c++ - 在 C++ 中读取 .bmp 文件

Question

我正在尝试加载一个 bmp 文件以便在 opengl 中重复使用它。我通过谷歌找到了一些关于如何加载 bmp 文件的代码。我拿了这段代码并在我的项目中放入了一个类位图。这个类离结束还很远，但文件头的读取已经出错了。读取 INFOHEADER 和 FILEHEADER 的字节后，我的结构中没有正确的值。一些想法？

//
//  Bitmap.h
//

#ifndef LaserMaze_Bitmap_h
#define LaserMaze_Bitmap_h

typedef struct                       /**** BMP file header structure ****/
{
    unsigned short bfType;           /* Magic number for file */
    unsigned int   bfSize;           /* Size of file */
    unsigned short bfReserved1;      /* Reserved */
    unsigned short bfReserved2;      /* ... */
    unsigned int   bfOffBits;        /* Offset to bitmap data */
} BITMAPFILEHEADER;

#  define BF_TYPE 0x4D42             /* "MB" */

typedef struct                       /**** BMP file info structure ****/
{
    unsigned int   biSize;           /* Size of info header */
    int            biWidth;          /* Width of image */
    int            biHeight;         /* Height of image */
    unsigned short biPlanes;         /* Number of color planes */
    unsigned short biBitCount;       /* Number of bits per pixel */
    unsigned int   biCompression;    /* Type of compression to use */
    unsigned int   biSizeImage;      /* Size of image data */
    int            biXPelsPerMeter;  /* X pixels per meter */
    int            biYPelsPerMeter;  /* Y pixels per meter */
    unsigned int   biClrUsed;        /* Number of colors used */
    unsigned int   biClrImportant;   /* Number of important colors */
} BITMAPINFOHEADER;

/*
 * Constants for the biCompression field...
 */

#  define BI_RGB       0             /* No compression - straight BGR data */
#  define BI_RLE8      1             /* 8-bit run-length compression */
#  define BI_RLE4      2             /* 4-bit run-length compression */
#  define BI_BITFIELDS 3             /* RGB bitmap with RGB masks */

typedef struct                       /**** Colormap entry structure ****/
{
    unsigned char  rgbBlue;          /* Blue value */
    unsigned char  rgbGreen;         /* Green value */
    unsigned char  rgbRed;           /* Red value */
    unsigned char  rgbReserved;      /* Reserved */
} RGBQUAD;

class Bitmap {
public:
    Bitmap(const char* filename);
    ~Bitmap();
    RGBQUAD* pixels;
    BITMAPFILEHEADER fh;
    BITMAPINFOHEADER ih;

    private:

};

#endif

中国共产党

//  Bitmap.cpp
//

#include <iostream>
#include <stdio.h>

#include "Bitmap.h"

Bitmap::Bitmap(const char* filename) {
    FILE* file;
    file = fopen(filename, "rb");

    std::cout << sizeof(BITMAPFILEHEADER) << std::endl;

    if(file != NULL) { // file opened
        BITMAPFILEHEADER h;
        size_t x = fread(&h, sizeof(BITMAPFILEHEADER), 1, file); //reading the FILEHEADER

        std::cout << x;
        fread(&this->ih, sizeof(BITMAPINFOHEADER), 1, file);

        fclose(file);
    }
}

Answer 1

header 需要 2 字节对齐。

#pragma pack(2) // Add this

typedef struct
{
    unsigned short bfType;
    unsigned int   bfSize;
    unsigned short bfReserved1;
    unsigned short bfReserved2;
    unsigned int   bfOffBits;
} BITMAPFILEHEADER;

#pragma pack() // and this