GDI+ 總結二 ： 爲什麼說CImage類是基於GDI+的？

      在許多資料上都說CImage類是基於GDI+的，但是爲什麼是基於GDI+的呢？

 

     因爲使用這個類時，並沒有加入#include <gdiplus.h> ，也沒有在程序開始和結束時分別寫GDI+啓動代碼GdiplusStartupInput和結束代碼GdiplusShutdown

使用這個類時，僅僅需要添加頭文件# include<altimage.h>就可以了，比GDI+得使用要簡單一些。

 

     而CImage 對圖片的處理很類似GDI+ ，其內部是不是封裝了GDI+呢？ 幸好，CImage類 是源碼公開的，我們可以研究其源碼，以便加深理解。

 

    首先，看看altimage.h頭文件

#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>   // 注意這裏：添加了GDI+得頭文件
#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+得頭文件

 

再來看CImage的定義：

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;

它定義了兩個類成員變量： 其中CInitGDIPlus 是負責GDI+的啓動和釋放

 

我們再看一下，這個成員類的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 );   //啓動GDI+
        if( status != Gdiplus::Ok )
            fRet = false;
    }
    LeaveCriticalSection(&m_sect);
    return fRet;
}

也就是說 使用這個函數 啓動GDI+

 

再看下一個函數：

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

也就是說， 使用這一個函數，用來關閉GDI+

 

到此，我們便可知道，CImage類是基於GDI+的，但是我們還不知道CImage 對象是不是在初始化時就啓動了GDI+？如果不是，那什麼時候才啓動GDI+呢？

爲解決這個疑惑，我們查看CImage 構造函數

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);
}

由此可見，構造函數並沒有啓動GDI+

也就是說定義  CImage image;  這個image變量時，並沒有啓動GDI+

 

我們繼續查找：

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

CImage使用InitGDIPlus（） 來初始化GDI+

因此我們查找InitGDIPlus() 的所有引用 ，發現以下函數：

 

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對象 在第一次Load() 或第一次Save() 時 啓動GDI+

 

下面我們看看 CImage析構時，是否能將GDI+關閉掉：

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);
}

也就是說，一個CImage對象退出時，並不直接關閉GDI+ ，而是僅僅將GDI+使用計數減一， 當其爲0時，再關閉GDI+

而這是通過類靜態變量來實現計數的：

static CInitGDIPlus s_initGDIPlus;

 

由此，我們可作如下總結：

 

      當定義多個CImge 變量時， 當某個變量加載圖片或保存圖片時，啓動GDI+，之後， 當其他變量再加載圖片或保存時，增加GDI+計數變量

      當所有CImage變量都析構完畢時，才關閉GDI+，否則，只是減少GDI+計算變量值。

      所以說，CImage類是基於GDI+的。

 

 轉自：http://blog.csdn.net/shuilan0066/article/details/7086371