resize pset 4

/**
 * resize.c
 *
 * Computer Science 50
 * Problem Set 4
 *
 * resize bmp by factor n.
 */

#include <stdio.h>
#include <stdlib.h>

#include "bmp.h"

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

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

    if (n < 1 || n > 100)
    {
        printf("Please enter resize factor between 1 & 100");
        return 2;
    }

    // open input file
    FILE* inptr = fopen(infile, "r");
    if (inptr == NULL)
    {
        printf("Could not open %s.\n", infile);
        return 3;
    }

    // open output file
    FILE* outptr = fopen(outfile, "w");
    if (outptr == NULL)
    {
        fclose(inptr);
        fprintf(stderr, "Could not create %s.\n", outfile);
        return 4;
    }

    // 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 5;
    }

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

    //create new header files
    BITMAPFILEHEADER newbf = bf;
    BITMAPINFOHEADER newbi = bi;

    newbi.biWidth = bi.biWidth * n;
    newbi.biHeight = 0x100000000 - (abs(bi.biHeight) * n);

    int newPadding = (4 - (newbi.biWidth * sizeof(RGBTRIPLE)) % 4) % 4;

    newbi.biSizeImage = (newbi.biWidth * abs(newbi.biHeight)) * sizeof(RGBTRIPLE) + (newPadding * abs(newbi.biHeight));
    newbf.bfSize = newbi.biSizeImage + sizeof(BITMAPFILEHEADER) + sizeof(BITMAPINFOHEADER);

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

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



    // iterate over infile's scanlines
    for (int i = 0, biHeight = abs(newbi.biHeight); i < biHeight; i++)
    {
        // iterate over pixels in scanline
        for (int j = 0; j < n; j++)
        {
            for (int k = 0; k < bi.biWidth; k++)
            {
                // temporary storage
                RGBTRIPLE triple;

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

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

            // skip over padding, if any
            fseek(inptr, padding, SEEK_CUR);

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

    // close infile
    fclose(inptr);

    // close outfile
    fclose(outptr);

    // that's all folks
    return 0;
}