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Loading A BMP

Started by The Reindeer Effect Jun 2, 2002 at 9:04 PM 5 replies 250+ views

Original Post

Jun 2, 2002 at 9:04 PM

I am having some problems with a little project of mine. I really haven''t learned C file I/O functions the way I should have I assume. Anyways ... I can load the BITMAPFILEHEADER and BITMAPINFOHEADER just fine. Since it is a 24-bit bmp, I assume that means that there is no pallete. So I go directly onto trying to load the pixel data ... but I have no clue how to. I had planned to store the pixel data in - BYTE* pData; Whenever I find the biWidth and biHeight, I do - pData = new BYTE[ 3 * biWidth * biHeight]. Then: temp = 3 * biWidth * biHeight; for( int i = 0; i < temp; i++) fread( &pData, sizeof( BYTE ), 1, in ); for some reason I am having problems ... cuz I impelented a test. I tried to output all the data basically the same way i got it, cept i used fwrite( .. ); When I try to open the file, it says not a current bmp file formay. After tinkering for 20 minutes, I have only managed to make a 593 mb file, the original is like 50k ------------------- The Reindeer Effect

Null and Void

163

Null and Void

Jun 2, 2002 at 9:06 PM

Here's my code for reading Windows bitmaps. It's fairly easy to understand, even though it's very non-standard code:

  
using namespace gPixmapFormat;

gImageWinBmpHeader Header;
gImageWinBmpInfoHeader Info;
unsigned int ByteWidth, BytesPP, DataSize, Shift;

File.Read(&Header,14,1);
File.Read(&Info,40,1);

/* This doesn't ever seem to work for me ;)
if(Header.OffBits > (14 + 40))
	File.Seek(Header.OffBits - (14 + 40),SEEK_CUR);
*/

// Flip little endian data to native endian data

gEndianFixLittle(Header.OffBits);
gEndianFixLittle(Header.Type);
gEndianFixLittle(Info.Width);
gEndianFixLittle(Info.Height);
gEndianFixLittle(Info.BitCount);

if(Header.Type != 0x4D42) {
	gError("This isn't a Win32 bitmap.");
}
if(Info.BitCount != 24) {
	gError("This bit depth isn't supported.");
}

BytesPP = Info.BitCount/8;
ByteWidth = Info.Width * BytesPP;
DataSize = ByteWidth * Info.Height;
Shift = ByteWidth % 4;

This->SetBytesPP(BytesPP);
This->SetWidth(Info.Width);
This->SetHeight(Info.Height);
This->SetData(gNewArray(gByte,DataSize));
This->SetFreeMem(true);

if(Shift == 0) {
	File.Read(This->GetData(),1,DataSize);
} else { // Yeah, padding...

	for(unsigned int a=0; a<Info.Height; ++a) {
		File.Read(This->GetData(),1,ByteWidth);
		File.Seek(Shift,SEEK_CUR);
	}
}

This->SetFormat(External::BGR);

This->FlipVert();

About that last part: Are you loading and saving it in binary mode (the default in Windows is text mode)?

[edited by - Null and Void on June 2, 2002 10:10:05 PM]

The Reindeer Effect

Author

The Reindeer Effect

Jun 2, 2002 at 9:07 PM

What headers / libs do I need to use that?

[edited by - The Reindeer Effect on June 2, 2002 10:13:07 PM]

Null and Void

163

Null and Void

Jun 2, 2002 at 9:16 PM

Sorry about the ''update right after I post'' thing, I hit reply too quickly.

quote:
Original post by The Reindeer Effect
What headers / libs do I need to use that?

Well, you''d need most of my GTW engine

. I was posting it as a ''reference'' for you to go by. Some notes: My file functions are based directly off the C file I/O functions (but they throw exceptions on error), and my gWinBmp*Header structs are just like the Win32 API''s BITMAP*HEADER structs (I needed my own copy to maintain portability).