Images in Photoshop
Update March 2017: Photoshop CC 2017 on macOS 10.12 has developed new behavior such that 2:1 scaling works correctly but other scaling ratios can look just horribly blurred (on any display).
Theses screen shots show what it is like to view an image in Photoshop using display scaling of 2048 X 1080.
Photoshop always draws to full screen resolution regardless of the display scaling (which applies to user interface elements).
Three zoom sizes are shown (toggle).