在许多资料上都说CImage类是基于GDI+的，但是为什么是基于GDI+的呢？

     因为使用这个类时，并没有加入#include <gdiplus.h> ，也没有在程序开始和结束时分别写GDI+启动代码GdiplusStartupInput和结束代码GdiplusShutdown

使用这个类时，仅仅需要添加头文件# include<altimage.h>就可以了，比GDI+得使用要简单一些。

     而CImage 对图片的处理很类似GDI+ ，其内部是不是封装了GDI+呢？ 幸好，CImage类 是源码公开的，我们可以研究其源码，以便加深理解。

    首先，看看altimage.h头文件

#ifndef __ATLIMAGE_H__#define __ATLIMAGE_H__#pragma once#include <atldef.h>#include <atlbase.h>#include <atlstr.h>#include <atlsimpcoll.h>#include <atltypes.h>#ifndef _ATL_NO_PRAGMA_WARNINGS#pragma warning (push)#pragma warning(disable : 4820) // padding added after member#endif //!_ATL_NO_PRAGMA_WARNINGS#pragma warning( push, 3 )#pragma push_macro(“new”)#undef new#include <gdiplus.h> // 注意这里：添加了GDI+得头文件#pragma pop_macro(“new”)#pragma warning( pop )#include <shlwapi.h>#ifndef _ATL_NO_DEFAULT_LIBS#pragma comment(lib, “gdi32.lib”)#pragma comment(lib, “shlwapi.lib”)#pragma comment(lib, “gdiplus.lib”)#if WINVER >= 0x0500#pragma comment(lib, “msimg32.lib”)#endif // WINVER >= 0x0500#endif // !_ATL_NO_DEFAULT_LIBS#pragma pack(push, _ATL_PACKING)

上面包含了GDI+得头文件

再来看CImage的定义：

class CImage{private: class CDCCache { public: CDCCache() throw(); ~CDCCache() throw(); HDC GetDC() throw(); void ReleaseDC( HDC ) throw(); private: HDC m_ahDCs[CIMAGE_DC_CACHE_SIZE]; }; class CInitGDIPlus { public: CInitGDIPlus() throw(); ~CInitGDIPlus() throw(); bool Init() throw(); void ReleaseGDIPlus() throw(); void IncreaseCImageCount() throw(); void DecreaseCImageCount() throw(); private: ULONG_PTR m_dwToken; CRITICAL_SECTION m_sect; LONG m_nCImageObjects; };

static CInitGDIPlus s_initGDIPlus;

static CDCCache s_cache;

它定义了两个类成员变量： 其中CInitGDIPlus 是负责GDI+的启动和释放

我们再看一下，这个成员类的Init()方法：

inline bool CImage::CInitGDIPlus::Init() throw(){ EnterCriticalSection(&m_sect); bool fRet = true; if( m_dwToken == 0 ) { Gdiplus::GdiplusStartupInput input; Gdiplus::GdiplusStartupOutput output; Gdiplus::Status status = Gdiplus::GdiplusStartup( &m_dwToken, &input, &output ); //启动GDI+ if( status != Gdiplus::Ok ) fRet = false; } LeaveCriticalSection(&m_sect); return fRet;}

也就是说 使用这个函数 启动GDI+

再看下一个函数：

inline void CImage::CInitGDIPlus::ReleaseGDIPlus() throw(){ EnterCriticalSection(&m_sect); if( m_dwToken != 0 ) { Gdiplus::GdiplusShutdown( m_dwToken ); } m_dwToken = 0; LeaveCriticalSection(&m_sect);}

也就是说， 使用这一个函数，用来关闭GDI+

到此，我们便可知道，CImage类是基于GDI+的，但是我们还不知道CImage 对象是不是在初始化时就启动了GDI+？如果不是，那什么时候才启动GDI+呢？

为解决这个疑惑，我们查看CImage 构造函数

inline CImage::CImage() throw() : m_hBitmap( NULL ), m_pBits( NULL ), m_hDC( NULL ), m_nDCRefCount( 0 ), m_hOldBitmap( NULL ), m_nWidth( 0 ), m_nHeight( 0 ), m_nPitch( 0 ), m_nBPP( 0 ), m_iTransparentColor( -1 ), m_bHasAlphaChannel( false ), m_bIsDIBSection( false ){ s_initGDIPlus.IncreaseCImageCount();}

inline void CImage::CInitGDIPlus::IncreaseCImageCount() throw(){ EnterCriticalSection(&m_sect); m_nCImageObjects++; LeaveCriticalSection(&m_sect);}

由此可见，构造函数并没有启动GDI+

也就是说定义  CImage image;  这个image变量时，并没有启动GDI+

我们继续查找：

inline bool CImage::InitGDIPlus() throw(){ bool bSuccess = s_initGDIPlus.Init(); return( bSuccess );}

CImage使用InitGDIPlus（） 来初始化GDI+

因此我们查找InitGDIPlus() 的所有引用 ，发现以下函数：

inline HRESULT CImage::GetImporterFilterString( CSimpleString& strImporters, CSimpleArray< GUID >& aguidFileTypes, LPCTSTR pszAllFilesDescription /* = NULL */, DWORD dwExclude /* = excludeDefaultLoad */, TCHAR chSeparator /* = \’|\’ */ ){ if( !InitGDIPlus() ) { return( E_FAIL ); } UINT nCodecs; UINT nSize; Gdiplus::Status status; Gdiplus::ImageCodecInfo* pCodecs; status = Gdiplus::GetImageDecodersSize( &nCodecs, &nSize ); USES_ATL_SAFE_ALLOCA; pCodecs = static_cast< Gdiplus::ImageCodecInfo* >( _ATL_SAFE_ALLOCA(nSize, _ATL_SAFE_ALLOCA_DEF_THRESHOLD) ); if( pCodecs == NULL ) return E_OUTOFMEMORY; status = Gdiplus::GetImageDecoders( nCodecs, nSize, pCodecs ); BuildCodecFilterString( pCodecs, nCodecs, strImporters, aguidFileTypes, pszAllFilesDescription, dwExclude, chSeparator ); return( S_OK );}inline HRESULT CImage::GetExporterFilterString( CSimpleString& strExporters, CSimpleArray< GUID >& aguidFileTypes, LPCTSTR pszAllFilesDescription /* = NULL */, DWORD dwExclude /* = excludeDefaultSave */, TCHAR chSeparator /* = \’|\’ */ ){ if( !InitGDIPlus() ) { return( E_FAIL ); } UINT nCodecs; UINT nSize; Gdiplus::Status status; Gdiplus::ImageCodecInfo* pCodecs; status = Gdiplus::GetImageDecodersSize( &nCodecs, &nSize ); USES_ATL_SAFE_ALLOCA; pCodecs = static_cast< Gdiplus::ImageCodecInfo* >( _ATL_SAFE_ALLOCA(nSize, _ATL_SAFE_ALLOCA_DEF_THRESHOLD) ); if( pCodecs == NULL ) return E_OUTOFMEMORY; status = Gdiplus::GetImageDecoders( nCodecs, nSize, pCodecs ); BuildCodecFilterString( pCodecs, nCodecs, strExporters, aguidFileTypes, pszAllFilesDescription, dwExclude, chSeparator ); return( S_OK );}

inline HRESULT CImage::Load( IStream* pStream ) throw(){ if( !InitGDIPlus() ) { return( E_FAIL ); } Gdiplus::Bitmap bmSrc( pStream ); if( bmSrc.GetLastStatus() != Gdiplus::Ok ) { return( E_FAIL ); } return( CreateFromGdiplusBitmap( bmSrc ) );}inline HRESULT CImage::Load( LPCTSTR pszFileName ) throw(){ if( !InitGDIPlus() ) { return( E_FAIL ); } Gdiplus::Bitmap bmSrc( (CT2W)pszFileName ); if( bmSrc.GetLastStatus() != Gdiplus::Ok ) { return( E_FAIL ); } return( CreateFromGdiplusBitmap( bmSrc ) );}

inline HRESULT CImage::Save( IStream* pStream, REFGUID guidFileType ) const throw(){ if( !InitGDIPlus() ) { return( E_FAIL ); } UINT nEncoders; UINT nBytes; Gdiplus::Status status; status = Gdiplus::GetImageEncodersSize( &nEncoders, &nBytes ); if( status != Gdiplus::Ok ) { return( E_FAIL ); } USES_ATL_SAFE_ALLOCA; Gdiplus::ImageCodecInfo* pEncoders = static_cast< Gdiplus::ImageCodecInfo* >( _ATL_SAFE_ALLOCA(nBytes, _ATL_SAFE_ALLOCA_DEF_THRESHOLD) ); if( pEncoders == NULL ) return E_OUTOFMEMORY; status = Gdiplus::GetImageEncoders( nEncoders, nBytes, pEncoders ); if( status != Gdiplus::Ok ) { return( E_FAIL ); } CLSID clsidEncoder = FindCodecForFileType( guidFileType, pEncoders, nEncoders ); if( clsidEncoder == CLSID_NULL ) { return( E_FAIL ); } if( m_bHasAlphaChannel ) { ATLASSUME( m_nBPP == 32 ); Gdiplus::Bitmap bm( m_nWidth, m_nHeight, m_nPitch, PixelFormat32bppARGB, static_cast< BYTE* >( m_pBits ) ); status = bm.Save( pStream, &clsidEncoder, NULL ); if( status != Gdiplus::Ok ) { return( E_FAIL ); } } else { Gdiplus::Bitmap bm( m_hBitmap, NULL ); status = bm.Save( pStream, &clsidEncoder, NULL ); if( status != Gdiplus::Ok ) { return( E_FAIL ); } } return( S_OK );}inline HRESULT CImage::Save( LPCTSTR pszFileName, REFGUID guidFileType ) const throw(){ if( !InitGDIPlus() ) { return( E_FAIL ); } UINT nEncoders; UINT nBytes; Gdiplus::Status status; status = Gdiplus::GetImageEncodersSize( &nEncoders, &nBytes ); if( status != Gdiplus::Ok ) { return( E_FAIL ); } USES_CONVERSION_EX; Gdiplus::ImageCodecInfo* pEncoders = static_cast< Gdiplus::ImageCodecInfo* >( _ATL_SAFE_ALLOCA(nBytes, _ATL_SAFE_ALLOCA_DEF_THRESHOLD) ); if( pEncoders == NULL ) return E_OUTOFMEMORY; status = Gdiplus::GetImageEncoders( nEncoders, nBytes, pEncoders ); if( status != Gdiplus::Ok ) { return( E_FAIL ); } CLSID clsidEncoder = CLSID_NULL; if( guidFileType == GUID_NULL ) { // Determine clsid from extension clsidEncoder = FindCodecForExtension( ::PathFindExtension( pszFileName ), pEncoders, nEncoders ); } else { // Determine clsid from file type clsidEncoder = FindCodecForFileType( guidFileType, pEncoders, nEncoders ); } if( clsidEncoder == CLSID_NULL ) { return( E_FAIL ); } LPCWSTR pwszFileName = T2CW_EX( pszFileName, _ATL_SAFE_ALLOCA_DEF_THRESHOLD );#ifndef _UNICODE if( pwszFileName == NULL ) return E_OUTOFMEMORY;#endif // _UNICODE if( m_bHasAlphaChannel ) { ATLASSUME( m_nBPP == 32 ); Gdiplus::Bitmap bm( m_nWidth, m_nHeight, m_nPitch, PixelFormat32bppARGB, static_cast< BYTE* >( m_pBits ) ); status = bm.Save( pwszFileName, &clsidEncoder, NULL ); if( status != Gdiplus::Ok ) { return( E_FAIL ); } } else { Gdiplus::Bitmap bm( m_hBitmap, NULL ); status = bm.Save( pwszFileName, &clsidEncoder, NULL ); if( status != Gdiplus::Ok ) { return( E_FAIL ); } } return( S_OK );}

有上面可知： CImage对象 在第一次Load() 或第一次Save() 时 启动GDI+

下面我们看看 CImage析构时，是否能将GDI+关闭掉：

inline CImage::~CImage() throw(){ Destroy(); s_initGDIPlus.DecreaseCImageCount();}

inline void CImage::CInitGDIPlus::DecreaseCImageCount() throw(){ EnterCriticalSection(&m_sect); if( –m_nCImageObjects == 0 ) ReleaseGDIPlus(); LeaveCriticalSection(&m_sect);}

inline void CImage::CInitGDIPlus::ReleaseGDIPlus() throw(){ EnterCriticalSection(&m_sect); if( m_dwToken != 0 ) { Gdiplus::GdiplusShutdown( m_dwToken ); } m_dwToken = 0; LeaveCriticalSection(&m_sect);}

也就是说，一个CImage对象退出时，并不直接关闭GDI+ ，而是仅仅将GDI+使用计数减一， 当其为0时，再关闭GDI+

而这是通过类静态变量来实现计数的：

static CInitGDIPlus s_initGDIPlus;

由此，我们可作如下总结：

      当定义多个CImge 变量时， 当某个变量加载图片或保存图片时，启动GDI+，之后， 当其他变量再加载图片或保存时，增加GDI+计数变量

      当所有CImage变量都析构完毕时，才关闭GDI+，否则，只是减少GDI+计算变量值。

      所以说，CImage类是基于GDI+的。

原文地址：http://blog.csdn.net/shuilan0066/article/details/7086371 

我不喜欢做界面，所以就看过一次，因为我不会，所以有个印象。

CImage 是 GDI+ 里的东西