Windows Aero

Windows Aero shipped with Windows Vista in 2007 and reached its best-liked form in Windows 7 in 2009. The signature is the window frame: a thick title bar and border made of translucent glass, blurring whatever happens to be behind it in real time, tinted with a colour the user picked, edged with a bright inner highlight, and rounded at the top corners. Around that sat the rest of the kit, a soft outer glow instead of a hard drop shadow, oversized window controls with their own glass pills, live thumbnails in the taskbar, and animated window transitions including the notorious Flip 3D. It needed a GPU, which is exactly why Microsoft dropped most of it in Windows 8 and why the tablets of the period never got it.

Set it against Mica and the whole argument becomes visible. Aero blurs whatever is behind the window, continuously, and tints the result, so dragging a window across the desktop changes what its own frame looks like, frame by frame. Mica samples the desktop wallpaper once, tints an opaque surface with it, and never looks again, so moving the window changes nothing and only a wallpaper change does. That is not a small implementation detail: Mica is deliberately the cheap version, designed after a decade of complaints about battery and compositor cost, and it is the reason the effect could come back at all. Aero is glass, Mica is a painted wall that happens to match the room.

The other useful comparison is Aqua, Apple’s contemporary. Both are glossy and both lean on translucency, but Aqua’s gloss is a material applied to controls, with candy buttons and pinstripes and a lozenge scrollbar, whereas Aero left the controls comparatively plain and spent its whole effect on the window frame.

For a modern reader the useful word is glassmorphism, which is the same technique generalized and given a CSS property. Aero was a compositor feature nobody on the web could have; backdrop-filter is that feature, available in a stylesheet, and the lessons Aero learned the hard way transfer directly. Text on glass fails contrast the moment the wallpaper changes, so the tint has to be opaque enough to guarantee a floor rather than merely look good over the developer’s own desktop. Blur is expensive to composite, and a page that blurs a large area on every scroll frame will feel it. And a see-through frame is a decision about what the user is meant to attend to: Aero’s own designers eventually conceded it made the active window harder to pick out, which is a large part of why the next release replaced it with flat, opaque Metro design.