resize - v2

/**
 * Copies a BMP piece by piece, just because.
 */

#include <stdio.h>
#include <stdlib.h>
/**
 * BMP-related data types based on Microsoft's own.
 */

#include <stdint.h>

/**
 * Common Data Types
 *
 * The data types in this section are essentially aliases for C/C++
 * primitive data types.
 *
 * Adapted from https://msdn.microsoft.com/en-us/library/cc230309.aspx.
 * See http://en.wikipedia.org/wiki/Stdint.h for more on stdint.h.
 */
typedef uint8_t  BYTE;
typedef uint32_t DWORD;
typedef int32_t  LONG;
typedef uint16_t WORD;

/**
 * BITMAPFILEHEADER
 *
 * The BITMAPFILEHEADER structure contains information about the type, size,
 * and layout of a file that contains a DIB [device-independent bitmap].
 *
 * Adapted from https://msdn.microsoft.com/en-us/library/dd183374(v=vs.85).aspx.
 */
typedef struct
{
    WORD bfType;
    DWORD bfSize;
    WORD bfReserved1;
    WORD bfReserved2;
    DWORD bfOffBits;
} __attribute__((__packed__))
BITMAPFILEHEADER;

/**
 * BITMAPINFOHEADER
 *
 * The BITMAPINFOHEADER structure contains information about the
 * dimensions and color format of a DIB [device-independent bitmap].
 *
 * Adapted from https://msdn.microsoft.com/en-us/library/dd183376(v=vs.85).aspx.
 */
typedef struct
{
    DWORD biSize;
    LONG biWidth;
    LONG biHeight;
    WORD biPlanes;
    WORD biBitCount;
    DWORD biCompression;
    DWORD biSizeImage;
    LONG biXPelsPerMeter;
    LONG biYPelsPerMeter;
    DWORD biClrUsed;
    DWORD biClrImportant;
} __attribute__((__packed__))
BITMAPINFOHEADER;

/**
 * RGBTRIPLE
 *
 * This structure describes a color consisting of relative intensities of
 * red, green, and blue.
 *
 * Adapted from https://msdn.microsoft.com/en-us/library/dd162939(v=vs.85).aspx.
 */
typedef struct
{
    BYTE rgbtBlue;
    BYTE rgbtGreen;
    BYTE rgbtRed;
} __attribute__((__packed__))
RGBTRIPLE;







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

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

    printf("Factor = %i\n", factor);

    // 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;
    }


    int padding_old = (4 - (bi.biWidth * sizeof(RGBTRIPLE)) % 4) % 4;

    //debugging (although not necessary 'cause there's )
    printf("biWidth = %d \nbiHeight = %d \nbiSizeImage = %d \nbfSize = %d \n", bi.biWidth, bi.biHeight, bi.biSizeImage, bf.bfSize);

    //increasing height and width by factor
    bi.biWidth *= factor;
    bi.biHeight *= factor;

    //calculating padding from new width
    int padding = (4 - (bi.biWidth * sizeof(RGBTRIPLE)) % 4) % 4;

    //calculating new sizes for headings
    bi.biSizeImage = ((sizeof(RGBTRIPLE) * bi.biWidth) + padding) * abs(bi.biHeight);
    bf.bfSize = bi.biSizeImage + sizeof(BITMAPFILEHEADER) + sizeof(BITMAPINFOHEADER);

    //just for debugging:
    printf("biWidth = %d \nbiHeight = %d \nbiSizeImage = %d \nbfSize = %d \npadding_old = %d \npadding_new = %d \n", bi.biWidth, bi.biHeight, bi.biSizeImage, bf.bfSize, padding_old, 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, biHeight = abs(bi.biHeight); i < (biHeight / factor); i++)
    {
        // iterate over pixels in scanline
        for (int l = 0; l < factor; l++)
        {
            //resize vertically
            for (int j = 0; j < (bi.biWidth / factor); j++)
            {
                // temporary storage
                RGBTRIPLE triple;

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


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

            // write new padding
            for (int k = 0; k < padding; k++)
            {
                fputc(0x00, outptr);
            }

            //measure of control, to ensure the file pointer is still at the same point.
            fseek(inptr, 0, SEEK_CUR);

            //go back to the begining of the input file's line to rewrite it as many times as we are resizing it
            if (l < factor - 1)
            {
                fseek(inptr, -(bi.biWidth/factor), SEEK_CUR);
            }
        }

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


    // close infile
    fclose(inptr);

    // close outfile
    fclose(outptr);

    // success
    return 0;
}