DIB (device independent bitmap) combined with HDC (device context)

dib32.cpp

#include <windows.h>

class dib32
  {
    const unsigned _width;
    const unsigned _height;
    void*      _bits;
    mutable HBITMAP    _old_bitmap;
    mutable HDC        _dc;
    HBITMAP    _bitmap;

    BITMAPINFO _bitmap_info;

  public:

    dib32(unsigned w, unsigned h) :
      _width(w),
      _height(h),
      _bits(0),
      _old_bitmap(0),
      _dc(0) {

      memset(&_bitmap_info,0,sizeof(_bitmap_info));
      _bitmap_info.bmiHeader.biSize = sizeof(_bitmap_info.bmiHeader);
      _bitmap_info.bmiHeader.biWidth = _width;
      _bitmap_info.bmiHeader.biHeight = 0 - int(_height);
      _bitmap_info.bmiHeader.biPlanes = 1;
      _bitmap_info.bmiHeader.biBitCount = 32;
      _bitmap_info.bmiHeader.biCompression = BI_RGB;

      _bitmap = ::CreateDIBSection(
            NULL, // device context
            &_bitmap_info,
            DIB_RGB_COLORS,
            &_bits,
            0, // file mapping object
            0); // file offset

      if (0 == _bits) {
        return;
        //throw std::bad_alloc();
      }

      memset(_bits,0, _width * _height * 4);

    }

    ~dib32() {
      if( _dc )
      {
        ::SelectObject(_dc,_old_bitmap);
        ::DeleteDC(_dc);
      }
      if( _bitmap )
        ::DeleteObject(_bitmap);
    }

    void set_white()
    {
      memset(_bits,0xff, _width * _height * 4);
    }

    unsigned  width() const { return _width; }
    unsigned  height() const { return _height; }
    void* bits() const { return _bits; }
    BYTE* bytes() const { return (BYTE*)_bits; }
    HDC   DC() const 
    { 
      if(!_dc) {
        _dc = ::CreateCompatibleDC(NULL);
        if (_dc)
          _old_bitmap = (HBITMAP)::SelectObject(_dc,_bitmap);
      }
      return _dc; 
    }

    HBITMAP   detach() { auto r = _bitmap; _bitmap = 0; return r; }

    const BITMAPINFO& get_info() const { return _bitmap_info; }
  };