Memory DC problem? Everyone, please help ...

守望爱情

I made a drawing program, using memory DC, the original code is as follows: (in the OnDraw (CDC * pDC) function of C * View) ----- but after running, the entire View area is black?

CDC dc;
CDC * pDrawDC = pDC;
CBitmap bitmap;
CBitmap * pOldBitmap;

CRect rect;
GetClientRect (&rect);
// ==================================================== =========
if (dc.CreateCompatibleDC (pDC))
{
if (bitmap.CreateCompatibleBitmap (pDC,
rect.Width (),
rect.Height ()))
{
OnPrepareDC (&dc, NULL);
pDrawDC =&dc;
pOldBitmap = dc.SelectObject (&bitmap);
}
}
// ==================================================== =========
pDoc-> Draw (pDrawDC, ViewID);
pDrawDC-> TextOut (1,1, * str);
dc.DPtoLP (&rect);
// ==================================================== =========
if (pDrawDC! = pDC)
{
pDC-> BitBlt (0, 0, rect.Width (), rect.Height (),
&dc, 0, 0, SRCCOPY);
dc.SelectObject (pOldBitmap);
bitmap.DeleteObject ();
}
Please help me, what is the problem?

lplp80131

The original bitmap created with CreateCompatibleBitmap is black and white
The bitmap file should be loaded directly by loadimage, then
selectobject memory dc is enough

yangxiaozhi110

The bitmap created by CreateCompatibleBitmap is black by default. Before drawing up, you must paint it with the background color you want, such as white.

mac1234

S upstairs is right!
Use CreateCompatibleBitmap to create the original bitmap, the default is black and white

守望爱情

Let’s ask a more vegetable question: how to paint the background color of the bitmap to white?

守望爱情

The reason is that I have a SetMapMode(MM_TWIPS) statement in OnPrepareDC(); when I comment out this statement, normal results can be obtained. Why?