Let's say I have a sketch that interactively puts different fixed sizes shapes when I click with the mouse. I want this sketch to, in the end, save as a (let's say) 2000 x 1000 px image or svg. Problem is this is too big for my screen, so I'd like to actually view the window in a smaller size (say 1000 x 500 px) that would scale everything down proportionally, on this view, but would still output to 2000 x 1000 px (properly sized) in the end.

I'm looking for the best way to do this. I define “best” as being something that's both simple, and can be easily reused across different sketches, so it'd ideally be a few lines of code that I can just dump to a sketch, without having to change any other values in the sketch itself.

Yes, by exporting as an svg I could scale it later, but that would entail that I'd need to tell the sketch to draw every shape in half the size of what it is now, and that can become laborious.