内存DC的问题

[dfyang]

在OnDraw中的代码如下：
CRect rect;
GetClientRect(&rect);
m_rectCurve=rect;

CDC memDC;
memDC.CreateCompatibleDC(pDC);
memDC.FillSolidRect(&rect,RGB(0,0,0));
DrawBkGround(&memDC);
DrawCurve(&memDC);

pDC->BitBlt( rect.left, rect.top, rect.Width(), rect.Height(), &memDC, 0, 0, SRCCOPY );

结果是什么也没画出来，不知道为什么？

[dfyang]

不会吧，没人知道？

[waterpub]

创建一个bitmap选到memdc里面，不然你的图形怎么画到memdc呢？
CRect rect;
GetClientRect(&rect);
m_rectCurve=rect;

CDC memDC;
memDC.CreateCompatibleDC(pDC);
memDC.FillSolidRect(&rect,RGB(0,0,0));
CBitmap* m_bitmap;
CBitmap* m_OldBitmap;
m_bitmap = new CBitmap();
m_OldBitmap = (cbitmap*)memdc.selectobject(m_bitmap);
DrawBkGround(&memDC);
DrawCurve(&memDC);

pDC->BitBlt( rect.left, rect.top, rect.Width(), rect.Height(), &memDC, 0, 0, SRCCOPY );


m_bitmap.deleteobject();

[dfyang]

嗯，自己先搞定了，正如楼主所说的一样。还是要感谢楼主的热心帮忙

[sjcode]

没错，你首先得建一张空的位图，把它选入这个memDC里。

然后才能在上面绘制.

HDC hDC = ::GetDC(m_hWnd);

HDC hbmpDC = CreateCompatibleDC(hDC);
HBITMAP hOldBitmap = (HBITMAP)::SelectObject(hbmpDC,m_Background);
BitBlt(hDC,0,0,bm.bmWidth,bm.bmHeight,hbmpDC,0,0,SRCCOPY);
SelectObject(hDC,hOldBitmap);
DeleteObject(hbmpDC);

HPEN hPen = ::CreatePen(PS_DASH,10,RGB(128,128,128));
HPEN hOldPen = (HPEN)SelectObject(hDC,hPen);

MoveToEx(hDC,20,20,NULL);
LineTo(hDC , 100 , 100);

SelectObject(hDC,hOldPen);
DeleteObject(hPen);
::ReleaseDC(m_hWnd,hDC);