CS50-04-problems - bottomup

https://cs50.harvard.edu/x/2023/problems/4/bottomup/

Bottom Up - CS50x 2023

외부 파일을 다루는 과정으로 처음 들어가는 연습문제로, 코드 4줄만 추가하면 되는 간단한 문제이다.

 

좌측 이미지를 우측으로 바꿈. 헤더만 건들면 된다.

Bottomup.c

// Copies a BMP file

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

#include "bmp.h"

int main(int argc, char *argv[])
{
    // Ensure proper usage
    if (argc != 3)
    {
        printf("Usage: copy infile outfile\n");
        return 1;
    }

    // Remember filenames
    char *infile = argv[1];
    char *outfile = argv[2];

    // 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);
        printf("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);
        printf("Unsupported file format.\n");
        return 4;
    }

    if (bi.biHeight < 0)     //여기서부터
    {
        bi.biHeight = -(bi.biHeight);
    }  //여기까지만 추가된 부분

    // Write outfile's BITMAPFILEHEADER
    fwrite(&bf, sizeof(BITMAPFILEHEADER), 1, outptr);

    // Write outfile's BITMAPINFOHEADER
    fwrite(&bi, sizeof(BITMAPINFOHEADER), 1, outptr);

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

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

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

            // Write RGB triple to outfile
            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 < padding; k++)
        {
            fputc(0x00, outptr);
        }
    }

    // Close infile
    fclose(inptr);

    // Close outfile
    fclose(outptr);

    // Success
    return 0;
}

 

 

bmp.h 파일 (완성본 제공)

// BMP-related data types based on Microsoft's own

#include <stdint.h>

// Aliases for C/C++ primitive data types
// https://msdn.microsoft.com/en-us/library/cc230309.aspx
typedef uint8_t  BYTE;
typedef uint32_t DWORD;
typedef int32_t  LONG;
typedef uint16_t WORD;

// Information about the type, size, and layout of a file
// 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;

// Information about the dimensions and color format
// 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;

// Relative intensities of red, green, and blue
// https://msdn.microsoft.com/en-us/library/dd162939(v=vs.85).aspx
typedef struct
{
    BYTE rgbtBlue;
    BYTE rgbtGreen;
    BYTE rgbtRed;
} __attribute__((__packed__))
RGBTRIPLE;

 

 

 

biHeight : 비트맵의 세로 픽셀 수.

이 값이 양수이면 DIB는 아래에서 위로 구성(Bottom-Up)되며, 원점은 좌하단이 된다.

이 값이 음수이면 DIB는 위에서 아래로 구성(Top-Down)되며, 원점은 좌상단이 된다.

https://m.blog.naver.com/PostView.naver?isHttpsRedirect=true&blogId=genofreedomi&logNo=220433010884 

BITMAPFILEHEADER, BITMAPINFOHEADER 구조체