blurRampDuration property

How long the backdrop blur takes to ramp from 0 up to settings's blur once the popover starts morphing open.

Why this exists. The per-frame BackdropFilter blur is the dominant raster cost while a popover morphs out of its trigger. Rendering it at full strength from the very first frame pays that cost during the cheapest, still-growing part of the morph — precisely the frames most prone to dropping. Easing the blur in over the morph keeps those early frames cheap and reaches full strength only as the popover settles. Measured on mid-range mobile GPUs this roughly halves the raster time of the open transition (see CHANGELOG.md for 0.21.7 and docs/POPOVER_BLUR_RAMP.md).

Because it is animated continuously (rather than snapped on after a fixed delay) the transition is never visible as an on/off switch — the blur simply blooms in with the glass.

Defaults to Duration(milliseconds: 260) — about the window the liquid morph itself settles in. Set to Duration.zero to disable the ramp and render the blur at full strength from the first frame (the behaviour prior to 0.21.7). The ramp is also skipped automatically when the platform "reduce motion" accessibility setting is active.