Set background image of an openGL window

Question

I am trying to set a background image of my openGL window by creating a quad on an orthogonal projection matrix and adding texture to it. I am also making use of GLUT toolkit in my application.

However I am having several problems. Below are screenshot illustrating the problem: image is grayscale and it repeats on x and y, even though texture size is set to be the same as the quad.

That is what I am trying to achieve:

And that is what I am getting:

Code for rendering and loading texture looks like this:

void orthogonalStart (void) {
    glMatrixMode(GL_PROJECTION);
    glPushMatrix();
    glLoadIdentity();
    gluOrtho2D(0, w1, 0, h1);
    glScalef(1, -1, 1);
    glTranslatef(0, -h1, 0);
    glMatrixMode(GL_MODELVIEW);
}

void orthogonalEnd (void) {
    glMatrixMode(GL_PROJECTION);
    glPopMatrix();
    glMatrixMode(GL_MODELVIEW);
}

GLuint LoadTexture( const char * filename, int width, int height )
{
    GLuint texture;
    unsigned char * data;
    FILE * file;

    //The following code will read in our RAW file
    file = fopen( filename, "rb" );
    if ( file == NULL ) return 0;
    data = (unsigned char *)malloc( width * height * 3 );
    fread( data, width * height * 3, 1, file );
    fclose( file );

    glGenTextures( 1, &texture ); 
    glBindTexture( GL_TEXTURE_2D, texture ); 
    glTexEnvf( GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_MODULATE ); 


    //even better quality, but this will do for now.
    glTexParameterf( GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER,GL_LINEAR );
    glTexParameterf( GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER,GL_LINEAR );


    //to the edge of our shape. 
    glTexParameterf( GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT );
    glTexParameterf( GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT );

    //Generate the texture
    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, width, height, 0,GL_RGB, GL_UNSIGNED_BYTE, data);
    free( data ); //free the texture
    return texture; //return whether it was successful
}

void FreeTexture( GLuint texture )
{
  glDeleteTextures( 1, &texture );
}

void background (void) {
    glBindTexture( GL_TEXTURE_2D, texture ); 

    orthogonalStart();

    glBegin(GL_QUADS);
        glTexCoord2d(0.0,0.0); glVertex2f(0, 0);
        glTexCoord2d(1.0,0.0); glVertex2f(1024, 0);
        glTexCoord2d(1.0,1.0); glVertex2f(1024, 1024);
        glTexCoord2d(0.0,1.0); glVertex2f(0, 1024);
        glEnd();

    orthogonalEnd();
}

void display (void) {
    glClearColor (1.0,0.0,0.0,1.0);
    glClear (GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    glLoadIdentity();
    glEnable( GL_TEXTURE_2D );

    background();
    gluLookAt (0.0, 0.0, 5.0, 0.0, 0.0, 0.0, 0.0, 1.0, 0.0);

    glutSwapBuffers();
}

To convert texture from png into Raw format I use photoshop, so I thought greyscale image might be due to conversion.

Note: I have just started learning open, so this might be not the best approach. Please let me know if there is a better way

Edit: Image has to stay on one place and not rescalse

Answer 1

I'd avoid doing anything other than a glFrustum() or glOrtho() call for your projection matrix.

Also, set GL_UNPACK_ALIGNMENT to 1 for your texture loading if you're doing 3-component pixels:

#include <GL/glut.h>

int w1 = 0;
int h1 = 0;
void reshape(int w, int h)
{
    w1 = w;
    h1 = h;
    glViewport(0, 0, w, h);
}


void orthogonalStart() 
{
    glMatrixMode(GL_PROJECTION);
    glPushMatrix();
    glLoadIdentity();
    gluOrtho2D(-w1/2, w1/2, -h1/2, h1/2);
    glMatrixMode(GL_MODELVIEW);
}

void orthogonalEnd()
{
    glMatrixMode(GL_PROJECTION);
    glPopMatrix();
    glMatrixMode(GL_MODELVIEW);
}


GLuint texture = 0;
void background()
{
    glBindTexture( GL_TEXTURE_2D, texture ); 

    orthogonalStart();

    // texture width/height
    const int iw = 500;
    const int ih = 500;

    glPushMatrix();
    glTranslatef( -iw/2, -ih/2, 0 );
    glBegin(GL_QUADS);
        glTexCoord2i(0,0); glVertex2i(0, 0);
        glTexCoord2i(1,0); glVertex2i(iw, 0);
        glTexCoord2i(1,1); glVertex2i(iw, ih);
        glTexCoord2i(0,1); glVertex2i(0, ih);
    glEnd();
    glPopMatrix();

    orthogonalEnd();
}


void display()
{
    glClearColor (1.0,0.0,0.0,1.0);
    glClear (GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    glLoadIdentity();
    glEnable( GL_TEXTURE_2D );

    background();
    gluLookAt (0.0, 0.0, 5.0, 0.0, 0.0, 0.0, 0.0, 1.0, 0.0);

    glutSwapBuffers();
}


GLuint LoadTexture()
{
    unsigned char data[] = { 255,0,0, 0,255,0, 0,0,255, 255,255,255 };

    glGenTextures( 1, &texture ); 
    glBindTexture( GL_TEXTURE_2D, texture ); 
    glPixelStorei( GL_UNPACK_ALIGNMENT, 1 );
    glTexEnvf( GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_MODULATE ); 

    //even better quality, but this will do for now.
    glTexParameterf( GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER,GL_NEAREST);
    glTexParameterf( GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER,GL_NEAREST);

    //to the edge of our shape. 
    glTexParameterf( GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT );
    glTexParameterf( GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT );

    //Generate the texture
    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, 2, 2, 0,GL_RGB, GL_UNSIGNED_BYTE, data);
    return texture; //return whether it was successful
}


int main(int argc, char **argv)
{
    glutInit(&argc, argv);
    glutInitDisplayMode(GLUT_RGBA | GLUT_DEPTH | GLUT_DOUBLE);

    glutInitWindowSize(800,600);
    glutCreateWindow("Aspect Ratio");

    glutDisplayFunc(display);
    glutReshapeFunc(reshape);
    texture = LoadTexture();
    glutMainLoop();
    return 0;
}