如何加载纹理Opengl？

Question

I found a useful post at this site, where some code is used to load a BMP This code should load the header, read out infos, go further, read data, generate texture and bin it. But it doesnt work. What am I doing wrong ?

Texture Declaration :

GLuint texture[1];

BMP Loading :

void LoadTexture(char *filename)
{
    FILE * file = fopen(filename,"rb");

    unsigned char header[54];
    unsigned int dataPos;
    unsigned int imageSize;
    unsigned int width, height;

    fread(header,1,54,file);

    dataPos    = *(int*)&(header[0x0A]);
    imageSize  = *(int*)&(header[0x22]);
    width      = *(int*)&(header[0x12]);
    height     = *(int*)&(header[0x16]);

    if (imageSize==0) {
        imageSize=width*height*3; 
        }
    if (dataPos==0) {
        dataPos=54; 
    }
    unsigned char data[imageSize];
    fseek(file, SEEK_SET, 53);
    fread(data,1,imageSize,file);

    fclose(file);

    glActiveTexture(GL_TEXTURE1);

    glGenTextures(1, texture[0]);

    glBindTexture(GL_TEXTURE_2D, texture[0]);

    glTexImage2D(GL_TEXTURE_2D, 0,GL_RGB, width, height, 0, GL_BGR, GL_UNSIGNED_BYTE, data);

    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);

    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR_MIPMAP_LINEAR);

    glGenerateMipmap(GL_TEXTURE_2D);

    glBindTexture(GL_TEXTURE_2D, texture[0]);
}

EDIT : I printed out some values read from the header. The header seems to be read properly.

Drawing :

int DrawGLScene(GLvoid)                         
{   
    glLoadIdentity();
        glEnable(GL_TEXTURE_2D);                        
    glTranslatef(0.0f,0.0f,-5.0f);
        glActiveTexture(GL_TEXTURE1);
    glBindTexture(GL_TEXTURE_2D, texture[0]);

    glBegin(GL_QUADS);

        glTexCoord2f(0.0f, 0.0f); glVertex3f(-1.0f, -1.0f,  1.0f);
        glTexCoord2f(1.0f, 0.0f); glVertex3f( 1.0f, -1.0f,  1.0f);
        glTexCoord2f(1.0f, 1.0f); glVertex3f( 1.0f,  1.0f,  1.0f);
        glTexCoord2f(0.0f, 1.0f); glVertex3f(-1.0f,  1.0f,  1.0f);

        glTexCoord2f(1.0f, 0.0f); glVertex3f(-1.0f, -1.0f, -1.0f);
        glTexCoord2f(1.0f, 1.0f); glVertex3f(-1.0f,  1.0f, -1.0f);
        glTexCoord2f(0.0f, 1.0f); glVertex3f( 1.0f,  1.0f, -1.0f);
        glTexCoord2f(0.0f, 0.0f); glVertex3f( 1.0f, -1.0f, -1.0f);

        glTexCoord2f(0.0f, 1.0f); glVertex3f(-1.0f,  1.0f, -1.0f);
        glTexCoord2f(0.0f, 0.0f); glVertex3f(-1.0f,  1.0f,  1.0f);
        glTexCoord2f(1.0f, 0.0f); glVertex3f( 1.0f,  1.0f,  1.0f);
        glTexCoord2f(1.0f, 1.0f); glVertex3f( 1.0f,  1.0f, -1.0f);

        glTexCoord2f(1.0f, 1.0f); glVertex3f(-1.0f, -1.0f, -1.0f);
        glTexCoord2f(0.0f, 1.0f); glVertex3f( 1.0f, -1.0f, -1.0f);
        glTexCoord2f(0.0f, 0.0f); glVertex3f( 1.0f, -1.0f,  1.0f);
        glTexCoord2f(1.0f, 0.0f); glVertex3f(-1.0f, -1.0f,  1.0f);

        glTexCoord2f(1.0f, 0.0f); glVertex3f( 1.0f, -1.0f, -1.0f);
        glTexCoord2f(1.0f, 1.0f); glVertex3f( 1.0f,  1.0f, -1.0f);
        glTexCoord2f(0.0f, 1.0f); glVertex3f( 1.0f,  1.0f,  1.0f);
        glTexCoord2f(0.0f, 0.0f); glVertex3f( 1.0f, -1.0f,  1.0f);

        glTexCoord2f(0.0f, 0.0f); glVertex3f(-1.0f, -1.0f, -1.0f);
        glTexCoord2f(1.0f, 0.0f); glVertex3f(-1.0f, -1.0f,  1.0f);
        glTexCoord2f(1.0f, 1.0f); glVertex3f(-1.0f,  1.0f,  1.0f);
        glTexCoord2f(0.0f, 1.0f); glVertex3f(-1.0f,  1.0f, -1.0f);
    glEnd();
    glFlush();
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    return 1;                                   
}

Answer 1

Finally, after browsing the internet quite a lot, I found this working example :

#include <stdlib.h>
#include <string.h>
#include <GL/glut.h>
#include <GL/gl.h>
#include <GL/glu.h>
#include <stdio.h>
#include <math.h>

GLuint texture[2];


struct Image {

    unsigned long sizeX;

    unsigned long sizeY;

    char *data;

};

typedef struct Image Image;


#define checkImageWidth 64

#define checkImageHeight 64


GLubyte checkImage[checkImageWidth][checkImageHeight][3];

void makeCheckImage(void){

    int i, j, c;

    for (i = 0; i < checkImageWidth; i++) {

        for (j = 0; j < checkImageHeight; j++) {

            c = ((((i&0x8)==0)^((j&0x8)==0)))*255;

            checkImage[i][j][0] = (GLubyte) c;

            checkImage[i][j][1] = (GLubyte) c;

            checkImage[i][j][2] = (GLubyte) c;

        }

    }

}



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("File 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 bitsperpixel

    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");

        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 1;

}


Image * loadTexture(){

    Image *image1;

    // allocate space for texture

    image1 = (Image *) malloc(sizeof(Image));

    if (image1 == NULL) {

        printf("Error allocating space for image");

        exit(0);

    }

    if (!ImageLoad("NeHe.bmp", image1)) {

        exit(1);

    }

    return image1;

}



void myinit(void)

{

    glClearColor (0.5, 0.5, 0.5, 0.0);

    glEnable(GL_DEPTH_TEST);

    glDepthFunc(GL_LESS);

    Image *image1 = loadTexture();

    if(image1 == NULL){

        printf("Image was not returned from loadTexture\n");

        exit(0);

    }

    makeCheckImage();

    glPixelStorei(GL_UNPACK_ALIGNMENT, 1);

    // Create Texture

    glGenTextures(2, texture);

    glBindTexture(GL_TEXTURE_2D, texture[0]);

    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

    glTexImage2D(GL_TEXTURE_2D, 0, 3, image1->sizeX, image1->sizeY, 0,

    GL_RGB, GL_UNSIGNED_BYTE, image1->data);

    glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_DECAL);

    glBindTexture(GL_TEXTURE_2D, texture[1]);

    glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP);

    glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP);

    glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);

    glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);

    glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_DECAL);

    glTexImage2D(GL_TEXTURE_2D, 0, 3, checkImageWidth,

    checkImageHeight, 0, GL_RGB, GL_UNSIGNED_BYTE,&checkImage[0][0][0]);

    glEnable(GL_TEXTURE_2D);

    glShadeModel(GL_FLAT);

}



void display(void){

    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

    glBindTexture(GL_TEXTURE_2D, texture[1]);

    glutSolidTeapot(1.0);

    glBindTexture(GL_TEXTURE_2D, texture[0]);

    glBegin(GL_QUADS);

    glTexCoord2f(0.0, 0.0);

    glVertex3f(1.0, -1.0, 0.0);

    glTexCoord2f(1.0, 0.0);

    glVertex3f(1.0, 1.0, 0.0);

    glTexCoord2f(1.0, 1.0);

    glVertex3f(2.41421, 1.0, -1.41421);

    glTexCoord2f(0.0, 1.0);

    glVertex3f(2.41421, -1.0, -1.41421);

    glEnd();

    glutSwapBuffers();

}


void myReshape(int w, int h){

    glViewport(0, 0, w, h);

    glMatrixMode(GL_PROJECTION);

    glLoadIdentity();

    gluPerspective(60.0, 1.0*(GLfloat)w/(GLfloat)h, 1.0, 30.0);

    glMatrixMode(GL_MODELVIEW);

    glLoadIdentity();

    glTranslatef(0.0, 0.0, -3.6);

}


void keyboard (unsigned char key, int x, int y){

    switch (key) {

        case 27: // “esc” on keyboard

        exit(0);

        break;

        default: // “a” on keyboard

        break;

    }

}


int main(int argc, char** argv)

{

    glutInit(&argc, argv);

    glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB | GLUT_DEPTH);

    glutCreateWindow("Texture Mapping - Programming Techniques");

    myinit();

    glutReshapeFunc (myReshape);

    glutDisplayFunc(display);

    glutKeyboardFunc(keyboard);

    glutMainLoop();

    return 0;

}

Answer 2

Review how you read data. dataPos , size and others may be set after reading the BMP. It's a relative position defined in the header of the image file.

And then review glTexImage2D(). Your are passing data instead of dataPos .