How to build a progressive blur in Flutter when ShaderMask over BackdropFilter does nothing
Wrapping a BackdropFilter in a ShaderMask removes the blur entirely on both Skia and Impeller. Here is why, plus two working progressive blurs: stepped BackdropFilter bands that work everywhere, and a variable-radius Gaussian through ImageFilter.shader on Impeller, both measured pixel by pixel in Flutter 3.44.8.