The bitmap created by CreateCompatibleBitmap is black by default. Before drawing up, you must paint the background color

守望爱情

As the title! ! !

zrl8668

The following example is painted with a white background
HDC hMemDC = ::CreateCompatibleDC(hdc);
if(hMemDC == NULL)
return NULL;
CSize cs(GetWidth()+GetPenWidth(),GetHeight()+GetPenWidth());
HBITMAP hBmp = ::CreateCompatibleBitmap(hdc,cs.cx,cs.cy);
         .....

HBITMAP hOldBmp =(HBITMAP) ::SelectObject(hMemDC,hBmp);
To
PatBlt(hMemDC,0,0,cs.cx,cs.cy,WHITENESS);

         ........

addforever

CDC::FillSolidRect will do

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's the problem?

守望爱情

Using CDC::FillSolidRect() does not work at all! How to do?

addforever

Impossible not to work
pOldBitmap = dc.SelectObject(&bitmap);
dc.FillSolidRect(&rect,RGB(255,255,255));

zxw8888

If you make it white, it will definitely work. No, you are wrong elsewhere, but if you want to make it into other colors, there will be a problem. I am also struggling with this problem.
You see the following code:

zxw8888

void CDBDCView::MemDraw(CDC* pDC)
{
CRect rect;
GetClientRect(rect);
CDC memDC;
CBitmap temBmp;
memDC.CreateCompatibleDC(pDC);
temBmp.CreateCompatibleBitmap(&memDC,rect.Width(),rect.Height());
CBitmap* pOldBmp=memDC.SelectObject(&temBmp);
CBrush brush(RGB(0,255,255));
CBrush* pOldBrush=memDC.SelectObject(&brush);
memDC.Rectangle(rect);
COLORREF oldColor;
oldColor=memDC.SetBkColor(RGB(255,0,0));
memDC.TextOut(100,100,"verysource");
pDC->BitBlt(rect.left,rect.top,rect.Width(),rect.Height(),&memDC,
0,0,SRCCOPY);
memDC.SelectObject(pOldBmp);
memDC.SetBkColor(oldColor);
}
The background of the font set above is red, but it is all black when displayed, and the words are covered.
The defined one can't brush
Help me explain this problem and what is the solution

naturedark

Hey, when I did it before, I loaded a 24bit bitmap
Make the bottom canvas.

meteora12

void CDBDCView::MemDraw(CDC* pDC)
{
CRect rect;
GetClientRect(rect);
   CDC memDC;
   CBitmap temBmp;
   memDC.CreateCompatibleDC(pDC);
>>>temBmp.CreateCompatibleBitmap(&memDC,rect.Width(),rect.Height());
   CBitmap* pOldBmp=memDC.SelectObject(&temBmp);
   CBrush brush(RGB(0,255,255));
   CBrush* pOldBrush=memDC.SelectObject(&brush);
   memDC.Rectangle(rect);
   COLORREF oldColor;
   oldColor=memDC.SetBkColor(RGB(255,0,0));
   memDC.TextOut(100,100,"verysource");
   pDC->BitBlt(rect.left,rect.top,rect.Width(),rect.Height(),&memDC,0,0,SRCCOPY);
   memDC.SelectObject(pOldBmp);
>>>memDC.SelectObject(pOldBrush);
   memDC.SetBkColor(oldColor);
}

FROM MSDN:
A memory DC exists only in memory. When the memory DC is created, its display surface is exactly one monochrome pixel wide and one monochrome pixel high. Before an application can use a memory DC for drawing operations, it must select a bitmap of the correct width and height into the DC.