Subj : Problems writing BMP File
To   : comp.programming.threads
From : Stephan
Date : Fri Mar 11 2005 10:32 pm

Hi

I wanted to write a routine, that writes a BMP file.
SO I took some code written for Windows. Unfortunately
I work under Linux, so I can't include the mmsystem.h

The generated BMP files are corrupt. I think it has to do
something with the structs I had to build on my own, but don't
know what.

here is the code that I'm speaking of.

#include <iostream>
#include <GL/gl.h>
using namespace std;

typedef unsigned short WORD;
typedef unsigned int DWORD;
typedef long LONG;

typedef struct tagBITMAPINFOHEADER{
   DWORD  biSize;
   LONG   biWidth;
   LONG   biHeight;
   WORD   biPlanes;
   WORD   biBitCount;
   DWORD  biCompression;
   DWORD  biSizeImage;
   LONG   biXPelsPerMeter;
   LONG   biYPelsPerMeter;
   DWORD  biClrUsed;
   DWORD  biClrImportant;
} BITMAPINFOHEADER, *PBITMAPINFOHEADER;

typedef struct tagBITMAPFILEHEADER {
   WORD    bfType;
   DWORD   bfSize;
   WORD    bfReserved1;
   WORD    bfReserved2;
   DWORD   bfOffBits;
} BITMAPFILEHEADER, *PBITMAPFILEHEADER;


int screenshot(int x, int y, int Width, int Height, const char *fname)
{
    BITMAPFILEHEADER bf;
    BITMAPINFOHEADER bi;

    unsigned char *image = (unsigned char*)malloc(sizeof(unsigned 
char)*Width*Height*3);
    FILE *file = fopen(fname, "wb");

    if( image!=NULL )
    {
       if( file!=NULL )
       {
          glReadPixels( x, y, Width, Height, GL_BGR_EXT, 
GL_UNSIGNED_BYTE, image );

          memset( &bf, 0, sizeof( bf ) );
          memset( &bi, 0, sizeof( bi ) );

          bf.bfType = 'MB';
          bf.bfSize = sizeof(bf)+sizeof(bi)+Width*Height*3;
          bf.bfOffBits = sizeof(bf)+sizeof(bi);
          bi.biSize = sizeof(bi);
          bi.biWidth = Width;
          bi.biHeight = Height;
          bi.biPlanes = 1;
          bi.biBitCount = 24;
          bi.biSizeImage = Width*Height*3;

          fwrite( &bf, sizeof(bf), 1, file );
          fwrite( &bi, sizeof(bi), 1, file );
          fwrite( image, sizeof(unsigned char), Height*Width*3, file );

          fclose( file );
       }
       free( image );
    }
    return 0;
}

Maybe someone can point me to the misstake

Regards

Stephan

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