Block 1:
   glBegin(GL_TRIANGLES);
      glColor3f(1.0, 0.0, 0.0);
      glVertex3f(20.0, 20.0, 0.0);
      glColor3f(0.0, 1.0, 0.0);
      glVertex3f(80.0, 20.0, 0.0);
      glColor3f(0.0, 0.0, 1.0);
      glVertex3f(80.0, 80.0, 0.0);
   glEnd();

Block 2:
   glBegin(GL_TRIANGLES);
      glColor3f(1.0, 0.0, 0.0);
      glVertex3f(20.0, 20.0, 0.0);
      glColor3f(0.0, 1.0, 0.0);
      glVertex3f(80.0, 20.0, 0.0);
      glColor3f(0.0, 0.0, 1.0);
      glVertex3f(80.0, 80.0, 0.0);
   glEnd();