CS50 Resize Code

resize.c

/**
 * copy.c
 *
 * Computer Science 50
 * Problem Set 4
 *
 * 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)
    {
        printf("Usage: ./resize n infile outfile\n");
        return 1;
    }

    // remember filenames
    int n = atoi(argv[1]);
    char* infile = argv[2];
    char* outfile = argv[3];

    // open input file 
    FILE* inptr = fopen(infile, "r");
    if (inptr == NULL)
    {
        printf("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 old_bf;
    fread(&old_bf, sizeof(BITMAPFILEHEADER), 1, inptr);

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

    // ensure infile is (likely) a 24-bit uncompressed BMP 4.0
    if (old_bf.bfType != 0x4d42 || old_bf.bfOffBits != 54 || old_bi.biSize != 40 || 
        old_bi.biBitCount != 24 || old_bi.biCompression != 0)
    {
        fclose(outptr);
        fclose(inptr);
        fprintf(stderr, "Unsupported file format.\n");
        return 4;
    }

    // create variable for the new header files
    BITMAPFILEHEADER new_bf;
    BITMAPINFOHEADER new_bi;
    
    // determine padding for scanlines
    int old_padding = (4 - (old_bi.biWidth * sizeof(RGBTRIPLE)) % 4) % 4;
    int new_padding = (4 - ((old_bi.biWidth * n) * sizeof(RGBTRIPLE)) % 4) % 4;
    
    // write outfile's BITMAPFILEHEADER
    fwrite(&old_bf, sizeof(BITMAPFILEHEADER), 1, outptr);
    
    // write outfile's BITMAPINFOHEADER
    fwrite(&old_bi, sizeof(BITMAPINFOHEADER), 1, outptr);
    
    // New element of BITMAPFILEHEADER
    new_bf.bfSize = sizeof(BITMAPFILEHEADER) + sizeof(BITMAPINFOHEADER) + (old_bi.biWidth * n * sizeof(RGBTRIPLE) + new_padding) * abs(old_bi.biHeight) * n;

    // New elements of BITMAPINFOHEADER
    new_bi.biHeight = old_bi.biHeight * n;
    new_bi.biWidth = old_bi.biWidth * n;
    new_bi.biSizeImage = (old_bi.biWidth * n * sizeof(RGBTRIPLE) + new_padding) * abs(old_bi.biHeight) * n;
    
    // write outfile's BITMAPFILEHEADER
    //fwrite(&new_bf, sizeof(BITMAPFILEHEADER), 1, outptr);
    
    // write outfile's BITMAPINFOHEADER
    //fwrite(&new_bi, sizeof(BITMAPINFOHEADER), 1, outptr);

    // iterate over infile's scanlines
    for (int i = 0, biHeight = abs(old_bi.biHeight); i < biHeight; i++)
    {
        //fseek(inptr, old_bi.biWidth * sizeof(RGBTRIPLE), SEEK_CUR);
        
        // iterate over pixels in scanline
        for (int j = 0; j < old_bi.biWidth; j++)
        {
            // temporary storage
            RGBTRIPLE triple;

            // read RGB triple from infile
            fread(&triple, sizeof(RGBTRIPLE), 1, inptr);
            
            // resize width n times
            for (int k = 0; k < n; k++)
            {
                // write RGB triple to outfile
                fwrite(&triple, sizeof(RGBTRIPLE), 1, outptr);
            }
        }
        
        // skip over padding, if any
        fseek(inptr, old_padding, SEEK_CUR);

        // then add it back (to demonstrate how)
        for (int m = 0; m < new_padding; m++)
        {
            fputc(0x00, outptr);
        }
    }

    // close infile
    fclose(inptr);

    // close outfile
    fclose(outptr);

    // that's all folks
    return 0;
}