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cellspacing="1" cellpadding="1" bgcolor="#000000"><tr bgcolor="#FFFFFF"><td width="100%" colspan="4" align="left"><table width="95%" align="center"><tr><td class="font1"><p align="center"><br><font size="3">用DELPHI中Canvas特性开发图形软件</font><br><span class="nava"><font color="#CC9933">2000-07-13· -·-</font></span></p><p><fontcolor="#ffffff"> </font>以往开发Windows图形软件大多用 ＶＣ ＋＋ 作为开发工具， ＶＣ＋＋强大的图形功能可以让程序员编制出许多优秀的与图形相关的软件。<p><fontcolor="#ffffff"> </font>ＶＣ＋＋ 中与绘图相关的函数都封装在CDC及其衍生的CClientDC,CpaintDC,CwindowDC中。 <p><fontcolor="#ffffff"> </font>Delphi中也有一个与CDC相类似的类Tcanvas,它封装了Delphi 中的绘图函数。我们可以把Delphi和VC中相同或相近的方法做个有趣的比较。<p><fontcolor="#ffffff"> </font>（一）Canvas和 CDC绘图方法比较：<p><fontcolor="#ffffff"> </font>我们可以从以下表格中看到Tcanvas和 CDC相似的函数：<pre>表 １--１Canvas方法 ＣＤＣ方法 功能Arc Arc 画一个椭圆弧Chord Chord 画一根玄。CopyRect 拷贝指定矩形区域中图象到指定矩形Draw BitBlt 拷贝位图Ellipse Ellipse 画椭圆FillRect PaintRgn 使用刷子填充一个又一个矩型FloodFill FloodFill 用当前刷子填充区域FrameRect FrameRect 画一个矩形框Lineto Lineto 画线到Moveto Moveto 移 到Pie Pie 画扇形Polygon Polygon 画多边形PolyLine PolyLine 画多根相连的线Rectangle Rectangle 画一个实心矩形RoundRect RoundRect 画一个圆角的矩形StretchDraw StretchBlt 从源图象中 移动图象到指定矩形TextWidth GetCharWidth 返回字符宽TextOut TextOut 在指定坐标写字TextRect ExtTextOut 在制定矩形中写字</pre><fontcolor="#ffffff"> </font>上表中，我们只列出部分绘图函数，详细了解，请参阅有关Delphi和VC书籍.<p><fontcolor="#ffffff"> </font>与VC++ 相类似， Delphi也提供了绘图工具，如Tpen,Tbrush等，与VC不同的是， Delphi的绘图工具封装在Tcanvas中。Delphi也提供字形及字体大小的类Tfont,下面我们用具体例子来分析它们的用法。<p><fontcolor="#ffffff"> </font>（二）用Delphi 制作Window95/NT图形软件。<p><fontcolor="#ffffff"> </font> 象使用ＶＣ 一样，我们先用Delphi的Wizard建立一个 ＳＤＩ 应用程序。Delphi 自动建立SDI 框架， 先运行一次。程序现在还不能干任何事。下一步开始添加代码。<p><fontcolor="#ffffff"> </font> 编辑主菜单。 增加Write,Draw俩个下拉菜单项。 在"Write"下增加"HelloWorld!!","Iamateacher"，"Font.."菜单项.在"Draw"下增加"Arc"，"Line"，"Polygon"，"RoundRect"，"Rectangle"，"color."，"LineStyle"，"WidthLine". 在"LineStyle"菜单下增加"Solid","Dash","Dot"，"DashDot"，"DashDotDot" 子菜单。<p><fontcolor="#ffffff"> </font>相应的在SdiForm中增加ColorDialog,FontDialog,控件。<p><fontcolor="#ffffff"> </font>在OnPaint事件中增加如下代码：<pre>procedureTSDIAppForm.FormPaint(Sender:TObject);begincanvas.FillRect(rect);{清空桌面画布}withSDIappformdoposx:=clientwidthdiv2;posy:=clientheightdiv2;{确定客户区中心点}casedetectIof1:beginsetpenstate;canvas.Ellipse(posx-50,posy-50,posx+50,posy+50);//penwidth:=oldwidth;end;{在客户区中心点画圆}2:beginsetpenstate;canvas.MoveTo(posx-60,posy-60);canvas.LineTo(posx+60,posy+60);//penwidth:=oldwidth;end;{在客户区画直线}3:beginfposx:=trunc(50*cos(pi/6));fposy:=trunc(50*sin(pi/6));setpenstate;Canvas.Polygon([Point(posx-fposy,posy-fposx),Point(posx+fposy,posy-fposx),Point(posx+50,posy),Point(posx+fposy,posy+fposx),point(posx-fposy,posy+fposx),point(posx-50,posy)]);//penwidth:=oldwidth;end;{在客户区中心点画多边形}4:beginsetpenstate;canvas.RoundRect(posx-100,posy-50,posx+100,posy+50,20,20);end;{在客户区中心点画带圆角的矩形}5:beginsetpenstate;sdiappform.Canvas.Brush.Color:=clred;canvas.Rectangle(posx-100,posy-50,posx+100,posy+50);sdiappform.Canvas.Brush.Color:=bcolor;end{在客户区中心点用红色刷子画矩形}elsebegincanvas.Font:=formfont;canvas.TextOut(30,posy,str);end;end;{写字}end;上面程序中出现的变量在事件OnCreate中初始化。procedureTSDIAppForm.FormCreate(Sender:TObject);beginstr:='';{要写在画布上的字符串}formfont:=canvas.font;{字体和大小}detectI:=0;{确定画布上出现何种图形的参数}rect:=sdiappform.ClientRect;{客户区矩形}oldwidth:=sdiappform.Canvas.Pen.Width;{最初画笔宽度}penwidth:=oldwidth;{画笔宽度}penstyle:=sdiappform.Canvas.Pen.Style;{画笔类型}pencolor:=sdiappform.Canvas.Pen.Color;{画笔颜色}bcolor:=sdiappform.Canvas.Brush.Color;{画刷颜色}end;</pre><fontcolor="#ffffff"> </font>为了减少代码，定义了一个Public过程，设定画笔。代码如下：<pre>procedureTSDIAppForm.setpenstate;beginwithsdiappform.Canvas.Pendobegincolor:=pencolor;style:=penstyle;width:=penwidth;end;end;</pre><fontcolor="#ffffff"> </font>响应每一个菜单项OnClick事件本程序设计得非常简单，如果有兴趣，读者也可以加上一些代码，完成许多复杂的工作。<pre>procedureTSDIAppForm.LineColor1Click(Sender:TObject);beginifcolordialog1.Executethenbeginpencolor:=colordialog1.Color;SdiAppForm.Canvas.Pen.Style:=psInsideFrame;ifpenwidth<1thenSdiAppForm.Canvas.Pen.Width:=3;SdiAppForm.Canvas.Pen.Color:=pencolor;invalidate;end;end;{完成画笔颜色设定}//{完成画笔笔形设定}procedureTSDIAppForm.Solid1Click(Sender:TObject);begin⌨️ 快捷键说明
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