Technically GUIs are, or used to be anyway, be drawn with drawing commands like "DrawRect, DrawLine, DrawRoundedBox", etc, which are basically vectors encoded i

Technically GUIs are, or used to be anyway, be drawn with drawing commands like "DrawRect, DrawLine, DrawRoundedBox", etc, which are basically vectors encoded in code and could be easily scaled. Windows has/had the metafile image file format[0] that basically encodes these calls into a stream for later reuse (AFAIK Office clip art used to be metafiles). Since these are vectors they can be arbitrarily scaled. The earlier versions of Windows even had to work not only on different pixel densities (that produced more or less the same visual screen space) but also on different pixel aspect ratios, like CGA's 640x200 mode. However once GUIs started relying on using bitmaps for drawing parts of the theme things got a bit less vector-y. But that happened later. [0] https://docs.microsoft.com/en-us/openspecs/windows_protocols/ms-wmf/ https://docs.microsoft.com/en-us/openspecs/windows_protocols...