Joseph Kosinski and Claudio Miranda didn't like the extensive use of blue screen mattes in TRON: Legacy (2010) to such an extent, that for this film, they wanted to use real glass, mirrors and shiny surfaces for the glass tower set.
The sky footage was projected on a 500 by 45 feet screen consisting of 21 monitors taken from three weeks of footage from the summit of Haleakala volcano in Maui, Hawaii. The rooms with windows were lit by the light from those projections.
The monitors took ten technicians several weeks to install and fine tune with floor-level rig support. In the end, it had the actors complimenting the production team for that set design that, as such, Tom Cruise declared that the glass tower was one of his favorite film sets.