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</span><span style="FONT-FAMILY: 宋体">首先介绍</span><span lang="EN-US"> Point</span><span style="FONT-FAMILY: 宋体">。从概念上讲，</span><span lang="EN-US">Point</span><span style="FONT-FAMILY: 宋体">在这些结构中是最简单的，在数学上，它完全等价于一个二维矢量，包含两个公共整型属性，表示它与某个特定位置的水平和垂直距离</span><span lang="EN-US">(</span><span style="FONT-FAMILY: 宋体">在屏幕上</span><span lang="EN-US">)</span><span style="FONT-FAMILY: 宋体">，如图</span><span lang="EN-US">20-3</span><span style="FONT-FAMILY: 宋体">所示。</span></p>
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                        <p class="MsoNormal"><span lang="EN-US" style="FONT-SIZE: 7.5pt">10</span><span style="FONT-SIZE: 7.5pt; FONT-FAMILY: 宋体">个单位</span></p>
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                        <p class="MsoNormal"><span lang="EN-US" style="FONT-SIZE: 7.5pt">Y</span></p>
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                        <p class="MsoNormal"><span style="FONT-SIZE: 7.5pt; FONT-FAMILY: 宋体">点</span><span lang="EN-US" style="FONT-SIZE: 7.5pt">B</span></p>
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</span><span lang="EN-US"><img height="84" width="224" alt="" src="20/image003.jpg" /></span></p>
<p style="FTEL: 8.15pt" align="center"><span style="FONT-FAMILY: 宋体">图</span><span lang="EN-US">&nbsp; 20-3</span></p>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体">为了从点</span><span lang="EN-US">A</span><span style="FONT-FAMILY: 宋体">到点</span><span lang="EN-US">B</span><span style="FONT-FAMILY: 宋体">，需要水平移动</span><span lang="EN-US">20</span><span style="FONT-FAMILY: 宋体">个单位，并向下垂直移动</span><span lang="EN-US">10</span><span style="FONT-FAMILY: 宋体">个单位，在图中标为</span><span lang="EN-US">x</span><span style="FONT-FAMILY: 宋体">和</span><span lang="EN-US">y</span><span style="FONT-FAMILY: 宋体">，这就是它们的一般含义。我们可以创建一个</span><span lang="EN-US">Point</span><span style="FONT-FAMILY: 宋体">结构，表示它们：</span></p>
<p class="2" style="MARGIN-TOP: 8.15pt; MARGIN-LEFT: 21.45pt; MARGIN-RIGHT: 0cm; FTEL: 18.45pt"><a ftel="OLE_LINK3"><span lang="EN-US">Point ab = new Point(20, 10);</span></a></p>
<p class="2" style="MARGIN-TOP: 0cm; MARGIN-LEFT: 21.45pt; MARGIN-RIGHT: 0cm; FTEL: 18.45pt"><span lang="EN-US">Console.WriteLine(&quot;Moved {0} across, {1} down&quot;, ab.X, ab.Y);</span></p>
<p class="MsoNormal"><span lang="EN-US">X</span><span style="FONT-FAMILY: 宋体">和</span><span lang="EN-US">Y</span><span style="FONT-FAMILY: 宋体">都是读写属性，也可以在</span><span lang="EN-US">Point</span><span style="FONT-FAMILY: 宋体">中设置这些值：</span></p>
<p class="2" style="MARGIN-TOP: 8.15pt; MARGIN-LEFT: 21.45pt; MARGIN-RIGHT: 0cm; FTEL: 18.45pt"><span lang="EN-US">Point ab = new Point();</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US">ab.X = 20;</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US">ab.Y = 10;</span></p>
<p class="a6" style="MARGIN-TOP: 0cm; MARGIN-LEFT: 21.45pt; MARGIN-RIGHT: 0cm; FTEL: 18.45pt"><span lang="EN-US">Console.WriteLine(&quot;Moved {0} across, {1} down&quot;, ab.X, ab.Y);</span></p>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体">注意，按照惯例，水平和垂直坐标表示为</span><span lang="EN-US">x</span><span style="FONT-FAMILY: 宋体">和</span><span lang="EN-US">y(</span><span style="FONT-FAMILY: 宋体">小写</span><span lang="EN-US">)</span><span style="FONT-FAMILY: 宋体">，但相应的</span><span lang="EN-US">Point</span><span style="FONT-FAMILY: 宋体">属性是</span><span lang="EN-US">X</span><span style="FONT-FAMILY: 宋体">和</span><span lang="EN-US">Y(</span><span style="FONT-FAMILY: 宋体">大写</span><span lang="EN-US">)</span><span style="FONT-FAMILY: 宋体">，因为在</span><span lang="EN-US">C#</span><span style="FONT-FAMILY: 宋体">中，公共属性的一般约定是名称以大写字母开头。</span></p>
<p class="MsoNormal"><span lang="EN-US">PointF</span><span style="FONT-FAMILY: 宋体">与</span><span lang="EN-US">Point</span><span style="FONT-FAMILY: 宋体">完全相同，但</span><span lang="EN-US">X</span><span style="FONT-FAMILY: 宋体">和</span><span lang="EN-US">Y</span><span style="FONT-FAMILY: 宋体">属性的类型是</span><span lang="EN-US">float</span><span style="FONT-FAMILY: 宋体">，而不是</span><span lang="EN-US">int</span><span style="FONT-FAMILY: 宋体">。</span><span lang="EN-US">PointF</span><span style="FONT-FAMILY: 宋体">用于坐标不是整数值的情况。已经为这些结构定义了数据类型转换，这样就可以把</span><span lang="EN-US">Point</span><span style="FONT-FAMILY: 宋体">隐式转换为</span><span lang="EN-US"> PointF</span><span style="FONT-FAMILY: 宋体">，</span><span lang="EN-US">(</span><span style="FONT-FAMILY: 宋体">注意因为</span><span lang="EN-US">Point</span><span style="FONT-FAMILY: 宋体">和</span><span lang="EN-US"> PointF</span><span style="FONT-FAMILY: 宋体">是结构，这种转换实际上涉及到数据的复制</span><span lang="EN-US">)</span><span style="FONT-FAMILY: 宋体">。但没有相应的逆过程，要把</span><span lang="EN-US">PointF</span><span style="FONT-FAMILY: 宋体">转换为</span><span lang="EN-US">Point</span><span style="FONT-FAMILY: 宋体">，必须显式地复制值，或使用下面的</span><span lang="EN-US">3</span><span style="FONT-FAMILY: 宋体">个转换方法</span><span lang="EN-US">Round()</span><span style="FONT-FAMILY: 宋体">、</span><span lang="EN-US">Truncate()</span><span style="FONT-FAMILY: 宋体">和</span><span lang="EN-US">Ceiling()</span><span style="FONT-FAMILY: 宋体">：</span></p>
<p class="2" style="MARGIN-TOP: 8.15pt; MARGIN-LEFT: 21.45pt; MARGIN-RIGHT: 0cm; FTEL: 18.45pt"><span lang="EN-US">&nbsp;&nbsp; PointF abFloat = new PointF(20.5F, 10.9F);</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US">&nbsp;&nbsp; // converting to Point</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US" style="COLOR: black">&nbsp;&nbsp; Point ab = new Point();</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US" style="COLOR: black">&nbsp;&nbsp; ab.X = (int)abFloat.X;</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US" style="COLOR: black">&nbsp;&nbsp; ab.Y = (int)abFloat.Y;</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US">&nbsp;&nbsp; Point ab1 = Point.Round(abFloat);</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US">&nbsp;&nbsp; Point ab2 = Point.Truncate(abFloat);</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US">&nbsp;&nbsp; Point ab3 = Point.Ceiling(abFloat);</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US">&nbsp;</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US">&nbsp;&nbsp; // but conversion back to PointF is implicit</span></p>
<p class="2" style="MARGIN-TOP: 0cm; MARGIN-LEFT: 21.45pt; MARGIN-RIGHT: 0cm; FTEL: 18.45pt"><span lang="EN-US" style="COLOR: black">&nbsp;&nbsp; PointF abFloat2 = ab;</span></p>
<p class="MsoNormal" style="LINE-HEIGHT: 17.6pt"><span style="FONT-FAMILY: 宋体">下面看看测量单位。在默认情况下，</span><span lang="EN-US">GDI+</span><span style="FONT-FAMILY: 宋体">把单位看作是屏幕</span><span lang="EN-US">(</span><span style="FONT-FAMILY: 宋体">或打印机，无论图形设备是什么，都可以这样认为</span><span lang="EN-US">)</span><span style="FONT-FAMILY: 宋体">上的像素，这就是</span><span lang="EN-US">Graphics</span><span style="FONT-FAMILY: 宋体">对象方法把它们接收到的坐标看作其参数的方式。例如，点</span><span lang="EN-US">new Point(20,10)</span><span style="FONT-FAMILY: 宋体">表示在屏幕上水平移动</span><span lang="EN-US">20</span><span style="FONT-FAMILY: 宋体">个像素，向下垂直移动</span><span lang="EN-US">10</span><span style="FONT-FAMILY: 宋体">个像素。通常这些像素从窗口客户区域的左上角开始测量，如上面的示例所示。但是，情况并不总是如此。例如，在某些情况下，需要以窗口的左上角</span><span lang="EN-US">(</span><span style="FONT-FAMILY: 宋体">包括其边框</span><span lang="EN-US">)</span><span style="FONT-FAMILY: 宋体">为原点来绘图，甚至以屏幕的左上角为原点。但在大多数情况下，除非文档说明书说明，否则都可以假定像素值是相对于客户区域的左上角。</span></p></div>
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                        <h1 id="divCurrentNode2" style="color: #b83507; width: 100%; text-align: left; font-size: 12px; padding-left: 2px">当前章节:<a href='100165565.htm'><font color='red'>20.2.1  Point和PointF结构</font></a></h1>
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                        <div style='float:left;width:49%'>·<a href='100165562.htm'>20.1.3  使用OnPaint()绘制图形</a></div><div style='float:right;width:49%'>·<a href='100165563.htm'>20.1.4  使用剪切区域</a></div><div style='float:left;width:49%'>·<a href='100165564.htm'>20.2  测量坐标和区域</a></div><div style='float:right;width:49%'>·<a href='100165566.htm'>20.2.2  Size和SizeF结构</a></div><div style='float:left;width:49%'>·<a href='100165567.htm'>20.2.3  Rectangle和RectangleF结构</a></div><div style='float:right;width:49%'>·<a href='100165568.htm'>20.2.4  Region</a></div></div>
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