Problem with line alignment for Bitmap data

[vanselm]

Hello,

I have already searched on the Internet about how to align each line of the bitmap data, so that it is displayed correctly. The lines must be a multiple of 4 Byte. I also tried to do so, however the problem still exists. As long as the image width is a multiple of 4 Byte, then it is displayed correctly otherwise, the lines are shifted against each other, so that the image is displayed corruptly ( see the attached files).

my steps to display the image are:

1) Load the image from the .bmp file

2) get its bits

3) Create and modify the BITMAPINFO struct, in order to pass it to SetStretchBltMode

4) display the image with "SetStretchBltMode"

// Enable button 'Load Image'
	GetDlgItem(IDC_BUTTON_LOAD_IMAGE)->EnableWindow(FALSE);

	CFileDialog dlg(TRUE, NULL, NULL, OFN_HIDEREADONLY|OFN_OVERWRITEPROMPT, _T("BMP Windows Bitmap|*.bmp|PNG Portable Network Graphics|*.png"));
	dlg.m_ofn.nFilterIndex = 1;
	dlg.m_ofn.lpstrTitle = _T("Search Test Image");
	if(dlg.DoModal() == IDOK)
	{
		m_strFileName = dlg.GetPathName();
		UpdateData(FALSE);

		HBITMAP hBitMap = (HBITMAP)LoadImage(NULL, m_strFileName,IMAGE_BITMAP, 0, 0, LR_LOADFROMFILE | LR_CREATEDIBSECTION | LR_DEFAULTSIZE);

		if (NULL != hBitMap)
		{
		
			CBitmap bmp;
			bmp.Attach((HBITMAP)hBitMap); // handle you got from LoadBitmap

			BITMAP bitmap;
			bmp.GetBitmap(&bitmap);

			int paddedRow = TJPAD(bitmap.bmWidth*bitmap.bmBitsPixel/8);
			unsigned long bufferSize = bitmap.bmHeight*paddedRow;
			if (NULL != m_bufferBeforeCompression)
			{
				delete[] m_bufferBeforeCompression;
				m_bufferBeforeCompression = NULL;
			}
			m_bufferBeforeCompression =  new unsigned char[bufferSize];

			//::GetBitmapBits((HBITMAP)hBitMap,bufferSize,m_bufferBeforeCompression );

			bmp.GetBitmapBits(bufferSize,m_bufferBeforeCompression );

			//  m_bufferBeforeCompression  is the pointer to the raw image data 

			m_nSizeX = bitmap.bmWidth;
			m_nSizeY = bitmap.bmHeight;
			m_nBitsPerPixel = bitmap.bmBitsPixel;

			// if it is a grayscale image, then only the grayscale subsampling for compression is possible
			if (m_nBitsPerPixel == 8)
			{
				m_cbSubsampling.SetCurSel(3);
			}

			display_frame(m_bufferBeforeCompression);
...

and here is the function which displays the image data:

void CVITA_MFCDlg::display_frame(unsigned char * ImageData)
{
	// get the device handle of the picture control
	CDC* pdc = GetDlgItem(IDC_DISPLAY_TEST)->GetDC();
	HDC hdc = pdc->m_hDC;

	// get the dimensions of the device window
	RECT rcClient;
	GetDlgItem(IDC_DISPLAY_TEST)->GetClientRect((LPRECT)&rcClient);
	INT picCtrlWidth = rcClient.right;
	INT picCtrlHeight = rcClient.bottom;


	BITMAPINFO* BmInfo;
	if (m_nBitsPerPixel == 8)
	{
		BmInfo = (BITMAPINFO*)alloca( sizeof(BITMAPINFOHEADER) + sizeof(RGBQUAD)*256);
		for(int i=0; i<256; i++)
		{
			BmInfo->bmiColors[i].rgbRed = i;
			BmInfo->bmiColors[i].rgbGreen = i;
			BmInfo->bmiColors[i].rgbBlue = i;
			BmInfo->bmiColors[i].rgbReserved = 0;
		}
	}
	else
	{
		BmInfo = (BITMAPINFO*)alloca( sizeof(BITMAPINFO));
	}

	BmInfo->bmiHeader.biSize		  = sizeof (BmInfo->bmiHeader);
	BmInfo->bmiHeader.biWidth		  = m_nSizeX;
	BmInfo->bmiHeader.biHeight		  = -m_nSizeY;
	BmInfo->bmiHeader.biPlanes		  = 1;
	BmInfo->bmiHeader.biBitCount	  = m_nBitsPerPixel;
	BmInfo->bmiHeader.biCompression	  = BI_RGB;
	//BmInfo->bmiHeader.biSizeImage	  = ((m_nSizeX * m_nBitsPerPixel +31) & ~31) /8 * m_nSizeY;
	BmInfo->bmiHeader.biSizeImage	  = m_nSizeY * TJPAD(m_nSizeX*m_nBitsPerPixel/8);
	BmInfo->bmiHeader.biClrUsed		  = 0;
	BmInfo->bmiHeader.biClrImportant  = 0;



	// use HALFTONE or MAXSTRETCHBLTMODE stretch mode, otherwise there are some artifacts within the image
	SetStretchBltMode(hdc,HALFTONE); 

	// display the content of the array on an output device and stretch the image accordingly to the device window dimensions
	::StretchDIBits(		hdc, 					// hDC
								0,						// DestX
								0,						// DestY
								picCtrlWidth,			// nDestWidth
								picCtrlHeight,			// nDestHeight
								0,						// SrcX
								0,						// SrcY
								m_nSizeX,				// SrcWidth
								m_nSizeY,				// SrcHeight
								(LPVOID)((LPDWORD)ImageData),		// lpBits
								(LPBITMAPINFO)BmInfo, 	// lpBitsInfo
								DIB_RGB_COLORS,			// wUsage
								SRCCOPY);				// wDwRop
	




	// make the device context free for application
	ReleaseDC(pdc);
}

#define TJPAD(p) (((p)+3)&(~3))

Could you please take a look at my code and tell me what I have to change in order to avoid the strange display bahaviour. Thanks.

best regards