Documented foveation's tile artifacts on fine animated textures

- The Quest's GPU applies the fragment density per screen tile and samples textures at a coarser
  level inside reduced-rate tiles, so fine animated detail such as Retro Rewind's swamp goo shows
  square tile edges at the periphery.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

OPENXR.md

@@ -670,7 +670,10 @@ At the Quest's default 0.8 an eye's time goes mostly to geometry and to storing
 resolution. The Wii's shading is cheap, so foveation saves nothing measurable there, although the
 density map verifiably applies (4x4 blocks at the view's edges on High). That is why it defaults to
 `off`. At higher render scales it takes 8 to 22% off the eyes, which is where it earns its keep,
-bought with a softer periphery. It is no fix for a heavy track: on Retro Rewind's SNES Ghost Valley
+bought with a softer periphery. The Quest's GPU applies the density per screen tile, and inside a
+reduced-rate tile it also samples textures one level blurrier per halving. Most surfaces hide it,
+but fine animated detail does not: on Retro Rewind's swamp goo the tiles show as squares where the
+ripples give way to a smoother look. It is no fix for a heavy track: on Retro Rewind's SNES Ghost Valley
 2 at 1.0, GPU-bound at about 40 FPS, no level raised the frame rate, while merging the eye passes
 did (39 to 41.5 FPS).