Fixing Energy Loss in IIR-Blurred UI Shadows: Why Renormalisation Matters

IIR blurs make a pretty significant difference in shadow quality compared to integral blurs or even StackBlur approaches. Here's a comparison of the same shadow parameters (drop + inset) for the same mask. The top example is using the fast path (simple integral blur), the bottom one is using IIR (Deriche / Young‑van Vliet). Ignore the aliasing, the source mask (blue) is rendered just for debugging…