bitmap.cpp

//
// bitmap.cpp
//
// handle MS bitmap I/O. For portability, we don't use the data structure defined in Windows.h
// However, there is some strange thing, the side of our structure is different from what it 
// should though we define it in the same way as MS did. So, there is a hack, we use the hardcoded
// constanr, 14, instead of the sizeof to calculate the size of the structure.
// You are not supposed to worry about this part. However, I will appreciate if you find out the
// reason and let me know. Thanks.
//

#include "bitmap.h"
 
BMP_BITMAPFILEHEADER bmfh; 
BMP_BITMAPINFOHEADER bmih; 

unsigned char *readBMP(char *fname, int& width, int& height)
{ 
        FILE* file; 
        BMP_DWORD pos; 
 
        if ( (file=fopen( fname, "rb" )) == NULL )  
                return NULL; 
         
//      I am doing fread( &bmfh, sizeof(BMP_BITMAPFILEHEADER), 1, file ) in a safe way. :}
        fread( &(bmfh.bfType), 2, 1, file); 
        fread( &(bmfh.bfSize), 4, 1, file); 
        fread( &(bmfh.bfReserved1), 2, 1, file); 
        fread( &(bmfh.bfReserved2), 2, 1, file); 
        fread( &(bmfh.bfOffBits), 4, 1, file); 

        pos = bmfh.bfOffBits; 
 
        fread( &bmih, sizeof(BMP_BITMAPINFOHEADER), 1, file ); 
 
        // error checking
        if ( bmfh.bfType!= 0x4d42 ) {   // "BM" actually
                return NULL;
        }
        if ( bmih.biBitCount != 24 )  
                return NULL; 
/*
        if ( bmih.biCompression != BMP_BI_RGB ) {
                return NULL;
        }
*/
        fseek( file, pos, SEEK_SET ); 
 
        width = bmih.biWidth; 
        height = bmih.biHeight; 
 
        int padWidth = width * 3; 
        int pad = 0; 
        if ( padWidth % 4 != 0 ) 
        { 
                pad = 4 - (padWidth % 4); 
                padWidth += pad; 
        } 
        int bytes = height*padWidth; 
 
        unsigned char *data = new unsigned char [bytes]; 

        int foo = fread( data, bytes, 1, file ); 
        
        if (!foo) {
                delete [] data;
                return NULL;
        }

        fclose( file );
        
        // shuffle bitmap data such that it is (R,G,B) tuples in row-major order
        int i, j;
        j = 0;
        unsigned char temp;
        unsigned char* in;
        unsigned char* out;

        in = data;
        out = data;

        for ( j = 0; j < height; ++j )
        {
                for ( i = 0; i < width; ++i )
                {
                        out[1] = in[1];
                        temp = in[2];
                        out[2] = in[0];
                        out[0] = temp;

                        in += 3;
                        out += 3;
                }
                in += pad;
        }
                          
        return data; 
} 
 
void writeBMP(char *iname, int width, int height, unsigned char *data) 
{ 
        int bytes, pad;
        bytes = width * 3;
        pad = (bytes%4) ? 4-(bytes%4) : 0;
        bytes += pad;
        bytes *= height;

        bmfh.bfType = 0x4d42;    // "BM"
        bmfh.bfSize = sizeof(BMP_BITMAPFILEHEADER) + sizeof(BMP_BITMAPINFOHEADER) + bytes;
        bmfh.bfReserved1 = 0;
        bmfh.bfReserved2 = 0;
        bmfh.bfOffBits = /*hack sizeof(BMP_BITMAPFILEHEADER)=14, sizeof doesn't work?*/ 
                                         14 + sizeof(BMP_BITMAPINFOHEADER);

        bmih.biSize = sizeof(BMP_BITMAPINFOHEADER);
        bmih.biWidth = width;
        bmih.biHeight = height;
        bmih.biPlanes = 1;
        bmih.biBitCount = 24;
        bmih.biCompression = BMP_BI_RGB;
        bmih.biSizeImage = 0;
        bmih.biXPelsPerMeter = (int)(100 / 2.54 * 72);
        bmih.biYPelsPerMeter = (int)(100 / 2.54 * 72);
        bmih.biClrUsed = 0;
        bmih.biClrImportant = 0;

		// "w+b", not "wb" -- Eugene
        FILE *foo=fopen(iname, "w+b"); 

        //      fwrite(&bmfh, sizeof(BMP_BITMAPFILEHEADER), 1, foo);
        fwrite( &(bmfh.bfType), 2, 1, foo); 
        fwrite( &(bmfh.bfSize), 4, 1, foo); 
        fwrite( &(bmfh.bfReserved1), 2, 1, foo); 
        fwrite( &(bmfh.bfReserved2), 2, 1, foo); 
        fwrite( &(bmfh.bfOffBits), 4, 1, foo); 

        fwrite(&bmih, sizeof(BMP_BITMAPINFOHEADER), 1, foo); 

        bytes /= height;
        unsigned char* scanline = new unsigned char [bytes];
        for ( int j = 0; j < height; ++j )
        {
                memcpy( scanline, data + j*3*width, bytes );
                for ( int i = 0; i < width; ++i )
                {
                        unsigned char temp = scanline[i*3];
                        scanline[i*3] = scanline[i*3+2];
                        scanline[i*3+2] = temp;
                }
                fwrite( scanline, bytes, 1, foo);
        }

        delete [] scanline;

        fclose(foo);
}