From b2dfe03d11c4773b90cbcc4261fdcc45a39927c7 Mon Sep 17 00:00:00 2001
From: Neko Ayaka <neko@ayaka.moe>
Date: Thu, 21 May 2026 02:53:02 +0800
Subject: [PATCH] fix(stage-ui-live2d): better blink interval

---
 .../composables/live2d/motion-manager.test.ts | 44 +++++++++++++++++++
 .../src/composables/live2d/motion-manager.ts  |  8 +++-
 2 files changed, 50 insertions(+), 2 deletions(-)

diff --git a/packages/stage-ui-live2d/src/composables/live2d/motion-manager.test.ts b/packages/stage-ui-live2d/src/composables/live2d/motion-manager.test.ts
index ba98bbbed..71577d055 100644
--- a/packages/stage-ui-live2d/src/composables/live2d/motion-manager.test.ts
+++ b/packages/stage-ui-live2d/src/composables/live2d/motion-manager.test.ts
@@ -135,4 +135,48 @@ describe('live2d motion manager plugins', () => {
     expect(context.internalModel.eyeBlink?.updateParameters).not.toHaveBeenCalled()
     expect(context.handled).toBe(true)
   })
+
+  /**
+   * @example
+   * expect(context.model.getParameterValueById('ParamEyeLOpen')).toBeLessThan(1)
+   */
+  it('opens force blink over a randomized 150ms to 300ms duration', () => {
+    const randomSpy = vi.spyOn(Math, 'random')
+      .mockReturnValueOnce(0)
+      .mockReturnValueOnce(0.5)
+
+    const context = createContext({
+      live2dAutoBlinkEnabled: ref(true),
+      live2dForceAutoBlinkEnabled: ref(true),
+      timeDelta: 3,
+    })
+    const plugin = useMotionUpdatePluginAutoEyeBlink(ref(false))
+
+    // ROOT CAUSE:
+    //
+    // Force blink previously reopened at one fixed speed.
+    // That made closed eyes feel either too quick or too slow depending on
+    // the model's eye-open parameter range.
+    //
+    // We fixed this by randomizing each opening phase between 150ms and 300ms.
+    plugin(context)
+    context.timeDelta = 0.075
+    context.handled = false
+    plugin(context)
+    context.timeDelta = 0.15
+    context.handled = false
+    plugin(context)
+
+    expect(context.model.getParameterValueById('ParamEyeLOpen')).toBeCloseTo(4 / 9)
+    expect(context.model.getParameterValueById('ParamEyeROpen')).toBeCloseTo(4 / 9)
+
+    context.timeDelta = 0.075
+    context.handled = false
+    plugin(context)
+
+    expect(context.model.getParameterValueById('ParamEyeLOpen')).toBe(1)
+    expect(context.model.getParameterValueById('ParamEyeROpen')).toBe(1)
+
+    randomSpy.mockRestore()
+  })
 })
diff --git a/packages/stage-ui-live2d/src/composables/live2d/motion-manager.ts b/packages/stage-ui-live2d/src/composables/live2d/motion-manager.ts
index 181573f86..1c9a13010 100644
--- a/packages/stage-ui-live2d/src/composables/live2d/motion-manager.ts
+++ b/packages/stage-ui-live2d/src/composables/live2d/motion-manager.ts
@@ -255,6 +255,7 @@ export function useMotionUpdatePluginAutoEyeBlink(
     startLeft: 1,
     startRight: 1,
     delayMs: 0,
+    openDurationMs: 300,
   }
 
   // Eye values captured at blink start.  Used as the base during
@@ -263,11 +264,13 @@ export function useMotionUpdatePluginAutoEyeBlink(
   let preBlinkLeft = 1.0
   let preBlinkRight = 1.0
   const blinkCloseDuration = 75 // ms
-  const blinkOpenDuration = 75 // ms
+  const minBlinkOpenDuration = 150 // ms
+  const maxBlinkOpenDuration = 300 // ms
   const minDelay = 3000
   const maxDelay = 8000
 
   const clamp01 = (value: number) => Math.min(1, Math.max(0, value))
+  const randomBlinkOpenDuration = () => minBlinkOpenDuration + Math.random() * (maxBlinkOpenDuration - minBlinkOpenDuration)
 
   function resetBlinkState() {
     blinkState.phase = 'idle'
@@ -307,13 +310,14 @@ export function useMotionUpdatePluginAutoEyeBlink(
       if (blinkState.progress >= 1) {
         blinkState.phase = 'opening'
         blinkState.progress = 0
+        blinkState.openDurationMs = randomBlinkOpenDuration()
       }
 
       return { eyeLOpen, eyeROpen }
     }
 
     // Opening: move back to the base with ease-in.
-    blinkState.progress = Math.min(1, blinkState.progress + dt / blinkOpenDuration)
+    blinkState.progress = Math.min(1, blinkState.progress + dt / blinkState.openDurationMs)
     const eased = easeInQuad(blinkState.progress)
     const eyeLOpen = clamp01(blinkState.startLeft * eased)
     const eyeROpen = clamp01(blinkState.startRight * eased)