VC++ GDI 总结 一一 CBitmap类

class CBitmap : public CGdiObject
{
    DECLARE_DYNAMIC(CBitmap)

public:
    static CBitmap* PASCAL FromHandle(HBITMAP hBitmap);

// Constructors
    CBitmap();

    BOOL LoadBitmap(LPCTSTR lpszResourceName);
    BOOL LoadBitmap(UINT nIDResource);
    BOOL LoadOEMBitmap(UINT nIDBitmap); // for OBM_/OCR_/OIC_
#ifndef _AFX_NO_AFXCMN_SUPPORT
    BOOL LoadMappedBitmap(UINT nIDBitmap, UINT nFlags = 0,
        LPCOLORMAP lpColorMap = NULL, int nMapSize = 0);
#endif
    BOOL CreateBitmap(int nWidth, int nHeight, UINT nPlanes, UINT nBitcount,
            const void* lpBits);
    BOOL CreateBitmapIndirect(LPBITMAP lpBitmap);
    BOOL CreateCompatibleBitmap(CDC* pDC, int nWidth, int nHeight);
    BOOL CreateDiscardableBitmap(CDC* pDC, int nWidth, int nHeight);

// Attributes
    operator HBITMAP() const;
    int GetBitmap(BITMAP* pBitMap);

// Operations
    DWORD SetBitmapBits(DWORD dwCount, const void* lpBits);
    DWORD GetBitmapBits(DWORD dwCount, LPVOID lpBits) const;
    CSize SetBitmapDimension(int nWidth, int nHeight);
    CSize GetBitmapDimension() const;

// Implementation
public:
    virtual ~CBitmap();
#ifdef _DEBUG
    virtual void Dump(CDumpContext& dc) const;
#endif
};

父

CGdiObject

class CGdiObject : public CObject
{
    DECLARE_DYNCREATE(CGdiObject)
public:

// Attributes
    HGDIOBJ m_hObject;                  // must be first data member
    operator HGDIOBJ() const;
    HGDIOBJ GetSafeHandle() const;

    static CGdiObject* PASCAL FromHandle(HGDIOBJ hObject);
    static void PASCAL DeleteTempMap();
    BOOL Attach(HGDIOBJ hObject);
    HGDIOBJ Detach();

// Constructors
    CGdiObject(); // must Create a derived class object
    BOOL DeleteObject();

// Operations
#pragma push_macro("GetObject")
#undef GetObject
    int _AFX_FUNCNAME(GetObject)(int nCount, LPVOID lpObject) const;
    int GetObject(int nCount, LPVOID lpObject) const;
#pragma pop_macro("GetObject")
    UINT GetObjectType() const;
    BOOL CreateStockObject(int nIndex);
    BOOL UnrealizeObject();
    BOOL operator==(const CGdiObject& obj) const;
    BOOL operator!=(const CGdiObject& obj) const;

// Implementation
public:
    virtual ~CGdiObject();
#ifdef _DEBUG
    virtual void Dump(CDumpContext& dc) const;
    virtual void AssertValid() const;
#endif
};

1 装载已导入工程的位图资源

// 装载位图

    CBitmap bmp;
    bmp.LoadBitmap(IDB_BITMAP);

2 装载位图文件

    为了能让CBitmap能够装载位图文件，必须调用API函数LoadImage

HANDLE LoadImage(
  HINSTANCE hinst,   // handle of the instance containing the image
  LPCTSTR lpszName,  // name or identifier of image
  UINT uType,        // type of image
  int cxDesired,     // desired width
  int cyDesired,     // desired height
  UINT fuLoad        // load flags
);

装载： Example 1:

HBITMAP hBmp = (HBITMAP)LoadImage(NULL,
        m_fileName,
        IMAGE_BITMAP, 
        0, 0, 
        LR_LOADFROMFILE | LR_DEFAULTCOLOR | LR_DEFAULTSIZE);

Example 2:

HBITMAP    hBmp = (HBITMAP)::LoadImage(AfxGetInstanceHandle(),
        "BG.bmp",
        IMAGE_BITMAP,
        0,0,
        LR_LOADFROMFILE);

将装载后得到的HBITMAP资源句柄 与 CBitmap 对象 相连

if (hBmp != NULL) {
        CBitmap *pBmp = CBitmap::FromHandle(hBmp);
    }

或

CBitmap bmp;
    if (hBmp != NULL) {
        bmp.DeleteObject();
        bmp.Attach(hBmp);    
    }

3 显示位图

CBitmap bmp;
    bmp.LoadBitmap(IDB_BITMAP1);
    
    BITMAP bm;
    bmp.GetBitmap(&bm);

    CDC dc;
    dc.CreateCompatibleDC(pDC);
    CBitmap*pOldBmp=(CBitmap *)dc.SelectObject(&bmp);

    pDC->BitBlt(0,0,bm.bmWidth,bm.bmHeight,&dc,0,0,SRCCOPY);
    pDC->SelectObject(pOldBmp);

    bmp.DeleteObject();
    bmp.LoadBitmap(IDB_BITMAP2);

4 删除资源

CBitmap bmp;
    bmp.LoadBitmap(IDB_BITMAP);

    CBitmap *pOld=pDC->SelectObject(&bmp);

    // 此时位图对象还在pDC中，因此不能马上删除
    // 而是先将位图从DC中选出 然后再删除
    pDC->SelectObject(pOld);
    bmp.DeleteObject();

5 CBitmap 析构

当CBitmap作为局部变量 在其退出作用范围后，会发生析构，这时候CBitmap会将其对应的位图资源（hBitmap ）释放掉。

若想继续使用该位图资源hBitmap，则在退出作用范围前，应将位图资源hBitmap和CBitmap对象通过Detach()函数进行分离

HBITMAP  CMyClass::Load()
{
    CBitmap bmp;
    bmp.LoadBitmap(IDB_BITMAP);

    // 通过Detach 将资源与对象分离，这样bmp析构后，资源仍存在  
    // 否则 ，bmp析构时，会将位图资源一起析构掉，这样出了局部范围外，就不可再使用这个位图资源了
    return bmp.Detach();
}

6 在仅获得HBITMAP资源句柄情况下，如何获得这个资源的BITMAP信息

BITMAP bm;
GetObject(hBitmap,sizeof(BITMAP),&bm);

7 在内存中开辟资源空间 将原图保存到内存中

//-------------------在内存中建立区域以存放所得位图-------------------
// hBitmapSrc 为 CBitmap中保存的矩形原图资源句柄
// hDC 句柄   
// 在内存中开辟位图资源，用以保存原图
HBITMAP CopyHBitmap(HBITMAP hBitmapSrc,HDC hDC)
{
    
    BITMAP bm;
    HBITMAP hBitmapDst;
    HDC hdcSrc,hdcDst;

    GetObject(hBitmapSrc,sizeof(BITMAP),&bm);
    hBitmapDst=CreateCompatibleBitmap(hDC,bm.bmWidth,bm.bmHeight);

    hdcSrc=CreateCompatibleDC(hDC);
    hdcDst=CreateCompatibleDC(hDC);

    SelectObject(hdcSrc,hBitmapSrc); 
    SelectObject(hdcDst,hBitmapDst);

    BitBlt(hdcDst,0,0,bm.bmWidth,bm.bmHeight,hdcSrc,0,0,SRCCOPY);
    
    DeleteDC(hdcSrc);
    DeleteDC(hdcDst);    
    return hBitmapDst;

}