MFC 双缓冲实现
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#pragma once
//用这个类可以实现双缓冲
/*
通过
CMemoryDC dc(pDc); 创建一个内存DC,
dc.Fill(); 全部是内存Bitmap上画图
当dc析构时,将内存bitmap直接拷贝到物理DC上去.
*/
class CMemoryDC
:public CDC
{
protected:
CBitmap m_bitmap; // Offscreen bitmap 内存的位图
CBitmap* m_oldBitmap; // bitmap originally found in CMemDC 原始位图
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.
void Construct(CDC* pDC)
{
ASSERT(pDC != NULL);
// Some initialization
m_pDC = pDC;
m_oldBitmap = NULL;
m_bMemDC = !pDC->IsPrinting();
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());
}
// TRK begin
public:
CMemoryDC(CDC* pDC ) : CDC() { pDC->GetClipBox(&m_rect); Construct(pDC); }
CMemoryDC(CDC* pDC, const RECT& rect) : CDC() { m_rect = rect ; Construct(pDC); }
// TRK end
virtual ~CMemoryDC()
{
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
CMemoryDC* operator->()
{
return this;
}
// Allow usage as a pointer
operator CMemoryDC*()
{
return this;
}
};
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