void show_control(Control *c); void hide_control(Control *c); int is_visible(Control *c);
The show_control and hide_control functions make a control visible or invisible on its parent. The is_visible function returns zero if the control's state indicates it is not visible, or one if it is visible.
By default, controls are visible when they are created, but windows are not. Visibility is the quality of whether the control should be drawn if it is not obscured, not whether the control is currently unobscured.
A control might be visible, even if its parent window is not. Every object has its own visibility state, which is separate to every other object's state.