resize.c - shared from CS50 IDE

resize.c

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

#include "bmp.h"

int main(int argc, char* argv[])
{
    // ensure proper usage
    if (argc != 4)
    {
        printf("Usage: ./copy infile outfile\n");
        return 1;
    }
    
    // String to an int
    int rescale = atoi(argv[1]);
    
    // ensure rescale is a positive int, less than or equal to 100
    if (rescale < 1 || rescale > 100)
    {
        printf("Rescale must be a positive int, less than or equal to 100!\n");
        return 2;
    }
    
    // remember filenames
    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 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 4;
    }
    
    // update header info
    BITMAPFILEHEADER bfnew;
    BITMAPINFOHEADER binew;
    
    bfnew = bf;
    binew = bi;
    
    binew.biWidth *= rescale;
    binew.biHeight *= rescale;
    
    // determine padding for scanline
    int oldpadding = (4 - (bi.biWidth * sizeof(RGBTRIPLE)) % 4) % 4;
    int padding = (4 - (binew.biWidth * sizeof(RGBTRIPLE)) % 4) % 4;
    
    // update bi.biSizeImage && bfSize for new image
    binew.biSizeImage = abs(binew.biHeight) * (abs(binew.biWidth) * sizeof(RGBTRIPLE) + padding);
    bfnew.bfSize = bfnew.bfOffBits + binew.biSizeImage;

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

    // write outfile's BITMAPINFOHEADER
    fwrite(&binew, sizeof(BITMAPINFOHEADER), 1, outptr);
    
    // iterate over infile's scanlines
    for (int i = 0, biHeight = abs(bi.biHeight); i < biHeight; i++)
    {
        // iterate rescale no. times
        for (int x =0; x < rescale; x++)
        {
            
        // iterate over pixels in scanline
        for (int j = 0; j < bi.biWidth; j++)
        {
            
            // declare a variable that can store negative values
            long offset = bi.biWidth * sizeof(RGBTRIPLE);
            
            // temporary storage
            RGBTRIPLE triple;
            
            // read RGB triple from infile
            fread(&triple, sizeof(RGBTRIPLE), 1, inptr);
            
            // go back to the begining of scanline
            if (i % rescale != 0)
            {
                fseek(inptr, -offset, SEEK_CUR);
            }
            
            for (int l = 0; l < rescale; l++)
            {
            // write RGB triple to outfile
            fwrite(&triple, sizeof(RGBTRIPLE), 1, outptr);
            }
            
            // go to the next row
            fseek(inptr, binew.biWidth * sizeof(RGBTRIPLE) + oldpadding, SEEK_CUR);
        }
        
        // then add it back (to demonstrate how)
        for (int k = 0; k < padding; k++)
        {
            fputc(0x00, outptr);
        }
        
        }
        
        // skip over padding, if any
        fseek(inptr, oldpadding, SEEK_CUR);

    }

    // close infile
    fclose(inptr);