JuniorHighClient/HJHomework/CacheDC.cpp

// CacheDC.cpp : 实现文件
//

#include "stdafx.h"
#include "HJHomework.h"
#include "CacheDC.h"


// CCacheDC

CCacheDC::CCacheDC(CDC *pDC,CRect rect/* = CRect(0, 0, 0, 0)*/, BOOL bCopyFirst/* = TRUE*/)
	:CDC(), m_oldBitmap(NULL), m_pDC(pDC)
{

	ASSERT(m_pDC != NULL);			// 断言参数不为空

	m_bMemDC = !pDC->IsPrinting();	// 判断设备是否用于打印

	if (m_bMemDC)
	{
		CreateCompatibleDC(pDC);										//	创建一个内存DC
		if (rect == CRect(0, 0, 0, 0))									//	判断绘画区域
		{
			pDC->GetClipBox(&m_rect);									//	得到一个能够完整包含当前可见区域的最小矩形的大小
		}else
		{
			m_rect = rect;
		}

		//创建兼容位图
		m_bitmap.CreateCompatibleBitmap(pDC, m_rect.Width(), m_rect.Height());
		m_oldBitmap = SelectObject(&m_bitmap);							//	保留旧位图对象
		SetWindowOrg(m_rect.left, m_rect.top);							//	移动窗口原点
		if (bCopyFirst)													//	初次复制
		{
			this->BitBlt(m_rect.left, m_rect.top, m_rect.Width(), m_rect.Height(), m_pDC, m_rect.left, m_rect.top, SRCCOPY);
		}
	}
	else
	{
		//创建一个跟当前DC绘制有关的副本
		m_bPrinting = pDC->m_bPrinting;
		m_hDC = pDC->m_hDC;
		m_hAttribDC = pDC->m_hAttribDC;
	}
}

CCacheDC::~CCacheDC()
{
	if (m_bMemDC)
	{
		//	复制屏幕外位图到屏幕内
		m_pDC->BitBlt(m_rect.left, m_rect.top, m_rect.Width(), m_rect.Height(), this, m_rect.left, m_rect.top, SRCCOPY);
		SelectObject(m_oldBitmap);						//交换原来的位图
	}else
	{
		m_hDC = m_hAttribDC = NULL;
	}
}