The window always asked DWM for a full-window blur region and, on
Windows 11, an acrylic backdrop. When the user runs with an opaque
window (low-spec mode or full opacity) that desktop blur is never seen
but DWM still composites it every frame.
- An early read of the saved settings decides whether the window starts
opaque before the backdrop is configured.
- When it does, the full-window blur region is left as SDL's zero-area
default and the backdrop type is set to none instead of acrylic.
Windows-only.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>