class CMemDCEx : public CDC
{
public:
CMemDCEx(CDC* pDC, const CRect* pRect = NULL, BOOL transparent = FALSE)
{
ASSERT(pDC != NULL); m_pDC = pDC;
m_pOldBitmap = NULL;
m_bMemDC = !pDC->IsPrinting(); // get the rectangle to draw
if (pRect == NULL)
{
pDC->GetClipBox(&m_rect);
}
else
{
m_rect = *pRect;
}
BOOL bRight = TRUE;
if (m_bMemDC)
{
// create a memory DC
CreateCompatibleDC(pDC);
pDC->LPtoDP(&m_rect); bRight = m_bitmap.CreateCompatibleBitmap(pDC, m_rect.Width(), m_rect.Height()); if (bRight)
{
m_pOldBitmap = SelectObject(&m_bitmap); SetMapMode(pDC->GetMapMode());
pDC->DPtoLP(&m_rect);
SetWindowOrg(m_rect.left, m_rect.top);
}
else
{
int iCount = 0;
}
}
else
{
// make a copy of the relevent parts of the current DC for printing
m_bPrinting = pDC->m_bPrinting;
m_hDC = pDC->m_hDC;
m_hAttribDC = pDC->m_hAttribDC;
} SetBkMode(TRANSPARENT); // fill background
if (transparent)
{
BitBlt(m_rect.left, m_rect.top, m_rect.Width(), m_rect.Height(), m_pDC, 0, 0, SRCCOPY);
}
else
{
FillSolidRect(m_rect, pDC->GetBkColor()); // not needed in OPAQUE mode?
}
} ~CMemDCEx()
{
if (m_bMemDC)
{
// copy the offscreen bitmap onto the screen
m_pDC->BitBlt(m_rect.left, m_rect.top, m_rect.Width(), m_rect.Height(),
this, m_rect.left, m_rect.top, SRCCOPY); // swap back the original bitmap
SelectObject(m_pOldBitmap);
}
else
{
// all we need to do is replace the DC with an illegal value, this keeps us from accidently
// deleting the handles associated with the CDC that was passed to the constructor
m_hDC = m_hAttribDC = NULL;
}
}private:
CBitmap m_bitmap; // offscreen bitmap
CBitmap* m_pOldBitmap; // bitmap originally found in CMemDCEx
CDC* m_pDC; // saves CDC passed in constructor
CRect m_rect; // rectangle of drawing area
BOOL m_bMemDC; // TRUE if CDC really is a Memory DC
};
{
public:
CMemDCEx(CDC* pDC, const CRect* pRect = NULL, BOOL transparent = FALSE)
{
ASSERT(pDC != NULL); m_pDC = pDC;
m_pOldBitmap = NULL;
m_bMemDC = !pDC->IsPrinting(); // get the rectangle to draw
if (pRect == NULL)
{
pDC->GetClipBox(&m_rect);
}
else
{
m_rect = *pRect;
}
BOOL bRight = TRUE;
if (m_bMemDC)
{
// create a memory DC
CreateCompatibleDC(pDC);
pDC->LPtoDP(&m_rect); bRight = m_bitmap.CreateCompatibleBitmap(pDC, m_rect.Width(), m_rect.Height()); if (bRight)
{
m_pOldBitmap = SelectObject(&m_bitmap); SetMapMode(pDC->GetMapMode());
pDC->DPtoLP(&m_rect);
SetWindowOrg(m_rect.left, m_rect.top);
}
else
{
int iCount = 0;
}
}
else
{
// make a copy of the relevent parts of the current DC for printing
m_bPrinting = pDC->m_bPrinting;
m_hDC = pDC->m_hDC;
m_hAttribDC = pDC->m_hAttribDC;
} SetBkMode(TRANSPARENT); // fill background
if (transparent)
{
BitBlt(m_rect.left, m_rect.top, m_rect.Width(), m_rect.Height(), m_pDC, 0, 0, SRCCOPY);
}
else
{
FillSolidRect(m_rect, pDC->GetBkColor()); // not needed in OPAQUE mode?
}
} ~CMemDCEx()
{
if (m_bMemDC)
{
// copy the offscreen bitmap onto the screen
m_pDC->BitBlt(m_rect.left, m_rect.top, m_rect.Width(), m_rect.Height(),
this, m_rect.left, m_rect.top, SRCCOPY); // swap back the original bitmap
SelectObject(m_pOldBitmap);
}
else
{
// all we need to do is replace the DC with an illegal value, this keeps us from accidently
// deleting the handles associated with the CDC that was passed to the constructor
m_hDC = m_hAttribDC = NULL;
}
}private:
CBitmap m_bitmap; // offscreen bitmap
CBitmap* m_pOldBitmap; // bitmap originally found in CMemDCEx
CDC* m_pDC; // saves CDC passed in constructor
CRect m_rect; // rectangle of drawing area
BOOL m_bMemDC; // TRUE if CDC really is a Memory DC
};
可是多次调用后,会在
bRight = m_bitmap.CreateCompatibleBitmap(pDC, m_rect.Width(), m_rect.Height());
bRight = false 了。
bRight是调试时添加的变量。我想确认下为什么会出现false这种情况。如何解决掉?
是不是使用SelectObject()有问题,需要做其它操作?
#define AFX_MEMDC_H__CA1D3541_7235_11D1_ABBA_00A0243D1382__INCLUDED_#if _MSC_VER >= 1000
#pragma once
#endif // _MSC_VER >= 1000
// MemDC.h : header file
////////////////////////////////////////////////////
// CMemDC - memory DC
//
// Author: Keith Rule
// Email: [email protected]
// Copyright 1996-1997, Keith Rule
//
// You may freely use or modify this code provided this
// Copyright is included in all derived versions.
//
// History - 10/3/97 Fixed scrolling bug.
// Added print support.
// 25 feb 98 - fixed minor assertion bug
//
// This class implements a memory Device Contextclass CMemDC : public CDC
{
public: // constructor sets up the memory DC
CMemDC(CDC* pDC) : CDC()
{
ASSERT(pDC != NULL); m_pDC = pDC;
m_pOldBitmap = NULL;
#ifndef _WIN32_WCE_NO_PRINTING
m_bMemDC = !pDC->IsPrinting();
#else
m_bMemDC = FALSE;
#endif if (m_bMemDC) // Create a Memory DC
{
pDC->GetClipBox(&m_rect);
CreateCompatibleDC(pDC);
m_bitmap.CreateCompatibleBitmap(pDC, m_rect.Width(), m_rect.Height());
m_pOldBitmap = SelectObject(&m_bitmap);
#ifndef _WIN32_WCE
SetWindowOrg(m_rect.left, m_rect.top);
#endif
// EFW - Bug fix - Fill background in case the user has overridden
// WM_ERASEBKGND. We end up with garbage otherwise.
// CJM - moved to fix a bug in the fix.
FillSolidRect(m_rect, pDC->GetBkColor());
}
else // Make a copy of the relevent parts of the current DC for printing
{
#if !defined(_WIN32_WCE) || ((_WIN32_WCE > 201) && !defined(_WIN32_WCE_NO_PRINTING))
m_bPrinting = pDC->m_bPrinting;
#endif
m_hDC = pDC->m_hDC;
m_hAttribDC = pDC->m_hAttribDC;
} } // Destructor copies the contents of the mem DC to the original DC
~CMemDC()
{
if (m_bMemDC)
{
// Copy the offscreen bitmap onto the screen.
m_pDC->BitBlt(m_rect.left, m_rect.top, m_rect.Width(), m_rect.Height(),
this, m_rect.left, m_rect.top, SRCCOPY); //Swap back the original bitmap.
SelectObject(m_pOldBitmap);
} else {
// All we need to do is replace the DC with an illegal value,
// this keeps us from accidently deleting the handles associated with
// the CDC that was passed to the constructor.
m_hDC = m_hAttribDC = NULL;
}
} // Allow usage as a pointer
CMemDC* operator->() {return this;}
// Allow usage as a pointer
operator CMemDC*() {return this;}private:
CBitmap m_bitmap; // Offscreen bitmap
CBitmap* m_pOldBitmap; // bitmap originally found in CMemDC
CDC* m_pDC; // Saves CDC passed in constructor
CRect m_rect; // Rectangle of drawing area.
BOOL m_bMemDC; // TRUE if CDC really is a Memory DC.
};///////////////////////////////////////////////////////////////////////////////{{AFX_INSERT_LOCATION}}
// Microsoft Developer Studio will insert additional declarations immediately before the previous line.#endif // !defined(AFX_MEMDC_H__CA1D3541_7235_11D1_ABBA_00A0243D1382__INCLUDED_)你比较比较看看
1.DeleteObject的使用
2.注意ReleaseDC和DeleteDC的使用
是上层的问题。上层在构造里使用了new,在析构使用的del,可是一直没有调用析构才导致程序挂掉。