How to load texture 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;                                   
}

You should try to look at using shaders. These calls are somewhat dated, and might cause some trouble if you try to draw more varied — Charlie
– Charlie, Commented Jan 25, 2017 at 18:05
Get a different resource. The code violates effective type rule, and invokes undefined behaviour. — too honest for this site
– too honest for this site, Commented Jan 25, 2017 at 18:09
@Charlie : What are shaders ? I never worked with shaders before. Could you please suggest me any tutorial ? — Luatic
– Luatic, Commented Jan 25, 2017 at 18:18
opengl-tutorial.org/beginners-tutorials/… halfway down the page. A shader is basically a way to send tasks to the GPU itself, instead of doing everyting on the CPU. Its very effective, and necessary even — Charlie
– Charlie, Commented Jan 25, 2017 at 19:52

lmat - Reinstate Monica · Accepted Answer · 2021-12-03 12:31:56Z

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;
}

Ripi2 · Accepted Answer · 2017-01-25 18:04:15Z

1

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 datainstead of dataPos.

answered Jan 25, 2017 at 18:04

Ripi2

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14 Comments

Luatic Over a year ago

Ok, ill watch out, but why is the previous set color used, why isnt it white ?

Ripi2 Over a year ago

A texture is nothing but a buffer. It needs to be filled with something. I don't know if pyopengl sets a default color. Because your glTexImage2D doesn't work the buffer is undefined. Only quads are drawn in the current color, red in your case.

Luatic Over a year ago

Thanks , thats useful to me . Ill try it out.

Luatic Over a year ago

Could you please show me how to load and use a texture correctly ? Nothing worked for me. Please link me a tutorial or something else that helps me to get this to work.

Luatic Over a year ago

I have worked with textures in pyopengl. Its really easy. But in c, I have no working idea about how to load an image. Could you please have a look at my new code ? Why doesnt it work ?

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