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<p style="FTEL: 8.15pt" align="center"><span style="COLOR: black; FONT-FAMILY: 宋体">图</span><span lang="EN-US" style="COLOR: black"> 20-11</span></p>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体">为了使该图更清晰，我们向下向右扩展了该文档，超出了屏幕的边界，但这不会改变我们的推论，我们还假定其上还有一个水平滚动条和一个垂直滚动条。</span></p>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体">在该图中，细矩形标记了屏幕区域的边框和整个文档的边框。粗线条标记试图要绘制的矩形和椭圆。</span><span lang="EN-US">P</span><span style="FONT-FAMILY: 宋体">标记要绘制的某个随意点，这个点在后面会作为一个示例。在调用绘图方法时，提供</span><span lang="EN-US">graphics</span><span style="FONT-FAMILY: 宋体">实例和从</span><span lang="EN-US">B</span><span style="FONT-FAMILY: 宋体">点到</span><span lang="EN-US">P</span><span style="FONT-FAMILY: 宋体">点的矢量，这个矢量表示为一个</span><span lang="EN-US">Ponit</span><span style="FONT-FAMILY: 宋体">实例。我们实际上需要给出从点</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">的矢量。</span></p>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体">问题是，我们不知道从</span><span lang="EN-US">A</span><span style="FONT-FAMILY: 宋体">点到</span><span lang="EN-US">P</span><span style="FONT-FAMILY: 宋体">点的矢量。而知道从</span><span lang="EN-US">B</span><span style="FONT-FAMILY: 宋体">点到</span><span lang="EN-US">P</span><span style="FONT-FAMILY: 宋体">点的矢量，这是</span><span lang="EN-US">P</span><span style="FONT-FAMILY: 宋体">相对于文档左上角的坐标<span style="LETTER-SPACING: -1pt">——</span></span><span style="LETTER-SPACING: -1pt"> </span><span style="FONT-FAMILY: 宋体">我们要在文档的</span><span lang="EN-US">P</span><span style="FONT-FAMILY: 宋体">点绘图。还知道从</span><span lang="EN-US">B</span><span style="FONT-FAMILY: 宋体">点到</span><span lang="EN-US">A</span><span style="FONT-FAMILY: 宋体">点的矢量，这是滚动的距离，它存储在</span><span lang="EN-US">Form</span><span style="FONT-FAMILY: 宋体">类的一个属性</span><span lang="EN-US">AutoScrollPosition</span><span style="FONT-FAMILY: 宋体">中。但是不知道从</span><span lang="EN-US">A</span><span style="FONT-FAMILY: 宋体">点到</span><span lang="EN-US">P</span><span style="FONT-FAMILY: 宋体">点的矢量。</span></p>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体">现在如果您还记得高中的数学知识，就知道得到该矢量的解决方案</span><span lang="EN-US" style="LETTER-SPACING: -1pt">—— </span><span style="FONT-FAMILY: 宋体">只需进行矢量相减即可。例如，要从</span><span lang="EN-US">B</span><span style="FONT-FAMILY: 宋体">点到</span><span lang="EN-US">P</span><span style="FONT-FAMILY: 宋体">点，可以水平移动</span><span lang="EN-US">150</span><span style="FONT-FAMILY: 宋体">个像素，垂直向下移动</span><span lang="EN-US">200</span><span style="FONT-FAMILY: 宋体">个像素。而要从</span><span lang="EN-US">B</span><span style="FONT-FAMILY: 宋体">点到</span><span lang="EN-US">A</span><span style="FONT-FAMILY: 宋体">点，就需要水平移动</span><span lang="EN-US">10</span><span style="FONT-FAMILY: 宋体">个像素，垂直向下移动</span><span lang="EN-US">57</span><span style="FONT-FAMILY: 宋体">个像素。这表示，要从</span><span lang="EN-US">A</span><span style="FONT-FAMILY: 宋体">点到</span><span lang="EN-US">P</span><span style="FONT-FAMILY: 宋体">点，需要水平移动</span><span lang="EN-US">140</span><span style="FONT-FAMILY: 宋体">个像素</span><span lang="EN-US">(</span><span style="FONT-FAMILY: 宋体">＝</span><span lang="EN-US">150–10)</span><span style="FONT-FAMILY: 宋体">，垂直向下移动</span><span lang="EN-US">143</span><span style="FONT-FAMILY: 宋体">个像素</span><span lang="EN-US">(</span><span style="FONT-FAMILY: 宋体">＝</span><span lang="EN-US">200–57)</span><span style="FONT-FAMILY: 宋体">。为了使之更简单，</span><span lang="EN-US">Graphics</span><span style="FONT-FAMILY: 宋体">类执行了一个方法来进行这些计算，这个方法是</span><span lang="EN-US">TranslateTransform</span><span style="FONT-FAMILY: 宋体">，我们给它传送水平和垂直坐标，表示客户区域的左上角相对于文档的左上角</span><span lang="EN-US">(AutoScrollPosition</span><span style="FONT-FAMILY: 宋体">属性，它是图中从</span><span lang="EN-US">B</span><span style="FONT-FAMILY: 宋体">到</span><span lang="EN-US">A</span><span style="FONT-FAMILY: 宋体">的矢量</span><span lang="EN-US">)</span><span style="FONT-FAMILY: 宋体">，然后</span><span lang="EN-US">Graphics</span><span style="FONT-FAMILY: 宋体">设备考虑客户区域相对于文档区域的位置，处理这些坐标。</span></p>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体">解释完之后，所需做的是把下面这行代码添加到绘图代码中：</span></p>
<p class="2" style="MARGIN-TOP: 8.15pt; MARGIN-LEFT: 21.45pt; MARGIN-RIGHT: 0cm; FTEL: 18.45pt"><span lang="EN-US">dc.TranslateTransform(this.AutoScrollPosition.X, this.AutoScrollPosition.Y);</span></p>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体">实际上在本示例中，它有点复杂，因为我们还要分别测试剪切区域，看看是否需要进行绘制工作。需要调整这个测试，把滚动的位置也考虑在内。完成后，该示例的整个绘图代码如下所示：</span></p>
<p class="2" style="MARGIN-TOP: 8.15pt; MARGIN-LEFT: 21.45pt; MARGIN-RIGHT: 0cm; FTEL: 18.45pt"><span lang="EN-US"> protected override void OnPaint( PaintEventArgs e )</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> {</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> base.OnPaint(e);</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> Graphics dc = e.Graphics;</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> Size scrollOffset = new Size(this.AutoScrollPosition);</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> if (e.ClipRectangle.Top+scrollOffset.Width < 350 || </span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> e.ClipRectangle.Left+scrollOffset.Height < 250)</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> {</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> Rectangle rectangleArea = new Rectangle</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> (rectangleTopLeft+scrollOffset, rectangleSize);</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> Rectangle ellipseArea = new Rectangle</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> (ellipseTopLeft+scrollOffset, ellipseSize);</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> dc.DrawRectangle(bluePen, rectangleArea);</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> dc.DrawEllipse(redPen, ellipseArea);</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> }</span></p>
<p class="2" style="MARGIN-TOP: 0cm; MARGIN-LEFT: 21.45pt; MARGIN-RIGHT: 0cm; FTEL: 18.45pt"><span lang="EN-US"> }</span></p>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体">现在，滚动代码工作正常，最后得到正确的滚动屏幕图，如图</span><span lang="EN-US">20-12</span><span style="FONT-FAMILY: 宋体">所示。</span></p>
<p align="center"><span lang="EN-US"><img height="193" src="20/image013.jpg" width="201" alt="" /></span></p>
<p style="FTEL: 8.15pt" align="center"><span style="COLOR: black; FONT-FAMILY: 宋体">图</span><span lang="EN-US" style="COLOR: black"> 20-12</span></p>
<p class="a3" style="MARGIN-TOP: 8.15pt; FTEL: 21.45pt"><a ftel="_Toc507815364"><span style="FONT-FAMILY: 黑体">世界、页面和设备坐标</span></a></p>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体">测量相对于文档区域左上角的位置和测量相对于屏幕</span><span lang="EN-US">(</span><span style="FONT-FAMILY: 宋体">桌面</span><span lang="EN-US">)</span><span style="FONT-FAMILY: 宋体">左上角的位置之间的区别非常重要，</span><span lang="EN-US">GDI+</span><span style="FONT-FAMILY: 宋体">为它们指定了不同的名称：</span></p>
<p class="1" style="MARGIN-LEFT: 37.25pt; FTEL: -15.8pt"><span lang="EN-US" style="LETTER-SPACING: -0.1pt">●<span style="FONT: 7pt 'Times New Roman'"> </span></span><span style="FONT-FAMILY: 宋体; LETTER-SPACING: -0.1pt">世界坐标</span><span lang="EN-US" style="LETTER-SPACING: -0.1pt">(World Coordinate)</span><span style="FONT-FAMILY: 宋体; LETTER-SPACING: -0.1pt">：是要测量的点距离文档区域左上角的位置</span><span lang="EN-US" style="LETTER-SPACING: -0.1pt">(</span><span style="FONT-FAMILY: 宋体; LETTER-SPACING: -0.1pt">以像素为单位</span><span lang="EN-US" style="LETTER-SPACING: -0.1pt">)</span><span style="FONT-FAMILY: 宋体; LETTER-SPACING: -0.1pt">。</span></p>
<p class="1" style="MARGIN-LEFT: 37.55pt; FTEL: -16.1pt"><span lang="EN-US">●<span style="FONT: 7pt 'Times New Roman'"> </span></span><span style="FONT-FAMILY: 宋体">页面坐标</span><span lang="EN-US">(Page Coordinate)</span><span style="FONT-FAMILY: 宋体">：是要测量的点距离客户区域左上角的位置</span><span lang="EN-US">(</span><span style="FONT-FAMILY: 宋体">以像素为单位</span><span lang="EN-US">)</span><span style="FONT-FAMILY: 宋体">。</span></p>
<p class="a3" style="MARGIN-TOP: 8.15pt; FTEL: 21.45pt"><span style="FONT-FAMILY: 黑体">注意：</span></p>
<p class="a1" style="FTEL: 21.45pt"><span style="FONT-FAMILY: 楷体_GB2312">熟悉</span><span lang="EN-US">GDI</span><span style="FONT-FAMILY: 楷体_GB2312">的开发人员要注意，世界坐标对应于</span><span lang="EN-US">GDI</span><span style="FONT-FAMILY: 楷体_GB2312">中的逻辑坐标。页面坐标对应于设备坐标。还要注意，编写逻辑和设备坐标之间的转换代码在</span><span lang="EN-US">GDI+</span><span style="FONT-FAMILY: 楷体_GB2312">中有了变化。在</span><span lang="EN-US">GDI</span><span style="FONT-FAMILY: 楷体_GB2312">中，转换是使用</span><span lang="EN-US">Windows API</span><span style="FONT-FAMILY: 楷体_GB2312">函数</span><span lang="EN-US">LPtoDP()</span><span style="FONT-FAMILY: 楷体_GB2312">和</span><span lang="EN-US">DPtoLP()</span><span style="FONT-FAMILY: 楷体_GB2312">通过设备环境进行的，而在</span><span lang="EN-US">GDI+</span><span style="FONT-FAMILY: 楷体_GB2312">中，由派生于</span><span lang="EN-US">Form</span><span style="FONT-FAMILY: 楷体_GB2312">和各种</span><span lang="EN-US">Windows </span><span style="FONT-FAMILY: 楷体_GB2312">窗体控件设备的</span><span lang="EN-US">Control</span><span style="FONT-FAMILY: 楷体_GB2312">类来维护转换过程中所需要的信息。</span></p>
<p class="MsoNormal"><span lang="EN-US">GDI+</span><span style="FONT-FAMILY: 宋体">还有第</span><span lang="EN-US">3</span><span style="FONT-FAMILY: 宋体">种坐标，即设备坐标</span><span lang="EN-US">(Device Coordinate)</span><span style="FONT-FAMILY: 宋体">。设备坐标类似于页面坐标，但其测量单位不是像素，而是用户通过调用</span><span lang="EN-US">Graphics.PageUnit</span><span style="FONT-FAMILY: 宋体">属性指定的单位。它可以使用的单位除了默认的像素外，还包括英寸和毫米。本章虽然没有使用</span><span lang="EN-US">PageUnit</span><span style="FONT-FAMILY: 宋体">属性，但它可用作获取设备的不同像素密度的方式。例如，在大多数监视器上，</span><span lang="EN-US">100</span><span style="FONT-FAMILY: 宋体">像素大约是</span><span lang="EN-US">1</span><span style="FONT-FAMILY: 宋体">英寸。但是，激光打印机可以达到</span><span lang="EN-US">1200 dpi(</span><span style="FONT-FAMILY: 宋体">点</span><span lang="EN-US">/</span><span style="FONT-FAMILY: 宋体">英寸</span><span lang="EN-US">)<span style="LETTER-SPACING: -1pt">—— </span></span><span style="FONT-FAMILY: 宋体">这表示一个</span><span lang="EN-US">100</span><span style="FONT-FAMILY: 宋体">像素宽的图形在该激光打印机上打印时会比较小。把单位设置为英寸，指定图形为</span><span lang="EN-US">1</span><span style="FONT-FAMILY: 宋体">英寸宽，就可以确保图形在不同的设备上有相同的大小。</span></p></div>
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<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 style='float:left;width:49%'>·<a href='100165569.htm'>20.3 调试须知</a></div><div style='float:right;width:49%'>·<a href='100165571.htm'>20.5 颜色</a></div><div style='float:left;width:49%'>·<a href='100165572.htm'>20.5.1 红绿蓝(RGB)值</a></div><div style='float:right;width:49%'>·<a href='100165573.htm'>20.5.2 命名的颜色</a></div></div>
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