> Well, [throwing away the complete rendered graphics] is what "retained mode" GUIs (i.e. those using control/widget trees and such) do too.

That turns out not to be the case.

The widget tree is retained.

When changes come in, the resulting damage from those changes is assessed and then the damaged parts are redrawn in an optimized fashion.

https://developer.apple.com/documentation/AppKit/NSView/draw...