{MyStyleSmooth}=[->, black, ultra thick, smooth]
\begin{tikzpicture}
\begin{axis}
% 'smooth' option seems to have no effect on lines '1' and '2'
\addplot [MyStyle , green ] coordinates{(0,0) (0,1)} node [above] {1};
\addplot [MyStyleSmooth, blue ] coordinates{(1,0) (1,1)} node [below] {2};
%
% But, can't seem to have the 'smooth' on lines, '4', '5' and '6'
\addplot [MyStyle , orange] coordinates{(2,0) (3,0) } node [right] {3};
\addplot [MyStyleSmooth, red ] coordinates{(4,0) (2,0.5) } node [below] {4};
\addplot [MyStyleSmooth, red ] coordinates{(2,1) (3,1) } node [left ] {5};
\addplot [MyStyleSmooth, red ] coordinates{(3,0.8) (2,0.8) } node [right] {6};
% Similar problem with curves: "non-smooth" is ok, "smooth" is not
\addplot[MyStyle, mark=none, domain=0:1,samples=50, blue] (x,x*x+1);
\addplot[MyStyleSmooth, mark=none, domain=0:1,samples=50, red ] (x,x*x+2);
\end{axis}
\end{tikzpicture}
\begin{tikzpicture} % These are all fine
\draw [MyStyle , green ] (0,0) -- (0,1) node [above] {1};
\draw [MyStyleSmooth, blue ] (1,0) -- (1,1) node [above] {2};
%
\draw [MyStyle , orange] (2,0) -- (3,0) node [right] {3};
\draw [MyStyleSmooth, red ] (4,0) -- (2,0.5) node [below] {4};
\draw [MyStyleSmooth, red ] (2,1) -- (3,1) node [right] {5};
\draw [MyStyleSmooth, red ] (3,0.8) -- (2,0.8) node [left ] {6};
\end{tikzpicture}
\end{document}
答案1
问题不在于 PGFplots，而在于 PGFplot命令（PGFplots 使用该命令绘制图表）：
\tikz\draw [smooth,thick,->] plot coordinates {(0,0) (0.5,0.1) (1,0)};
产量
发生的事情如下：设置smooth命令\draw plot会启动\pgfplothandlercurveto例程（这不是 PGFplots，而是 PGF）pgflibraryplothanders.code.tex。此例程使用命令绘制图中的最后一段
\pgfpathcurveto{\pgf@plot@curveto@first@support}{\pgf@plot@curveto@second}{\pgf@plot@curveto@second}%
这是一个 PGF 曲线命令，它使用两个支撑点将曲线从当前位置延伸到目的地。在这种情况下，第二个支撑点和目的地是同一个点 ( \pgf@plot@curveto@second)，这确保曲线可以从任何方向进入最后一个点。然而，它的缺点是，该段的最后一部分总是会退化（从 A 到 A... 的一条线），这被解释为指向上方。这最后一部分用于定位箭头尖端。
为了防止使用最后一部分，我们可以重新定义有问题的函数来使用\pgfpathcurvebetweentimecontinue，它只绘制最后一行的一部分。将\pgfpathcurveto上面的命令替换为
\pgfpathcurvebetweentimecontinue{0}{0.995}{\pgf@plot@curveto@first}{\pgf@plot@curveto@first@support}{\pgf@plot@curveto@second}{\pgf@plot@curveto@second}%
只绘制了线条的最后 99.5%，这排除了退化部分，但在视觉上是相同的，特别是因为箭头尖端覆盖了线条的末端。我不确定这个值是否适用于所有情况，但它确实适用于您的测试用例：
\documentclass{article}
\usepackage{pgfplots}
\begin{document}
\makeatletter
\def\pgf@plot@curveto@handler@finish{%
\ifpgf@plot@started%
\pgfpathcurvebetweentimecontinue{0}{0.995}{\pgf@plot@curveto@first}{\pgf@plot@curveto@first@support}{\pgf@plot@curveto@second}{\pgf@plot@curveto@second}%
\fi%
}
\makeatother
\tikzstyle{MyStyle} =[->, black, ultra thick, ]
\tikzstyle{MyStyleSmooth}=[->, black, ultra thick, smooth]
\begin{tikzpicture}
\begin{axis}
% 'smooth' option seems to have no effect on lines '1' and '2'
\addplot [MyStyle , green ] coordinates{(0,0) (0,1)} node [above] {1};
\addplot [MyStyleSmooth, blue ] coordinates{(1,0) (1,1)} node [below] {2};
%
% But, can't seem to have the 'smooth' on lines, '4', '5' and '6'
\addplot [MyStyle , orange] coordinates{(2,0) (3,0) } node [right] {3};
\addplot [MyStyleSmooth, red ] coordinates{(4,0) (2,0.5) } node [below] {4};
\addplot [MyStyleSmooth, red ] coordinates{(2,1) (3,1) } node [left ] {5};
\addplot [MyStyleSmooth, red ] coordinates{(3,0.8) (2,0.8) } node [right] {6};
% Similar problem with curves: "non-smooth" is ok, "smooth" is not
\addplot[MyStyle, mark=none, domain=0:1,samples=50, blue] (x,x*x+1);
\addplot[MyStyleSmooth, mark=none, domain=0:1,samples=50, red ] (x,x*x+2);
\end{axis}
\end{tikzpicture}
\begin{tikzpicture} % These are all fine
\draw [MyStyle , green ] (0,0) -- (0,1) node [above] {1};
\draw [MyStyleSmooth, blue ] (1,0) -- (1,1) node [above] {2};
%
\draw [MyStyle , orange] (2,0) -- (3,0) node [right] {3};
\draw [MyStyleSmooth, red ] (4,0) -- (2,0.5) node [below] {4};
\draw [MyStyleSmooth, red ] (2,1) -- (3,1) node [right] {5};
\draw [MyStyleSmooth, red ] (3,0.8) -- (2,0.8) node [left ] {6};
\end{tikzpicture}
\end{document}
