mFC 橡皮线

一般都用GDI实现:

 

void CXiangpijinView::OnMouseMove(UINT nFlags, CPoint point) 
{
    // TODO: Add your message handler code here and/or call default
    
    CView::OnMouseMove(nFlags, point);
    if (Lbrndown)
    {


          CClientDC dc(this);
         int oldmode=dc.SetROP2(R2_NOTXORPEN);
         CPen pen(PS_SOLID, 2.0, RGB(255,0,0)), *oldpen;
         oldpen = dc.SelectObject(&pen);
         
         dc.MoveTo(m_ptOrigin);
         dc.LineTo(m_ptEnd);
         
         m_ptEnd=point;
         
         dc.MoveTo(m_ptOrigin);
         dc.LineTo(m_ptEnd);
         
         dc.SelectObject(oldpen);
         dc.SetROP2(oldmode);
         ReleaseDC(&dc);
        

    }
    
}

void CXiangpijinView::OnLButtonDown(UINT nFlags, CPoint point) 
{
    // TODO: Add your message handler code here and/or call default
    
    CView::OnLButtonDown(nFlags, point);
    Lbrndown=true;
    m_ptOrigin = m_ptEnd = point; 
}

主要得益于GDI支持SetROP2,绘图模式。

nDrawMode Specifies the new drawing mode. It can be any of the following values:

R2_BLACK   Pixel is always black.

R2_WHITE   Pixel is always white.

R2_NOP   Pixel remains unchanged.

R2_NOT   Pixel is the inverse of the screen color.

R2_COPYPEN   Pixel is the pen color.

R2_NOTCOPYPEN   Pixel is the inverse of the pen color.

R2_MERGEPENNOT   Pixel is a combination of the pen color and the inverse of the screen color (final pixel = (NOT screen pixel) OR pen).

R2_MASKPENNOT   Pixel is a combination of the colors common to both the pen and the inverse of the screen (final pixel = (NOT screen pixel) AND pen).

R2_MERGENOTPEN   Pixel is a combination of the screen color and the inverse of the pen color (final pixel = (NOT pen) OR screen pixel).

R2_MASKNOTPEN   Pixel is a combination of the colors common to both the screen and the inverse of the pen (final pixel = (NOT pen) AND screen pixel).

R2_MERGEPEN   Pixel is a combination of the pen color and the screen color (final pixel = pen OR screen pixel).

R2_NOTMERGEPEN   Pixel is the inverse of the R2_MERGEPEN color (final pixel = NOT(pen OR screen pixel)).

R2_MASKPEN   Pixel is a combination of the colors common to both the pen and the screen (final pixel = pen AND screen pixel).

R2_NOTMASKPEN   Pixel is the inverse of the R2_MASKPEN color (final pixel = NOT(pen AND screen pixel)).

R2_XORPEN   Pixel is a combination of the colors that are in the pen or in the screen, but not in both (final pixel = pen XOR screen pixel).

R2_NOTXORPEN   Pixel is the inverse of the R2_XORPEN color (final pixel = NOT(pen XOR screen pixel)).

 

原理:R2_NOTXORPEN画出来的颜色与R2_XORPEN相反,R2_XORPEN是屏幕颜色和画笔颜色的异或。OnMouseMove第一次被调用时,还没画线,所以屏幕的颜色是白色的,R2_XORPEN是当前画笔的颜色取反,那么R2_NOTXORPEN就是当前画笔颜色了。就是说第一次画的线是画笔的颜色。

第二次调用OnMouseMove时,m_ptOrigin和m_ptEnd两个点还没变,所以可以用这两个点再画线,将第一次画的线覆盖掉,变成画布的颜色,然后在新的point点和m_ptOrigin之间重新画线,颜色为画笔颜色。在旧的直线上面画线,因为线本来有颜色,所以R2_XORPEN(屏幕的颜色==画笔颜色)就会变成黑色(1 xor 1=0,0 xor 0=0),取反,即R2_NOTXORPEN为白色,就是画布的颜色,看起来就像消失了一样,其实只不过是线变成白色了(如果画笔不是白色,比如使用你系统设置了护眼配色,客户区变成不伤眼的浅绿色,这样显示出来的颜色还是白色,而不是客户区的颜色)。旧的直线删除了,就可以在新的点point上再次画线了。

注意:如果背景色是白色,那么画出来的线就是画笔的颜色,如果不是白色,线的颜色为笔色与屏幕颜色异或再取反的颜色。

同理只需替换绘图函数就可可以实现矩形、椭圆的橡皮筋效果。

 

而GDI+不支持SetRop2,

好像说是因为SetRop2只针对光栅,而GDI+不只是用于光栅,要支持打印机等原因。不懂。

一般来说,新的库应该有方法来取代SetRopt2原来的功能。

这就使得画橡皮条非常困难,网上提供了一些方法以及问题:

1/ 使用DllImport,导入SetRop2  : 结合GDI绘图,这违背了GDI+删去SetRop2的本意。

2/ 更新从起始点到结束点的整个块状区域 : 我觉得为了一条线而刷新整个区域是很愚蠢的事情,虽然可以使用双缓冲等等技术

3/ 使用一个ErasePen和一个DrawPen,ErasePen和背景同色 : 这个方法很有问题,当和其他线条相交时会擦去原来的线条

不知道为什么要把SetRop2去掉。

我自己实现的使用双缓冲来实现橡皮条

 

void CXiangpijinView::OnDraw(CDC* pDC)
{
    CXiangpijinDoc* pDoc = GetDocument();
    ASSERT_VALID(pDoc);
    // TODO: add draw code for native data here

    GetClientRect(&rc);
    Graphics Gp(pDC->m_hDC);
    SolidBrush mybrush(Color( 135 ,135,135));
    Gp.FillRectangle(&mybrush,0,0,rc.Width(),rc.Height());
    Gp.ReleaseHDC(hMemDC);
    
    HBITMAP hBitmap,hOldBitmap;    
    //建立一个屏幕设备环境句柄    
    hMemDC=CreateCompatibleDC(pDC->m_hDC);
    //建立一个与屏幕设备环境句柄兼容、与鼠标指针所在窗口的区域等大的位图
    hBitmap=CreateCompatibleBitmap(pDC->m_hDC,rc.Width(),rc.Height());
    //把新位图选到内存设备描述表中
    hOldBitmap=(HBITMAP)SelectObject(hMemDC,hBitmap);
    //把屏幕设备描述表拷贝到内存设备描述表中    
    BitBlt(hMemDC,0,0,rc.Width(),rc.Height(),pDC->m_hDC,0,0,SRCCOPY);

}
void CXiangpijinView::OnMouseMove(UINT nFlags, CPoint point) 
{
    // TODO: Add your message handler code here and/or call default
    
    CView::OnMouseMove(nFlags, point);
    if (Lbrndown)
    {


        BitBlt(GetDC()->m_hDC,0,0,rc.Width(),rc.Height(),hMemDC,0,0,SRCCOPY);
   Graphics Gp3(GetDC()->m_hDC);
        Pen mypen(Color(0,255,0),2.0);
   Gp3.DrawLine(&mypen,m_ptOrigin.x,m_ptOrigin.y,point.x,point.y);  
     Gp3.ReleaseHDC(GetDC()->m_hDC);
} } void CXiangpijinView::OnLButtonDown(UINT nFlags, CPoint point) { // TODO: Add your message handler code here and/or call default CView::OnLButtonDown(nFlags, point); Lbrndown=true; m_ptOrigin = m_ptEnd = point; } void CXiangpijinView::OnLButtonUp(UINT nFlags, CPoint point) { // TODO: Add your message handler code here and/or call default CView::OnLButtonUp(nFlags, point); //把新的DC拷贝到hMemDC BitBlt(hMemDC,0,0,rc.Width(),rc.Height(),GetDC()->m_hDC,0,0,SRCCOPY); }

主要原理是绘图前把屏幕DC内容拷贝到兼容的内存位图中,绘图时把兼容dC 上的内容拷贝到屏幕,然后在在当前DC上绘图,一次绘制结束再把 DC上拷贝到兼容DC上。


常用绘图操作

 m_map = new Bitmap(rc.Width(),rc.Height());  

Pen mypen(Color(0,255,0),2.0);  

m_Gpp = new Graphics(m_map);  

m_Gpp->DrawEllipse(&mypen,po.X,po.Y,8.0,8.0);

Graphics Gp3(GetDC()->m_hDC);  

Gp3.DrawImage(m_map,0,0);

 Gp3.ReleaseHDC(GetDC()->m_hDC);

 

 

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