<p>坐标表示矩形的对角,该矩形将包围定义圆弧的椭圆。换言之,弧只出现在由该矩形限定的区域内。在</p>
<p>从官方的tcl/tk文档(tkinter构建的技术)(参见<a href="http://tcl.tk/man/tcl8.5/TkCmd/canvas.htm#M111" rel="nofollow">http://tcl.tk/man/tcl8.5/TkCmd/canvas.htm#M111</a>):</p>
<blockquote>
<p>Items of type arc appear on the display as arc-shaped regions. An arc
is a section of an oval delimited by two angles (specified by the
-start and -extent options) and displayed in one of several ways
(specified by the -style option).</p>
<p>Arcs are created with widget commands of the following form:</p>
</blockquote>
<pre><code>pathName create arc x1 y1 x2 y2 ?option value option value ...?
pathName create arc coordList ?option value option value ...?
</code></pre>
<blockquote>
<p>The arguments x1, y1, x2, and y2 or coordList give the coordinates of
two diagonally opposite corners of a rectangular region enclosing the
oval that defines the arc. After the coordinates there may be any
number of option-value pairs, each of which sets one of the
configuration options for the item. These same option-value pairs may
be used in itemconfigure widget commands to change the item's
configuration. An arc item becomes the current item when the mouse
pointer is over any part that is painted or (when fully transparent)
that would be painted if both the -fill and -outline options were
non-empty.</p>
</blockquote>