Question

Is there a way to draw a cube like this and as a result, only upload 8 verticies and 24 indicies to the graphics card? If so how could this be done?

Thanks

I currently do it like this:

boxdims.x = w;
    boxdims.y = h;
    boxdims.z = d;
    center = c;

    GLfloat vboverticies[72];
    GLfloat vbonormals[18];
    Vertex3f verticies[24];

    //Top face
    verticies[0] = Vertex3f(-boxdims.x / 2.0f,boxdims.y / 2.0f, -boxdims.z / 2.0f);
    verticies[1] = Vertex3f(-boxdims.x / 2.0f,boxdims.y / 2.0f, boxdims.z / 2.0f);
    verticies[2] = Vertex3f(boxdims.x / 2.0f,boxdims.y / 2.0f, boxdims.z / 2.0f);
    verticies[3] = Vertex3f(boxdims.x / 2.0f,boxdims.y / 2.0f, -boxdims.z / 2.0f);


    //Bottom face
    verticies[4] = Vertex3f(-boxdims.x / 2.0f,-boxdims.y / 2.0f, -boxdims.z / 2.0f);
    verticies[5] = Vertex3f(boxdims.x / 2.0f,-boxdims.y / 2.0f, -boxdims.z / 2.0f);
    verticies[6] = Vertex3f(boxdims.x / 2.0f,-boxdims.y / 2.0f, boxdims.z / 2.0f);
    verticies[7] = Vertex3f(-boxdims.x / 2.0f,-boxdims.y / 2.0f, boxdims.z / 2.0f);


    //Left face
    verticies[8] = Vertex3f(-boxdims.x / 2.0f,-boxdims.y / 2.0f, -boxdims.z / 2.0f);
    verticies[9] = Vertex3f(-boxdims.x / 2.0f,-boxdims.y / 2.0f, boxdims.z / 2.0f);
    verticies[10] =Vertex3f(-boxdims.x / 2.0f,boxdims.y / 2.0f, boxdims.z / 2.0f);
    verticies[11] =Vertex3f(-boxdims.x / 2.0f,boxdims.y / 2.0f, -boxdims.z / 2.0f);


    //Right face
    verticies[12] =Vertex3f(boxdims.x / 2.0f,-boxdims.y / 2.0f, -boxdims.z / 2.0f);
    verticies[13] =Vertex3f(boxdims.x / 2.0f,boxdims.y / 2.0f, -boxdims.z / 2.0f);
    verticies[14] =Vertex3f(boxdims.x / 2.0f,boxdims.y / 2.0f, boxdims.z / 2.0f);
    verticies[15] =Vertex3f(boxdims.x / 2.0f,-boxdims.y / 2.0f, boxdims.z / 2.0f);

    //Front face
    verticies[16] =Vertex3f(-boxdims.x / 2.0f,-boxdims.y / 2.0f, boxdims.z / 2.0f);
    verticies[17] =Vertex3f(boxdims.x / 2.0f,-boxdims.y / 2.0f, boxdims.z / 2.0f);
    verticies[18] =Vertex3f(boxdims.x / 2.0f,boxdims.y / 2.0f, boxdims.z / 2.0f);
    verticies[19] =Vertex3f(-boxdims.x / 2.0f,boxdims.y / 2.0f, boxdims.z / 2.0f);

    //Back face
    verticies[20] =Vertex3f(-boxdims.x / 2.0f,-boxdims.y / 2.0f, -boxdims.z / 2.0f);
    verticies[21] =Vertex3f(-boxdims.x / 2.0f,boxdims.y / 2.0f, -boxdims.z / 2.0f);
    verticies[22] =Vertex3f(boxdims.x / 2.0f,boxdims.y / 2.0f, -boxdims.z / 2.0f);
    verticies[23] =Vertex3f(boxdims.x / 2.0f,-boxdims.y / 2.0f, -boxdims.z / 2.0f);




    for(int i = 0; i < 24; i++)
    {
        verticies[i].x += center.x;
        verticies[i].y += center.y;
        verticies[i].z += center.z;
    }


    int count = 0;
    for(int i = 0; i < 24; ++i)
    {
        vboverticies[count] = verticies[i].x;
        count++;
        vboverticies[count] = verticies[i].y;
        count++;
        vboverticies[count] = verticies[i].z;
        count++;
    }

    //glNormal3f(0.0, 1.0f, 0.0f);
    //glNormal3f(0.0, -1.0f, 0.0f);
    //glNormal3f(-1.0, 0.0f, 0.0f);
    //glNormal3f(1.0, 0.0f, 0.0f);
    //glNormal3f(0.0, 0.0f, 1.0f);
    //glNormal3f(0.0, 0.0f, -1.0f);
    vbonormals[0] = (0.0);
    vbonormals[1] = (1.0);
    vbonormals[2] = (0.0);

    vbonormals[3] = (0.0);
    vbonormals[4] = (-1.0);
    vbonormals[5] = (0.0);

    vbonormals[6] = (-1.0);
    vbonormals[7] = (0.0);
    vbonormals[8] = (0.0);

    vbonormals[9] = (1.0);
    vbonormals[10]= (0.0);
    vbonormals[11]= (0.0);

    vbonormals[12]= (0.0);
    vbonormals[13]= (0.0);
    vbonormals[14]= (1.0);

    vbonormals[15]= (0.0);
    vbonormals[16]= (0.0);
    vbonormals[17]= (-1.0);



    //Create the VBO
    glDeleteBuffers(1, &vboID);
    glGenBuffersARB(1, &vboID);
    glBindBufferARB(GL_ARRAY_BUFFER, vboID);
    glBufferDataARB(GL_ARRAY_BUFFER, (72 * sizeof(GLfloat)) + 
        (18 * sizeof(GLfloat)) , NULL, GL_STATIC_COPY);

    glBufferSubDataARB(GL_ARRAY_BUFFER_ARB, 0, 72 * sizeof(GLfloat), vboverticies);
    glBufferSubDataARB(GL_ARRAY_BUFFER_ARB, 72 * sizeof(GLfloat),
        18 * sizeof(GLfloat), vbonormals);


}

Answer 1

The answer is no.

If you need normals, you’ll have to have 24 vertices, as no face shares normals. Note that the example provided by shk does not handle normals.