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<p><small><a href="../../../index.htm">首頁(yè)</a> >> <a href="../../program.htm">程序設(shè)計(jì)</a>
>> <a href="../cbuilder.htm">C++ Builder</a> >> </small>圖形程式設(shè)計(jì)基本觀念·<font color="#000000">范例四</font></p>
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<p align="left"><font SIZE="2" color="#FF0000">·范例四的輸出</font></p>
<p><font SIZE="2"><img SRC="Image4.gif" WIDTH="458" HEIGHT="344">圖04</font></p>
<font SIZE="2">
<p>void __fastcall TForm1::FormPaint(TObject *Sender)</p>
<p>{</p>
<p> double A,x1,y1,x2,y2;</p>
<p> int D=80;</p>
<p> double E,F;</p>
<p> for (int i=0; i<960; i++)</p>
<p> {</p>
<p> A = i*M_PI/480;</p>
<p> E = D*(1+cos(20*A)/4);</p>
<p> F = E*(1+sin(4*A));</p>
<p> x1 = 320+F*cos(A);</p>
<p> x2 = 320+F*cos(A+M_PI/5);</p>
<p> y1 = 240-F*sin(A);</p>
<p> y2 = 240-F*sin(A+M_PI/5);</p>
<p> Canvas->MoveTo(x1,y1);</p>
<p> Canvas->LineTo(x2,y2);</p>
<p> }</p>
<p>}</p>
<p>以上四個(gè)范例程式是我先為你準(zhǔn)備的開(kāi)胃小菜，主要用以說(shuō)明C++Builder
的Canvas繪圖基本觀念，同時(shí)也讓你明了：利用幾個(gè)簡(jiǎn)單的基本函式也可以做出美麗的電腦繪圖。</p>
<p>03 TCanvas的Handle性質(zhì)</p>
<p>在平時(shí)，你不太會(huì)有機(jī)會(huì)用到TCanvas的Handle性質(zhì)，它其實(shí)就是在Windows
SDK繪圖函式中都必須要用到的DC (Device Context)值。在Windows系統(tǒng)中，所有的繪圖動(dòng)作都必須透過(guò)DC來(lái)達(dá)成，</p>
<p>舉例來(lái)說(shuō)標(biāo)準(zhǔn)的SDK畫線函式應(yīng)該是這樣的 </p>
<p>BOOL LineTo(</p>
<p> HDC hdc, // device context handle </p>
<p> int nXEnd, // x-coordinate of line's ending point </p>
<p> int nYEnd // y-coordinate of line's ending point </p>
<p>);</p>
<p>因此在C++Builder中，使用Casvas->LineTo(x,y) 來(lái)繪圖和呼叫標(biāo)準(zhǔn)SDK函式的LineTo((HDC)Canvas->Handle,x,y)
是一樣的。</p>
<p>當(dāng)然我不建議你在C++Builder中使用SDK語(yǔ)法來(lái)畫圖，但是我還是希望你對(duì)它們兩者之間的關(guān)系有一些了解，因?yàn)镃++Builder的VCL雖然在Canvas中已經(jīng)把大部份的繪圖函式實(shí)作出來(lái)，以物件的方式提供你使用，不過(guò)若是你要使用到Canvas未提供的繪圖函式時(shí)，你就可以利用Canvas->Handle來(lái)做為傳入SDK函式的參數(shù)。</p>
<p>04 TCanvas的TPen 性質(zhì)</p>
<p>注：SDK加油站。</p>
<p>在SDK中使用Pen的方式是利用SelectObject函式來(lái)達(dá)成。它傳入兩個(gè)參數(shù)，一個(gè)是HDC值，它就是Canvas->Handle值，另一個(gè)則是HGDIOBJ值，它是一些繪圖工具的通稱，以Pen而言，它就是HPEN值，同時(shí)也是Pen->Handle值。</p>
<p>HGDIOBJ SelectObject(</p>
<p>HDC hdc, // handle of device context </p>
<p>HGDIOBJ hgdiobj // handle of object </p>
<p>);</p>
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<p><font SIZE="2">·<small><a href="../../../index.htm">首頁(yè)</a> >>
<a href="../../program.htm">程序設(shè)計(jì)</a> >> <a href="../cbuilder.htm">C++
Builder</a> >> </small>圖形程式設(shè)計(jì)基本觀念·</font><font SIZE="2" color="#000000">范例四</font></p>
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