CS50 pset4 - "Resize"

resize.c

/**
 * resize.c
 *
 * Computer Science 50
 * Problem Set 4
 *
 * Copies a BMP piece by piece, but also resizes it, 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 factor infile outfile\n");
        return 1;
    }

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

    // check factor
    if (factor < 1 || factor > 100)
    {
        printf("Factor must be in the range [1-100]\n");
        return 1;
    }

    // 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 bf;
    BITMAPFILEHEADER bf_new;
    fread(&bf, sizeof(BITMAPFILEHEADER), 1, inptr);
    
    bf_new = bf;

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

    // 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;
    }

    // set new width and height dimensions
    bi_new.biWidth = bi.biWidth * factor;
    bi_new.biHeight = bi.biHeight * factor;

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

    // set new file size
    bf_new.bfSize = 54 + (bi_new.biWidth * sizeof(RGBTRIPLE) + new_padding) * abs(bi_new.biHeight);
    bi_new.biSizeImage = bf_new.bfSize - 54;
    

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

    // write outfile's BITMAPINFOHEADER
    fwrite(&bi_new, sizeof(BITMAPINFOHEADER), 1, outptr);
    
    // iterate over infile's scanlines
    for (int i = 0, biHeight = abs(bi.biHeight); i < biHeight; i++)
    {
        // each row will be printed out factor times
        int rowcounter = 0;
        
        while (rowcounter < factor)
        {
            
            // iterate over pixels in scanline
            for (int j = 0; j < bi.biWidth; j++)
            {
                // temporary storage
                RGBTRIPLE triple;
                
                // each pixel will be printed out factor times
                int pixelcounter = 0;

                // read RGB triple from infile
                fread(&triple, sizeof(RGBTRIPLE), 1, inptr);
            
                // write RGB triple to outfile
                while (pixelcounter < factor)
                {
                    fwrite(&triple, sizeof(RGBTRIPLE), 1, outptr);
                    pixelcounter++;
                }
            }
            
            // add new padding
            for (int k = 0; k < new_padding; k++)
                fputc(0x00, outptr);
            
            // seek back to the beginning of row in input file, but not after iteration of printing
            if (rowcounter < (factor - 1))
                fseek(inptr, -(bi.biWidth * sizeof(RGBTRIPLE)), SEEK_CUR);
            
            rowcounter++;
        }
        
        // skip over padding, if any
        fseek(inptr, padding, SEEK_CUR);
    }
    
    // close infile
    fclose(inptr);

    // close outfile
    fclose(outptr);

    // that's all folks
    return 0;
}

Having a look at your code has helped me immensely understand my problems, so thank you.

Взгляд на ваш код помог мне безмерно понять мои проблемы, так что спасибо.

👍❤️