1) What are the differences between "scaling mode centered" and "scaling mode, centered keep aspect ratio"?
For each resolution selcted (640x480,2560x1440 or above my native resolution or other (my display is 2560x1440)), with "centered", aspect ratio stay 4/3.
With "centered keep aspect ratio", aspect ratio stay 4/3 if I select 4/3 resolution under my native resolution but if I select 16/9 resolution, aspect ratio become 16/9. If I select resolution above my native resolution, it's zoomed.
for example:
my native resolution : 2560x1440 (16/9)
croc "centered keep aspect ratio" at 3840x2880 (4/3 resolution)
image is zoomed
croc "with centered", "stretched keep aspect ratio" or "stretched 4/3 aspect ratio" at 3840x2880 (4/3 resolution)
aspect ratio stay 4/3
croc with "centered", "stretched keep aspect ratio" or "stretched 4/3 aspect ratio" or "centered keep aspect ratio" at 1920x1440
aspect ratio stay 4/3
croc with "centered", at 2560x1440, aspect ratio stay 4/3
croc with "stretched keep aspect ratio" or "stretched 4/3 aspect ratio" or "centered keep aspect ratio" at 2560x1440
aspect ratio is 16/9
croc "centered keep aspect ratio" at 3840x2160 (16/9 resolution)
image is zoomed
croc with "centered", at 3840x2160 , aspect ratio stay 4/3
croc with "stretched keep aspect ratio" or "stretched 4/3 aspect ratio" at 3840x2160
aspect ratio is 16/9