3d cube opengl - overlapping sides

Question

I want to create a 3d cube with openGL. Also, I want to cover each side with an image that I transform in a texture.

I find cube coordinates in 2D, and I create a QUADS for each side.

My problem is that when I render textures corresponding cube sides, I see these textures overlap each other, as you can see in this image:

enter image description here

my code is:

Initialization:

glGenTextures(2, textures);
glClearColor (0.0, 0.0, 0.0, 0.0);
glClearDepth(1.0f);                         // Depth Buffer Setup
glEnable(GL_DEPTH_TEST);                        // Enables Depth Testing
glDepthFunc(GL_ALWAYS);

Transform image in thexture:

up = imread("up.png");

glHint(GL_PERSPECTIVE_CORRECTION_HINT,GL_NICEST);
    glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
    glBindTexture(GL_TEXTURE_2D, textures[1]);
    glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MIN_FILTER,GL_LINEAR);
    glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MAG_FILTER,GL_LINEAR);
    gluBuild2DMipmaps(GL_TEXTURE_2D, GL_RGB, up.cols, up.rows, GL_RGB, GL_UNSIGNED_BYTE, up.data);

Display cube:

glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    glEnable(GL_TEXTURE_2D);

    // Set Projection Matrix
    glMatrixMode (GL_PROJECTION);
    glLoadIdentity();
    gluOrtho2D(0, WIDTH, HEIGHT, 0); 

    // Switch to Model View Matrix
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity(); 

glBindTexture(GL_TEXTURE_2D, textures[1]);
        glBegin(GL_QUADS);
        //sopra
        glTexCoord2f(0.0f, 0.0f); glVertex2f((GLfloat)((coord[6].x)),(GLfloat)(coord[6].y));
        glTexCoord2f(1.0f, 0.0f); glVertex2f((GLfloat)((coord[5].x)),(GLfloat)(coord[5].y));
        glTexCoord2f(1.0f, 1.0f); glVertex2f((GLfloat)((coord[4].x)),(GLfloat)(coord[4].y));
        glTexCoord2f(0.0f, 1.0f); glVertex2f((GLfloat)((coord[7].x)),(GLfloat)(coord[7].y)); 
        glEnd();

I do the same for the other sides of the cube. The order in which I render textures is:

bottom (ground) side

up side

behind side

front side

left side

right side

what is wrong or what am I missing? Or, Maybe cannot create a 3d cube with 2d coordinates (glVertex2f (...))?

Thanks for your help!

Why don't you use regular 3D object instead of faking it in 2D? It messes up your depth buffer and distorts your texture. — Matzi
@Matzi because I'm able to find 2d coordinates... I don't know how to find 3d coordinates.. — Cristina1986

David Saxon David Saxon · Accepted Answer · 2013-02-18T23:36:19

You can't create a cube with 2d coordinates. The sides are overlapping because they are all on the same plane in space. A cube is in 3d space so needs 3 coordinates, x, y, and z.

So try using:

glVertex3f(x, y, z);

and use some appropriate z values depending on where you want each face.

For the texture you can still use:

glTexCoord2f(x, y);

since the textures are in 2 dimensional space.

If you are still confused about what to use for your coordinates I suggest you read this to help you understand 3d space in openGL:

http://www.falloutsoftware.com/tutorials/gl/gl0.htm

3d cube opengl - overlapping sides

1 Answers