resize.c

// resizes bmp file

#include <math.h>
#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]);

    // ensure n is positive and no more than 100
    if (n > 100 || n < 1)
    {
        fprintf(stderr, "n must be a positive integer less than or equal to 100\n");
        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 1;
    }

    // open output file
    FILE *outptr = fopen(outfile, "w");
    if (outptr == NULL)
    {
        fclose(inptr);
        fprintf(stderr, "Could not create %s.\n", outfile);
        return 1;
    }

    // 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;
    }

     // stores infiles' dimensions
    int inHeight = bi.biHeight;
    int inWidth = bi.biWidth;

    // update the dimensions of the image
    bi.biHeight = bi.biHeight * n;
    bi.biWidth = bi.biWidth * n;

    // determine padding for scanlines
    int out_padding = (4 - (bi.biWidth * sizeof(RGBTRIPLE)) % 4) % 4;
    int in_padding = (4 - (inWidth * sizeof(RGBTRIPLE)) % 4) % 4;

    // update the size of the image
    bf.bfSize = sizeof(BITMAPFILEHEADER) + sizeof(BITMAPINFOHEADER) + ((bi.biWidth * abs(bi.biHeight)) * sizeof(RGBTRIPLE)) + out_padding;

    // 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, Height = abs(inHeight); i < Height; i++)
    {
        // write n scanlines to outfile per scanline on infile
        for (int m = 0; m < n; m++)
        {
            // iterate over pixels in infile's scanline
            for (int j = 0; j < inWidth; j++)
            {
                // temporary storage
                RGBTRIPLE triple;

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

                // write RGB triple to outfile n times
                for (int l = 0; l < n; l++)
                {
                    fwrite(&triple, sizeof(RGBTRIPLE), 1, outptr);
                }
            }

            // change offset to the beginning of scanline if this isn't the last iteration of the loop
            if (m != n - 1)
            {
                fseek(inptr, (inWidth * sizeof(RGBTRIPLE)) * -1, SEEK_CUR);
            }

            // add the padding on outfile
            for (int k = 0; k < out_padding; k++)
            {
                fputc(0x00, outptr);
            }
        }

        // skip over padding on infile
        fseek(inptr, in_padding, SEEK_CUR);
    }

    // close infile
    fclose(inptr);

    // close outfile
    fclose(outptr);

    // success
    return 0;
}