Why slower draws on Screen with HW Accel. set to FULL?

[uus99]

I have a question regarding Slow StretchBlt when Video Full Hardware Acceleration is Enabled in WIndows XP. Here is my computer's spec, (also on a Dell P4 2gHz) AMD AthlonXP 2000+ 512MB DDR266 WD 7200 40GB HD +8MB Cache GeForce 4MX 440 64MB AGP 4x Windows XP+SP1a+All current updates Visual C++ 6 +SP5 I have noticed that when i switch off HW Acceleration that is set to NONE (Display Prop>Advanced>Troubleshoot>Video HW Acceleration>None) i get faster drawing on screen with StretchBlt upto 4-6times faster. When i switch HW Acceleration to FULL, the drawing becomes slower. Here is a sample code that opens a CAPTURE.bmp file of 360x360 pixel and StretchBlts to screen. //------------------------------------------------------- void CSlowBltDlg::OnOK() { //timer CElapsed m_el; CDC memDCLoad; CDC *pDC; CBitmap m_bmpBitmap; pDC = this->GetDC(); int x_width=360; int y_height=360; pDC->SetStretchBltMode(COLORONCOLOR); LoadBitmap(this,&memDCLoad); //start timer m_el.Begin(); pDC->StretchBlt(20,30,200,200,&memDCLoad,0,0,x_width,y_height,SRCCOPY); //end timer and show on screen m_el.End(); CString szTime; szTime.Format("Time = %.3fms", m_el.m_dElapsed*1000); pDC->TextOut(10, 10, szTime); } void LoadBitmap(CSlowBltDlg *myDlg, CDC *memDCLoad) { CDC *pDC; CBitmap m_bmpBitmap; pDC = myDlg->GetDC(); CString m_sBitmap; memDCLoad->CreateCompatibleDC(pDC); static char BASED_CODE szFilter[] = "Bitmap Files (*.bmp)|*.bmp||"; // Create the File Open Dialog CFileDialog m_ldFile(TRUE, "*.bmp", m_sBitmap, OFN_HIDEREADONLY | OFN_OVERWRITEPROMPT, szFilter); if (m_ldFile.DoModal() == IDOK) { m_sBitmap = m_ldFile.GetPathName(); HBITMAP hBitmap =(HBITMAP)::LoadImage(AfxGetInstanceHandle(),m_sBitmap,IMAGE_BITMAP,0,0, LR_LOADFROMFILE|LR_DEFAULTCOLOR); if(hBitmap) { if(m_bmpBitmap.DeleteObject()) m_bmpBitmap.Detach(); m_bmpBitmap.Attach(hBitmap); } memDCLoad->SelectObject(&m_bmpBitmap); } } //Timing requires CElapsed class available in zip file.. see below //------------------------------------------------------- With HW Acc. Full= 6.01ms With HW Acc. None= 0.8ms Isnt HW Acc. supposed to make drawing faster? Please comment. I am doing a realtime image processing program and time is crucial. My current program StretchBlts with other processing takes 252ms per frame of an image captured from somewhere (360x360 px) on a Dell Pentium 4 2Ghz with ATI Rage 64