C / C++ / MFC

Richard MacCutchan11-Mar-20 8:44

11-Mar-20 8:44

fearless_ wrote:
Is there a way to work around the problem?

Yes, remove the duplicate include statement.

Calin Negru11-Mar-20 10:49

11-Mar-20 10:49

thanks, with a simple tweak at headers it worked

Calin Negru11-Mar-20 22:51

11-Mar-20 22:51

Would you mind helping me further? I loaded the bitmap, however when I check the values from the array into which the bitmap is loaded they show up as 0 (null).

modified 12-Mar-20 4:05am.

Richard MacCutchan11-Mar-20 23:35

11-Mar-20 23:35

Really. And we are supposed to guess what code and where the error occurs?

Calin Negru12-Mar-20 0:27

12-Mar-20 0:27

here is my code

StringCchPrintfA(pszFilename,1024,"hello.bmp");
	// Attempt to open the Dib file for reading.
	if( !cf.Open( pszFilename, CFile::modeRead ) )
	{
		StringCchPrintfA(message,1024,"error reading file");
		MessageBox(NULL, message, "Textures.exe", MB_OK);
		return( FALSE );
	}
		

	// Get the size of the file and store
	// in a local variable. Subtract the
	// size of the BITMAPFILEHEADER structure
	// since we won't keep that in memory.
	DWORD dwDibSize= cf.GetLength() - sizeof( BITMAPFILEHEADER );
	int bsize =0;
	//dwDibSize =
	bsize=	cf.GetLength() - sizeof( BITMAPFILEHEADER );
	StringCchPrintfA(message,1024,"bitmap size  %d",bsize);
	MessageBox(NULL, message, "Textures.exe", MB_OK);

	// Attempt to allocate the Dib memory.
	unsigned char *pDib;
	pDib = new unsigned char [dwDibSize];
	if( pDib == NULL )
	{
			StringCchPrintfA(message,1024,"error allocating array ");
				MessageBox(NULL, message, "Textures.exe", MB_OK);
				return( FALSE );
	}
		

	BITMAPFILEHEADER BFH;

	// Read in the Dib header and data.
	try{

		// Did we read in the entire BITMAPFILEHEADER?
		if( cf.Read( &BFH, sizeof( BITMAPFILEHEADER ) )
			!= sizeof( BITMAPFILEHEADER ) ||

			// Is the type 'MB'?
			BFH.bfType != 'MB' ||

			// Did we read in the remaining data?
			cf.Read( pDib, dwDibSize ) != dwDibSize )
			{
				StringCchPrintfA(message,1024,"error processing the file ");
				MessageBox(NULL, message, "Textures.exe", MB_OK);
			// Delete the memory if we had any
			// errors and return FALSE.
			delete [] pDib;
			return( FALSE );
			}
		}

modified 12-Mar-20 8:41am.

Richard MacCutchan12-Mar-20 0:36

12-Mar-20 0:36

And what is the problem and where does it occur?

And please use proper <pre> tags so your code is formatted properly. The code button at the top of the edit box provides proper formatting for most languages.

Calin Negru12-Mar-20 1:18

12-Mar-20 1:18

At the end of code posted above I try to do this:

StringCchPrintfA(message,1024,"dib at 34 %d",pDib[34]);
	MessageBox(NULL, message, "Textures.exe", MB_OK);

I expect pDib[34] to be 255 since the bitmap is 10 white pixels ( in a row) 40 bytes in total.

Richard MacCutchan12-Mar-20 3:31

12-Mar-20 3:31

I think you are missing something in your code. You read the BITMAPFILEHEADER but then assume that the remaining data is the actual bitmap, whereas the BITMAPFILEHEADER is followed by another header as described at BITMAPFILEHEADER (wingdi.h) - Win32 apps | Microsoft Docs[^].

Calin Negru12-Mar-20 5:40

12-Mar-20 5:40

yeah I was a bit in a hurry, I was expecting to find pixels right after the first header.

Richard MacCutchan12-Mar-20 6:10

12-Mar-20 6:10

It is all explained at Bitmap Header Types - Win32 apps | Microsoft Docs[^]. But take special care of the different header types that may exist.

Calin Negru13-Mar-20 4:22

13-Mar-20 4:22

I was only using a part of the bitmap processing code I was using as reference. I don`t need the palette part so I trimmed out a bit too much.

m_pDib = pDib;
	m_dwDibSize = dwDibSize;

	// Pointer our BITMAPINFOHEADER and RGBQUAD
	// variables to the correct place in the Dib data.
	m_pBIH = (BITMAPINFOHEADER *) m_pDib;
	m_pPalette =
		(RGBQUAD *) &m_pDib[sizeof(BITMAPINFOHEADER)];

	//	get image width and height
	m_width = m_pBIH->biWidth;
	m_height = m_pBIH->biHeight;

	// Calculate the number of palette entries.
	m_nPaletteEntries = 1 << m_pBIH->biBitCount;
	if( m_pBIH->biBitCount > 8 )
		m_nPaletteEntries = 0;
	else if( m_pBIH->biClrUsed != 0 )
		m_nPaletteEntries = m_pBIH->biClrUsed;

	// Point m_pDibBits to the actual Dib bits data.
	m_pDibBits =
		&m_pDib[sizeof(BITMAPINFOHEADER)+
			m_nPaletteEntries*sizeof(RGBQUAD)];

	// If we have a valid palette, delete it.
	if( m_Palette.GetSafeHandle() != NULL )
		m_Palette.DeleteObject();

I know I must go past the bitmapinfoheader to get to the pixels

modified 13-Mar-20 14:06pm.

Richard MacCutchan13-Mar-20 5:22

13-Mar-20 5:22

Please use proper <pre> tags around code blocks (and proper indentation), not Quoted text. The following code sample is preceded by
<pre lang="c++">
and followed by
</pre>

C++

// Calculate the number of palette entries.
m_nPaletteEntries = 1 << m_pBIH->biBitCount;
if( m_pBIH->biBitCount > 8 )
    m_nPaletteEntries = 0;
else if( m_pBIH->biClrUsed != 0 )
    m_nPaletteEntries = m_pBIH->biClrUsed;

Much more readable.

Calin Negru13-Mar-20 8:50

13-Mar-20 8:50

I`m having trouble understanding how this code works. The problem is I`m not a c expert.

cf.Read( &BFH, sizeof( BITMAPFILEHEADER )

For instance how does the portion of data read from my file fits into a structure. It`s not a structure of identical items BITMAPFILEHEADER is a mix of WORDs and DWORDS

Richard MacCutchan13-Mar-20 9:07

13-Mar-20 9:07

The sizeof operator gives the number of bytes in the object referred to. So in your case it will be the size of a BITMAPFILEHEADER, and the read operation will read the correct number of bytes into the structure. When complete each field of the structure should be correctly aligned*.

*There are conditions where this may not be true, so beware if you have a structure containing single byte elements. You may ignore that for the moment.

Calin Negru13-Mar-20 22:07

13-Mar-20 22:07

thanks that makes sense. In the code above do I need m_nPaletteEntries at all? Is used to calculate the offset at which individual pixels are stored?

Richard MacCutchan14-Mar-20 0:04

14-Mar-20 0:04

You need to examine the different items in the info table as described at BITMAPINFOHEADER structure (Windows) | Microsoft Docs[^]. The values of the items related to colours will tell you whether a colour table is included or not.

Calin Negru14-Mar-20 4:30

14-Mar-20 4:30

I have to take a short break. Your insight (last post included) is priceless Richard, thanks

`DreamLand Page` is my projects facebook page.

Richard MacCutchan14-Mar-20 4:47

14-Mar-20 4:47

Sorry to disappoint you, but my 'insight' is actually just a matter of reading the documentation.

Calin Negru14-Mar-20 8:11

14-Mar-20 8:11

the code you quoted is the bit that throws me into fog. What does the line that has the overload operator do?

Richard MacCutchan14-Mar-20 8:13

14-Mar-20 8:13

fearless_ wrote:
What does the line that has the overload operator do?

What line?

Calin Negru14-Mar-20 9:18

14-Mar-20 9:18

m_nPaletteEntries = 1 << m_pBIH->biBitCount;

phil.o14-Mar-20 9:37

phil.o

14-Mar-20 9:37

This is a bitwise left-shift operation which is equivalent to

C++

m_nPaletteEntries = pow(2, m_pBIH->biBitCount); // 2 to the power of bpp

What are shift operators in C++?[^]
This trick is used quite often, since a bitwise shift operation is way quicker than the pow() method, which is rather intense on processing time.

Edit: here's an interesting list of useful bitwise tricks:
Bit Twiddling Hacks[^]

"Five fruits and vegetables a day? What a joke!
Personally, after the third watermelon, I'm full."

Richard MacCutchan14-Mar-20 10:27

14-Mar-20 10:27

It's not pow, it's multiply by 2.