bvCreateDcForStretchBlt

This helper function creates a device context for bitmap stretching.

Return value: a handle of device context.

Notes:

This function is used to fix a strange bug which happens sometimes with printer's device context. Let us imagine a situation when we want to draw a bitmap on the printer using StretchBlt() function:

		HDC dc; // printer's device context, has been initialized somewhere
		int ires(0);
		HDC dc2=::CreateCompatibleDC(dc);
		HBITMAP hOldBitmap=(HBITMAP) ::SelectObject(dc2,m_hBitmap);
		ires=::StretchBlt(dc,x,y,w,h,dc2,0,0,BitmapDesc.bmWidth,BitmapDesc.bmHeight,SRCCOPY);
		::SelectObject(dc2,hOldBitmap);
		::DeleteDC(dc2);
		

The idea is clear, this is the standart way to stretch bitmaps in MS Windows. But the problem is that, on some printers, this code does not work. ires is OK but there is no bitmap on the paper. Hovewer, if we change the code in the next way:

		HDC dc; // printer's device context, has been initialized somewhere
		int ires(0);		
		HDC _dc2=::CreateDC(_T("DISPLAY"),0,0,0);
		HDC dc2=::CreateCompatibleDC(_dc2);
		::DeleteDC(_dc2);
		HBITMAP hOldBitmap=(HBITMAP) ::SelectObject(dc2,m_hBitmap);
		ires=::StretchBlt(dc,x,y,w,h,dc2,0,0,BitmapDesc.bmWidth,BitmapDesc.bmHeight,SRCCOPY);
		::SelectObject(dc2,hOldBitmap);
		::DeleteDC(dc2);		
			

it works very well. Here the display HDC is used as temporary. So, to not to write such code every time this function was written. Below is the source code of the bvCreateDcForStretchBlt() function:

		BESTVIEWAPI(HDC) bvCreateDcForStretchBlt()
			{
			HDC _dc=CreateDC(_T("DISPLAY"),0,0,0);
			HDC dc=CreateCompatibleDC(_dc);
			DeleteDC(_dc);	
			return dc;
			}