What is the case law on the Eighth Amendment ban on cruel and unusual punishment?

The Eighth Amendment ban on cruel and unusual punishment "flows from the basic ' "precept of justice that punishment for crime should be graduated and proportioned to [the] offense. [Citation.]" ' " ( Roper v. Simmons (2005) 543 U.S. 551, 560, 125 S.Ct. 1183, 161 L.Ed.2d 1 ( Roper ).) "By protecting even those convicted of heinous crimes, the Eighth Amendment reaffirms the duty of the government to respect the dignity of all persons." ( Ibid . ; see Robinson v. California (1962) 370 U.S. 660, 667, 82 S.Ct. 1417, 8 L.Ed.2d 758 [Eighth Amendment applies to the states].)