CMemDC 源码

//////////////////////////////////////////////////// CMemDC - memory DC//// Author: Keith Rule// Email: [e-mail]// Copyright 1996-1999, 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. - KR//// 11/3/99 Fixed most common complaint. Added// background color fill. - KR//// 11/3/99 Added support for mapping modes other than// MM_TEXT as suggested by Lee Sang Hun. - KR//// This class implements a memory Device Context which allows// flicker free drawing.class CMemDC : public CDC {private: CBitmap m_bitmap; // Offscreen bitmap CBitmap* m_oldBitmap; // 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.public: CMemDC(CDC* pDC, const CRect* pRect = NULL) : CDC() { ASSERT(pDC != NULL); // Some initialization m_pDC = pDC; m_oldBitmap = NULL; m_bMemDC = !pDC->IsPrinting(); // Get the rectangle to draw if (pRect == NULL) { pDC->GetClipBox(&m_rect); } else { m_rect = *pRect; } if (m_bMemDC) { // Create a Memory DC CreateCompatibleDC(pDC); pDC->LPtoDP(&m_rect); m_bitmap.CreateCompatibleBitmap(pDC, m_rect.Width(), m_rect.Height()); m_oldBitmap = SelectObject(&m_bitmap); SetMapMode(pDC->GetMapMode()); pDC->DPtoLP(&m_rect); SetWindowOrg(m_rect.left, m_rect.top); } 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; } // Fill background FillSolidRect(m_rect, pDC->GetBkColor()); } ~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_oldBitmap); } 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; }};