From 487e567d4c7161e8a152d5781be52a949bf4518e Mon Sep 17 00:00:00 2001
From: InfinityPacer <160988576+InfinityPacer@users.noreply.github.com>
Date: Tue, 4 Aug 2026 19:48:44 +0800
Subject: [PATCH] fix(glass): define signed coverage square (#642)

---
 .../__tests__/glassFluidDynamics.spec.ts      | 22 +++++++++++--------
 src/rendering/glass/glassFluidDynamics.ts     |  3 ++-
 2 files changed, 15 insertions(+), 10 deletions(-)

diff --git a/src/rendering/glass/__tests__/glassFluidDynamics.spec.ts b/src/rendering/glass/__tests__/glassFluidDynamics.spec.ts
index 5d9e4d59..b933f399 100644
--- a/src/rendering/glass/__tests__/glassFluidDynamics.spec.ts
+++ b/src/rendering/glass/__tests__/glassFluidDynamics.spec.ts
@@ -195,17 +195,21 @@ describe('glass fluid dynamics', () => {
   })
 
   it('narrows directional material coverage without replacing fluid refraction energy', () => {
-    expect(GLASS_FLUID_FRAGMENT_SURFACE_SHAPE).toContain(
-      'smoothstep(0.001, 0.012, length(uPointerVelocity))',
-    )
+    expect(GLASS_FLUID_FRAGMENT_SURFACE_SHAPE).toContain('smoothstep(0.001, 0.012, length(uPointerVelocity))')
     expect(GLASS_FLUID_FRAGMENT_SURFACE_SHAPE).toContain('directionalCoverageShape')
     expect(GLASS_FLUID_FRAGMENT_SURFACE_SHAPE).toContain('pointerCoverageEnergy')
-    expect(GLASS_FLUID_FRAGMENT_SURFACE_SHAPE).toContain(
-      'pow(clamp(pointerCoverageShape * uMotion, 0.0, 1.0), 1.15)',
-    )
-    expect(GLASS_FLUID_FRAGMENT_SURFACE_REFRACTION).toContain(
-      'pointerDelta * pointerEnergy * pointerStrength',
-    )
+    expect(GLASS_FLUID_FRAGMENT_SURFACE_SHAPE).toContain('pow(clamp(pointerCoverageShape * uMotion, 0.0, 1.0), 1.15)')
+    expect(GLASS_FLUID_FRAGMENT_SURFACE_REFRACTION).toContain('pointerDelta * pointerEnergy * pointerStrength')
     expect(GLASS_FLUID_FRAGMENT_SURFACE_REFRACTION).not.toContain('pointerCoverageEnergy')
   })
+
+  it('squares the signed coverage offset without GLSL pow', () => {
+    expect(GLASS_FLUID_FRAGMENT_SURFACE_SHAPE).toContain(
+      'float directionalCoverageAlong = pointerAlong + coverageWakeTravel * 0.45;',
+    )
+    expect(GLASS_FLUID_FRAGMENT_SURFACE_SHAPE).toContain(
+      'directionalCoverageAlong * directionalCoverageAlong * pointerSpread * 0.55',
+    )
+    expect(GLASS_FLUID_FRAGMENT_SURFACE_SHAPE).not.toContain('pow(pointerAlong + coverageWakeTravel * 0.45, 2.0)')
+  })
 })
diff --git a/src/rendering/glass/glassFluidDynamics.ts b/src/rendering/glass/glassFluidDynamics.ts
index 67bd4df3..fb837c22 100644
--- a/src/rendering/glass/glassFluidDynamics.ts
+++ b/src/rendering/glass/glassFluidDynamics.ts
@@ -223,8 +223,9 @@ export const GLASS_FLUID_FRAGMENT_SURFACE_SHAPE = `    vec2 pointerDelta = uPoin
     );
     float coverageWakeTravel =
       0.08 * coverageDirectionality * mix(0.86, 1.18, uMotionExpansion);
+    float directionalCoverageAlong = pointerAlong + coverageWakeTravel * 0.45;
     float directionalCoverageShape = exp(-(
-      pow(pointerAlong + coverageWakeTravel * 0.45, 2.0) * pointerSpread * 0.55 +
+      directionalCoverageAlong * directionalCoverageAlong * pointerSpread * 0.55 +
       pointerAcross * pointerAcross * pointerSpread * 2.8
     ));
     float pointerCoverageShape = mix(