A well known feature of Amiga is the ability to have multiple Intuition screens (ViewPorts in
graphics.library parlance) that coexist and can be laid out on the screen so that they overlap vertically. Additionally, the screen depth buttons allow one to reorder the priority of each screen, and also allows for a "screen switch" effect (if you keep all screens to the top).
This is possible because the generated video output parameters (resolution, where to fetch the bitplanes, color palette, etc...) can be reprogrammed at at any time, by virtue of the Copper.
By 1985, it was already expected for an OS to provide for multiplexed video output (i.e. the ability for different programs to have graphical output at the same time), but pretty much every other OS went with the idea of overlapping windows, and nobody provided the option of independent screens, not even a simple implementation where one could just switch between them.
who came up with the idea of multiple screens as a OS feature?
who came up with the idea of allowing screens to be dragged up and down?
could it be that the original idea was to give each program its own screen, and little to none widget toolkit, and Intuition and overlapping windows came at a later phase in the development of the machine? (by later phase I mean when it was already decided that Amiga would become a desktop computer).
(yes, I know that Dale Luck wrote the
graphics.library, but I'm wondering who took the final design decision to go with screen as a UI feature).