Question

I am loading bitmap file and creating texture this way:

LoadBitmapFromFile( "img.bmp", &bitmapFile );

glGenTextures(1, &texture[0] );
glBindTexture(GL_TEXTURE_2D, texture[0] );


glTexImage2D(GL_TEXTURE_2D, 0, 3, bitmapFile.width, bitmapFile.height, 0, GL_RGB, GL_UNSIGNED_BYTE, bitmapFile.data);


glTexEnvf( GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_MODULATE );

glTexParameterf( GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER,
                 GL_LINEAR_MIPMAP_NEAREST );

glTexParameterf( GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR );

glTexParameterf( GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT );
glTexParameterf( GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT );

Later on, I try to texture triangles:

glEnable( GL_TEXTURE_2D );
        glPushMatrix();
            glBindTexture( GL_TEXTURE_2D, texture[0] );
            glBegin( GL_TRIANGLE_STRIP );
                glTexCoord2f( 0, 0 ); glVertex2f( 0, 768 );
                glTexCoord2f( 1, 0 ); glVertex2f( 1024, 768 );
                glTexCoord2f( 1, 1 ); glVertex2f( 0, 0 );
                glTexCoord2f( 0, 1 ); glVertex2f( 1024, 0 );
            glEnd();
        glPopMatrix();
    glDisable( GL_TEXTURE_2D );

But texture doesn’t show on screen, other coloured primitives do.

It does work with glDrawPixel, but doesn’t texture triangles, what could be wrong?

I have simplified my app just to show the problem:
(also had to include glext, as it didn’t found GL_CLAMP_TO_EDGE)

#include <GL/glfw.h>
#include <fstream>
#include <cstdlib>
#include "glext.h"

typedef struct BitmapFile
{
    int width, height;
    unsigned char* data;
};

BitmapFile bitmapFile;

GLuint texture[1];

void LoadBitmapFromFile( char *filename, BitmapFile *bitmap )
{
    int bitmapSize = 0;
    int i = 0;

    FILE *file;

    file = fopen( filename, "rb" );
    if( !file )
    {
        fclose(file);
        return;
    }

    fseek(file, 18, SEEK_SET);
    fread(&bitmap->width, 4, 1, file);

    fseek(file, 22, SEEK_SET);
    fread(&bitmap->height, 4, 1, file);

    fseek(file, 34, SEEK_SET);
    fread(&bitmapSize, 4, 1, file);

    bitmap->data = (unsigned char*)malloc(bitmapSize);
    fseek(file, 54, SEEK_SET);
    fread(bitmap->data, bitmapSize, 1, file);

    for( i = 0; i < bitmapSize; i+=3 )
    {
        int tempByte = bitmap->data[i];
        bitmap->data[i] = bitmap->data[i+2];
        bitmap->data[i+2] = tempByte;
    }

    fclose(file);
}

int LoadGLTextures()                                  
{
    LoadBitmapFromFile( "img.bmp", &bitmapFile );

    glGenTextures(1, &texture[0] );
    glBindTexture(GL_TEXTURE_2D, texture[0] );


    glTexImage2D(GL_TEXTURE_2D, 0, 3, bitmapFile.width, bitmapFile.height, 0, GL_RGB, GL_UNSIGNED_BYTE, bitmapFile.data);


    glTexEnvf( GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_MODULATE );

    /*glTexParameterf( GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER,
                     GL_LINEAR_MIPMAP_NEAREST );

    glTexParameterf( GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR );*/
    glTexParameterf( GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);


    glTexParameterf( GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE ); 
    glTexParameterf( GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE );

    return true;
}

int main()
{
    glfwInit();

    glEnable( GL_TEXTURE_2D );
    glShadeModel( GL_SMOOTH );

    LoadGLTextures();

    glfwOpenWindowHint( GLFW_WINDOW_NO_RESIZE, GL_TRUE );
    glfwOpenWindow( 1024, 768, 0, 0, 255, 0, 32, 0, GLFW_WINDOW );


    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    glOrtho(0.0, 1024, 768, 0, -1.0, 1.0); 
    glMatrixMode( GL_MODELVIEW );

    while( !glfwGetKey( GLFW_KEY_ESC ) )
    {
        glClearColor(0.0, 1.0, 1.0, 0.0);
        glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

        glBindTexture( GL_TEXTURE_2D, texture[0] );
        glPushMatrix();

            glBegin( GL_TRIANGLE_STRIP );
                glTexCoord2f( 0, 0 ); glVertex2f( 0, 768 );
                glTexCoord2f( 1, 0 ); glVertex2f( 1024, 768 );
                glTexCoord2f( 1, 1 ); glVertex2f( 0, 0 );
                glTexCoord2f( 0, 1 ); glVertex2f( 1024, 0 );
            glEnd();
        glPopMatrix();

        glDrawPixels( bitmapFile.width, bitmapFile.height, GL_RGB, GL_UNSIGNED_BYTE, bitmapFile.data);

        glfwSwapBuffers();
        glFlush();
    }

    glfwTerminate();
}

http://imageshack.us/photo/my-images/254/89567090.jpg/

---

Ok, I’m powerless, after last changes loading function looks like that:

int LoadGLTextures()                                  
{
    LoadBitmapFromFile( "img.bmp", &bitmapFile );

    glGenTextures(1, &texture[0] );
    glBindTexture(GL_TEXTURE_2D, texture[0] );

    //glGenerateMipmap(GL_TEXTURE_2D);
    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, bitmapFile.width, bitmapFile.height, 0, GL_RGB, GL_UNSIGNED_BYTE, bitmapFile.data);

    for( int i = 0 ; i < 8 ; i++ )
    {
        glTexImage2D(GL_TEXTURE_2D, i+1, GL_RGB, bitmapFile.width/(2*(i+1)), bitmapFile.height/(2*(i+1)), 0, GL_RGB, GL_UNSIGNED_BYTE, bitmapFile.data);
    }

    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR_MIPMAP_LINEAR);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR_MIPMAP_LINEAR);
    return true;
}

But on screen there are still no changes.
( bitmap is 256×256 )

Answer 1

You’re loading only one level but enable mipmaping by calling

glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR_MIPMAP_NEAREST);

If loading only one level you must disable mipmaping with

glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);

or

glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);

Update due to having seen the code:

The OP tried to load textures before a OpenGL context was available.