How have courts interpreted qualified immunity in civil cases?

"Qualified immunity is applicable unless the official's conduct violated a clearly established constitutional right." Pearson, 555 U.S. at 232. To be "clearly established" "[t]he contours of the right must be sufficiently clear that a reasonable official would understand that what he is doing violates that right." Anderson v. Creighton, 483 U.S. 635, 640 (1987). "This is not to say that an official action is protected by qualified immunity unless the very action in question has previously been held unlawful, but it is to say that in light of pre-existing law the unlawfulness must be apparent." Id.