VC++中图像处理类CBitmap的用法

前端技术 2023/09/09 C++

VC++中图像处理类CBitmap的用法

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

复制代码 代码如下:
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();
}

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