resize.txt

/**
 * Copies a BMP piece by piece, just because.
 */
       
#include <stdio.h>
#include <stdlib.h>

#include "bmp.h"

int main(int argc, char *argv[])
{
    // ensure proper usage
    if (argc != 4)
    {
        fprintf(stderr, "Usage: ./resize n infile outfile\n");
        return 1;
    }


    int n = atoi(argv[1]);
    if (n < 1 && n > 100) 
    {
        fprintf(stderr, "Must enter a positive integer 100 or less");
        return 1;
    }
    // remember filenames
    char *infile = argv[2];
    char *outfile = argv[3];

    // open input file 
    FILE *inptr = fopen(infile, "r");
    if (inptr == NULL)
    {
        fprintf(stderr, "Could not open %s.\n", infile);
        return 2;
    }

    // open output file
    FILE *outptr = fopen(outfile, "w");
    if (outptr == NULL)
    {
        fclose(inptr);
        fprintf(stderr, "Could not create %s.\n", outfile);
        return 3;
    }

    // read infile's BITMAPFILEHEADER
    BITMAPFILEHEADER bf;
    fread(&bf, sizeof(BITMAPFILEHEADER), 1, inptr);

    // read infile's BITMAPINFOHEADER
    BITMAPINFOHEADER bi;
    fread(&bi, sizeof(BITMAPINFOHEADER), 1, inptr);

    // ensure infile is (likely) a 24-bit uncompressed BMP 4.0
    if (bf.bfType != 0x4d42 || bf.bfOffBits != 54 || bi.biSize != 40 || 
        bi.biBitCount != 24 || bi.biCompression != 0)
    {
        fclose(outptr);
        fclose(inptr);
        fprintf(stderr, "Unsupported file format.\n");
        return 4;
    }
    
    // save infile values of biHeight and biWidth for use when reading later
    int infile_biHeight = abs(bi.biHeight);
    int infile_biWidth = bi.biWidth;
    int pointer_move = infile_biWidth * sizeof(RGBTRIPLE);
    
    
    // determine padding for scanlines
    int infile_padding = (4 - (bi.biWidth * sizeof(RGBTRIPLE)) % 4) % 4;

    //change header variables for scaling at n
    bi.biWidth *= n;
    bi.biHeight *= n;
    int outfile_padding = (4 - (bi.biWidth * sizeof(RGBTRIPLE)) % 4) % 4;
    bi.biSizeImage = ((sizeof(RGBTRIPLE) * bi.biWidth) + outfile_padding) * abs(bi.biHeight);
    bf.bfSize = bi.biSizeImage + sizeof(BITMAPFILEHEADER) + sizeof(BITMAPINFOHEADER);

    // write outfile's BITMAPFILEHEADER
    fwrite(&bf, sizeof(BITMAPFILEHEADER), 1, outptr);

    // write outfile's BITMAPINFOHEADER
    fwrite(&bi, sizeof(BITMAPINFOHEADER), 1, outptr);

    

    // iterate over infile's scanlines
    for (int i = 0; i < infile_biHeight; i++)
    {
        //scale the rows n times
        for (int m = 0; m < n; m++)
        {
            // iterate over pixels in scanline
            for (int j = 0; j < infile_biWidth; j++)
            {
                // temporary storage
                RGBTRIPLE triple;

                // read RGB triple from infile
                fread(&triple, sizeof(RGBTRIPLE), 1, inptr);

                // write RGB triple to outfile
                for (int k = 0; k < n; k++)
                    fwrite(&triple, sizeof(RGBTRIPLE), 1, outptr);
                
            }
            
            // write the outfile padding
            for (int p = 0; p < outfile_padding; p++)
                fputc(0x00, outptr);
                    
            //return to the beginning of the input_file scanline
            if (m < n - 1) 
                fseek(inptr, -pointer_move, SEEK_CUR);
                    
        }
           
        // skip over padding, if any
        fseek(inptr, infile_padding, SEEK_CUR);
    }

    // close infile
    fclose(inptr);

    // close outfile
    fclose(outptr);

    // success
    return 0;
}