PRIMTIVE DA USARE IN ESERCIZIO 3
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PER COMODITA' LA DEFINIZIONE DI CIASCUNA PRIMITIVA E' STATA
INSERITA IN UNA FUNZIONE
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    /* Disegna parete piena = quadrato giacente su piano z=0 */
    void draw_wall()
    {
       gl.glBegin(GL.GL_QUADS);

       gl.glVertex3f(0.0f,0.0f,0.0f);
       gl.glVertex3f(1.0f,0.0f,0.0f);
       gl.glVertex3f(1.0f,1.0f,0.0f);
       gl.glVertex3f(0.0f,1.0f,0.0f);

       gl.glEnd();
    }

    /* Disegna parete forata = quadrato giacente su piano z=0 
       con al centro un foro quadrato, realizzata con striscia
       di 4 quadrilateri che girano attorno al buco */
    void draw_wall_with_hole()
    {
       gl.glBegin(GL.GL_QUAD_STRIP);
       
       gl.glVertex3f(0.0f,0.0f,0.0f);
       gl.glVertex3f(0.3f,0.3f,0.0f);

       gl.glVertex3f(1.0f,0.0f,0.0f);
       gl.glVertex3f(0.7f,0.3f,0.0f);

       gl.glVertex3f(1.0f,1.0f,0.0f);
       gl.glVertex3f(0.7f,0.7f,0.0f);

       gl.glVertex3f(0.0f,1.0f,0.0f);
       gl.glVertex3f(0.3f,0.7f,0.0f);

       gl.glVertex3f(0.0f,0.0f,0.0f);
       gl.glVertex3f(0.3f,0.3f,0.0f);

       gl.glEnd();
    }