Model

Fixed interface plane at zero tilt · stationary eye on the plane normal (320mm default) · glass rotates around the hinge edge (runtime-resolved, never hardcoded) · per-pixel ray eye→glass→plane, gap-proportional disk blur + darken, black on miss.

Project layout

app/src/main/java/com/example/duofold/
  MainActivity.kt
  ui/FoldEffect.kt       Modifier.foldEffect() — graphicsLayer + RuntimeShader
  ui/FoldParameters.kt   viewDistanceMm, blur/darken tuning
  ui/DemoContentView.kt  realistic demo screen (header + card + list)
  ui/ContentView.kt      root + Recalibrate button + manual tilt slider
  sensors/FoldMotionModel.kt  rotation-vector, zero-pose calibration, hinge
app/src/main/res/raw/duo_fold.agsl   the shader

Build

1. Open this folder in Android Studio (Hedgehog or later).
2. Let it provision Gradle 8.7 + AGP 8.5.2 + SDK 34.
3. Run on a physical device (API 33+) — the emulator has no rotation-vector sensor, so the app boots into manual slider mode there.
4. If Gradle wrapper jars are missing, run gradle wrapper once in this dir.

Use / tune

• Slider: -45°..+45°. Sign flips the hinge (L/R shown in the panel).
• Switch toggles Sensor vs Manual (disabled without a sensor).
• Recalibrate re-zeroes the pose AND resets manual tilt to 0.
• Aesthetics live in FoldParameters + duo_fold.agsl uniforms: viewDistanceMm (320), blurPerMm (0.55), maxBlurRadiusPx (24), darkenPerMm (0.012), maxDarken (0.55).
• Known iteration points: tilt/hinge sign conventions, tap count vs perf (12 taps now), view-distance/blur/darken constants on a real device.

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