Tikz 循环上的箭头不显示

Question

我正在尝试绘制一个带有方框之间箭头的图表。大多数箭头都显示正常，但从节点到其自身的循环上的箭头却显示不正常。

由于默认箭头太小，因此我定义了自定义箭头。

\documentclass{article}

\usepackage{tikz}
\usetikzlibrary{arrows}
\usetikzlibrary{decorations.markings}

\tikzset{
    myarrow/.style={
        decoration={markings,mark=at position 1 with {\arrow[scale=2]{>}}},
        postaction={decorate},
        >=stealth
    }
}

\begin{document}
\begin{tikzpicture}
    \node [rectangle, fill=none, draw=black, text centered, inner sep=1em] 
        (box) 
        at (0, 0) 
        {box};
    \node [rectangle, fill=none, draw=black, text centered, inner sep=1em] 
        (second box) 
        at (3, 0) 
        {second box};

    % this works
    \draw [myarrow] (box.east) -- (second box.west);

    % but this doesn't
    \draw (box.north west)
        edge[myarrow, out = 120, in = 60, min distance = 3em]
        node [anchor = south] {feedback}
        (box.north);
\end{tikzpicture}
\end{document}

圆环上的箭头没有出现，而直线上的箭头却出现了。这是为什么呢？带有圆环的盒子应该看起来像这样（糟糕的 Photoshop）：

使用默认的（微小）箭头有效：

定义myarrow错误吗？

非常感谢您的帮助。

Answer 1

这可能是舍入错误。如果我使用at position 0.999箭头显示。

然而，将其用于直箭可能不是最佳选择，因此我还定义了一种myarrowstraight样式以便进行比较。

\documentclass{article}

\usepackage{tikz}
\usetikzlibrary{arrows}
\usetikzlibrary{decorations.markings}

\tikzset{
    myarrow/.style={
        decoration={markings,mark=at position 0.999 with {\arrow[scale=2]{>}}},
        postaction={decorate},
        >=stealth
    },
    myarrowstraight/.style={
        decoration={markings,mark=at position 1 with {\arrow[scale=2]{>}}},
        postaction={decorate},
        >=stealth
    },
}

\begin{document}
\begin{tikzpicture}
    \node [rectangle, fill=none, draw=black, text centered, inner sep=1em] 
        (box) 
        at (0, 0) 
        {box};
    \node [rectangle, fill=none, draw=black, text centered, inner sep=1em] 
        (second box) 
        at (3, 0) 
        {second box};

    % this works
    \draw [myarrow] (box.east) -- (second box.west);

    \draw [myarrowstraight] (box.north east) -- (second box.north west);

    % but this doesn't
    \draw (box.north west)
        edge[myarrow, out = 120, in = 60, min distance = 3em]
        node [anchor = south] {feedback}
        (box.north);
\end{tikzpicture}
\end{document}

箭头使用该north east样式，可能会注意到箭头的微小偏移。north westmyarrowstraight