Question

我的源代码出错，这基本上导致位图图像显得过宽。例如，它将打印宽度和高度，高度是完美的（256），宽度也应该是256，但程序说它是数十亿像素宽，每次都是不同的。这是源代码。

#include "glob.h"

/* Image type - contains height, width, and data */
struct Image {
    unsigned long sizeX;
    unsigned long sizeY;
    char *data;
};
typedef struct Image Image;

int ImageLoad(char *filename, Image *image) {
    FILE *file;
    unsigned long size;                 // size of the image in bytes.
    unsigned long i;                    // standard counter.
    unsigned short int planes;          // number of planes in image (must be 1)
    unsigned short int bpp;             // number of bits per pixel (must be 24)
    char temp;                          // temporary color storage for bgr-rgb conversion.

    // make sure the file is there.
    if ((file = fopen(filename, "rb"))==NULL){
        printf("bitmap Not Found : %s\n",filename);
        return 0;
    }

    // seek through the bmp header, up to the width/height:
    fseek(file, 18, SEEK_CUR);

    // read the width
    if ((i = fread(&image->sizeX, 4, 1, file)) != 1) {
        printf("Error reading width from %s.\n", filename);
        return 0;
    }
    printf("Width of %s: %lu\n", filename, image->sizeX);

    // read the height
    if ((i = fread(&image->sizeY, 4, 1, file)) != 1) {
        printf("Error reading height from %s.\n", filename);
        return 0;
    }
    printf("Height of %s: %lu\n", filename, image->sizeY);

    // calculate the size (assuming 24 bits or 3 bytes per pixel).
    size = image->sizeX * image->sizeY * 3;

    // read the planes
    if ((fread(&planes, 2, 1, file)) != 1) {
        printf("Error reading planes from %s.\n", filename);
        return 0;
    }
    if (planes != 1) {
        printf("Planes from %s is not 1: %u\n", filename, planes);
        return 0;
    }

    // read the bpp
    if ((i = fread(&bpp, 2, 1, file)) != 1) {
        printf("Error reading bpp from %s.\n", filename);
        return 0;
    }
    if (bpp != 24) {
        printf("Bpp from %s is not 24: %u\n", filename, bpp);
        return 0;
    }

    // seek past the rest of the bitmap header.
    fseek(file, 24, SEEK_CUR);

    // read the data.
    image->data = (char *) malloc(size);
    if (image->data == NULL) {
        printf("Error allocating memory for color-corrected image data\n");
        return 0;
    }

    if ((i = fread(image->data, size, 1, file)) != 1) {
        printf("Error reading image data from %s.\n", filename);
        return 0;
    }

    for (i=0; i<size; i+=3) { // reverse all of the colors. (bgr -> rgb)
        temp = image->data[i];
        image->data[i] = image->data[i+2];
        image->data[i+2] = temp;
    }

    // we're done.
    return 0;
}

// Load Bitmaps And Convert To Textures
void glob::LoadGLTextures() {
    // Load Texture
    Image *image1;

    // allocate space for texture
    image1 = (Image *) malloc(sizeof(Image));
    if (image1 == NULL) {
        printf("(image1 == NULL)\n");
        exit(0);
    }

    ImageLoad("data/textures/NeHe.bmp", image1);

    // Create Texture
    glGenTextures(1, &texture);
    glBindTexture(GL_TEXTURE_2D, texture);   // 2d texture (x and y size)

    glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MAG_FILTER,GL_LINEAR); // scale linearly when image bigger than texture
    glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MIN_FILTER,GL_LINEAR); // scale linearly when image smalled than texture

    // 2d texture, level of detail 0 (normal), 3 components (red, green, blue), x size from image, y size from image,
    // border 0 (normal), rgb color data, unsigned byte data, and finally the data itself.
    glTexImage2D(GL_TEXTURE_2D, 0, 3, image1->sizeX, image1->sizeY, 0, GL_RGB, GL_UNSIGNED_BYTE, image1->data);
};

glob.h是这样的：

#ifndef GLOB_H_INCLUDED
#define GLOB_H_INCLUDED

#include <iostream>
#include <stdlib.h>
#include <stdio.h>      // Header file for standard file i/o.

#include <GL/glx.h>    /* this includes the necessary X headers */
#include <GL/gl.h>
//#include <GL/glut.h>    // Header File For The GLUT Library
//#include <GL/glu.h>   // Header File For The GLu32 Library

#include <X11/X.h>    /* X11 constant (e.g. TrueColor) */
#include <X11/keysym.h>

class glob {
    bool Running;
    GLuint texture; //make an array when we start using more then 1
    Display     *dpy;
    Window       win;
    XEvent       event;
    GLboolean    doubleBuffer;
    GLboolean    needRedraw;
    GLfloat      xAngle, yAngle, zAngle;
    float        camera_x, camera_y, camera_z;
public:
    glob();
    int OnExecute();
public:
    int init(int argc, char **argv);
    void LoadGLTextures();
    void OnEvent();
    void redraw(void);
};

#endif // GLOB_H_INCLUDED

任何人都可以帮我解决这个问题吗？

Answer 1

很多事情都可能出错。

如果它是一个非常旧的文件，它可能有一个BITMAPCOREHEADER，其大小字段每个只有2个字节。

你的机器是小端吗？ BMP文件以little endian存储。

请注意，高度可能是负数（这意味着它是一个自上而下的位图，而不是自下而上的位图）。如果将小的负数解释为无符号的32位int，您将看到数十亿的值。

此外，您对实际像素数据的搜索假定它在位图标题之后立即开始。这很常见，但不是必需的。 file header包含实际像素数据的偏移量。（Microsoft文档将其称为“位图位”或“颜色数据”。）

我建议您对文件的开头执行十六进制转储，然后手动逐步执行，以确保所有偏移和假设都正确无误。您可以随意将十六进制转储的开头粘贴到您的问题中。

你在Windows上吗？你能打电话给LoadImage吗？

解码位图时获取不正确的宽度

1 个答案: