Light and privacy in la Pedrera, by Gaudí 
Gaudí was forced by the circumstances of the moment to use the roller shutters in la Pedrera. Some earlier buildings, as Lleó house (Domenech) and the Quadras house (Puig), had introduced it. Customers were unwilling to open the window to move the exterior shutters.
But the roller shutters, as opening from the bottom to the top, made the bedrooms lose all the privacy when seeking some light. Perhaps that is why Gaudí decided to fragment the enclosure placing two shutters: a short one that opened only the skylight on the top, and a long one passing in front of it and covering the rest of the window. Furthermore, in this second shutter, the guide could be projected to see the patio.
So Gaudí got that the room could be illuminated without losing privacy, opening only the upper shutter. If, in addition, the lower was projected, when closed, the bedroom could have light and views without the interior of it being visible from the opposite window.