Drawing speed

_Flaviu

Hi everybody. I trying to draw an overlay over a CDib bitmap:

///*//// Draw the bitmap ////////////////////////////////////////////////////////////////
CSize sizeDoc = pDoc->GetDib()->GetDimensions();
int cx = (int)((float)sizeDoc.cx * m_fZoomFactor);
int cy = (int)((float)sizeDoc.cy * m_fZoomFactor);
CSize sizeLog(cx, cy);
CBitmap bmp;
bmp.CreateCompatibleBitmap(pDC, sizeLog.cx, sizeLog.cy); // create background bitmap
CDC MemDC;
MemDC.CreateCompatibleDC(pDC); // create memory device context
CBitmap* pOldBitmap = MemDC.SelectObject(&bmp); // select background into memory device context
pDoc->GetDib()->Draw(&MemDC, CPoint(0,0), sizeLog); // draw content of dib into memory device context
DrawOverlay(&MemDC, pDC); // draw overlay (inline method)
pDC->BitBlt(0, 0, sizeLog.cx, sizeLog.cy, &MemDC, 0, 0, SRCCOPY); // switch memory device context to real device context
pDC->SelectObject(pOldBitmap); // select old bitmap
///*/////////////////////////////////////////////////////////////////////////////////////

and everything goes well, except when user try to drag the view, while view goes slowly ... why ? (That behaviour is more visible when the picture is a little bit zoomed)How can I speed up the code from above ? Or, what I'm doing wrong ? I have here[^] a simple sample project .... Thank you.

chaau

The problem is with this line:

pDoc->GetDib()->Draw(&MemDC, CPoint(0,0), sizeLog);

You need to replace it with another BitBlt that will copy stuff to MemDC

_Flaviu

Thank you for your interest. But I don't know how can I put content of CDib (CMyDoc::m_dib) into MemDC with CDC::BitBlt(...). Can you show me a little sample here ? Will be very helpfull to me ... You can test the behaviuour from above post link.

Sivaraman Dhamodharan

Google it for "Double Buffering"

Programming Article

_Flaviu

I think that is what I'm doing above: draw everything into a memory DC, and when everything is done, show it in real DC ... I'm missing something ?

chaau

You need to create DIB (I think you have already already created it based on the code), then you need to copy the bitmap bits to the DIB's buffer using this code:

HBITMAP	hOldBitmap = NULL;

if (m\_hBitmap == NULL)
{
	m\_hBitmap = CreateDIBSection(hDC, (BITMAPINFO\*)m\_hDib, DIB\_RGB\_COLORS, &m\_lpBits, NULL, 0);
	if (m\_hBitmap == NULL)	return;
	if (m\_lpBits == NULL)
	{
		::DeleteObject(m\_hBitmap);
		m\_hBitmap = NULL;
		return;
	} // if
} // if

memcpy(m\_lpBits, ((LPBYTE)m\_hDib + \*(LPDWORD)m\_hDib + GetPaletteSize()), m\_bi.biSizeImage);

if (m\_hMemDC == NULL)
{
	m\_hMemDC = CreateCompatibleDC(hDC);
	if (m\_hMemDC == NULL)	return;
} // if

hOldBitmap = (HBITMAP)SelectObject(m\_hMemDC, m\_hBitmap);

BitBlt(hDC, dwX, dwY, m\_bi.biWidth, m\_bi.biHeight, m\_hMemDC, 0, 0, SRCCOPY);
SelectObject(m\_hMemDC, hOldBitmap);

The main part here is the memcpy. I have copied it from my program. If you can't understand what the "m_" variables are, let me know and I will explain

_Flaviu

Yes, I know what 'm_' is, (member variable), but I also saw that you have m_hMemDC, so you apply the double-buffering tehnique ? Like in this[^] application ? Anyway, I kindly thank you, I'll apply your ideea ...

_Flaviu

I make a little confusion (or big one): double bouffering use a memory device context as member variable, single buffering use a local memory device context ... thank you sirama2004. Best regards !