关于LineDDA函数(主要是关于其是否有绘图操作)

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关于该函数的原型及参数可以参考msdn：

The LineDDA function determines which pixels should be highlighted for a line defined by the specified starting and ending points.（指定由给定的起点和终点定义的线段上应该被“高亮”的像素）这个“高亮（highlighted）”用的很奇怪，让人不知道是什么意思，是不是要画线的意思？

BOOL LineDDA(  int nXStart,             // x-coordinate of starting point  int nYStart,             // y-coordinate of starting point  int nXEnd,               // x-coordinate of ending point  int nYEnd,               // y-coordinate of ending point  LINEDDAPROC lpLineFunc,  // callback function  LPARAM lpData            // application-defined data);

Parameters

nXStart: [in] Specifies the x-coordinate, in logical units, of the line's starting point.
nYStart: [in] Specifies the y-coordinate, in logical units, of the line's starting point.
nXEnd: [in] Specifies the x-coordinate, in logical units, of the line's ending point.
nYEnd: [in] Specifies the y-coordinate, in logical units, of the line's ending point.
lpLineFunc: [in] Pointer to an application-defined callback function. For more information, see the LineDDAProc callback function.
lpData: [in] Pointer to the application-defined data.

LineDDA函数不会绘制直线，仅仅是调用回调函数。这个是我一直不能确定的问题，经过查阅资料和实例操作才得出这样的结论的。该函数使用Bre画直线算法求出直线上的点坐标，每计算出一个坐标，就将其和程序定义的数据lpData传送给回调函数lpLineFunc，由回调函数完成相应的操作。

下面给出一个示例程序：

建立一个MFC应用程序；
在函数OnDraw中添加如下代码：void CSimpleView::OnDraw(CDC* pDC){ //Implementation Note: it is safe to pass our local reference //of the pDC object because all of the callbacks will complete //before the pDC goes out of scope. CSimpleDoc* pDoc = GetDocument(); ASSERT_VALID(pDoc); //Draw a Line pDC->MoveTo(10,10); pDC->LineTo(300,300); //Use LineDDA to Draw 0's at intervals along the line. ::LineDDA(10,10,300,300,(LINEDDAPROC)DrawZero,(long)pDC); }
添加回调函数代码如下：VOID CALLBACK DrawZero(int X,int Y,LPARAM lpData){ //This Callback routine will be called for every calculated //point in the line. //Implementation Note: Use lpData to pass a reference to a //CDC object for drawing. CDC* pDC; pDC = (CDC*)lpData; if( X % 20 ==0) { pDC->TextOut(X,Y,_T("0")); } }
运行结果：