fix: mitigate VRM chin mesh artifacts by clamping mouth weight, adjusting jaw rotation, forcing double-sided rendering, and refining viseme defaults

ui/vrm.py

@@ -252,9 +252,11 @@ def avatar_html(vrm_urls: str | list[str]) -> str:
       if (persistent) persistentEmotion = name;
     }}
 
+    const MAX_MOUTH_WEIGHT = 0.7; // Cap mouth open to prevent chin mesh stretching artifacts
+
     function setMouth(weight, viseme = 'ih') {{
       if (!vrm) return;
-      const clamped = Math.max(0, Math.min(1, Number(weight) || 0));
+      const clamped = Math.max(0, Math.min(MAX_MOUTH_WEIGHT, Number(weight) || 0));
       let preset  = VISEME_MAP[viseme] ?? viseme ?? 'ih';
       if (preset === 'aa') preset = 'ih'; // Disable 'aa' completely due to chin artifact
       let usedExpression = false;
@@ -265,16 +267,10 @@ def avatar_html(vrm_urls: str | list[str]) -> str:
             usedExpression = true;
           }}
         }}
-        try {{
-          const em = vrm.expressionManager;
-          if (em._expressions) {{
-            em._expressions.forEach(expr => expr.applyWeight({{ multiplier: 1 }}));
-          }}
-        }} catch (_) {{}}
       }}
       if (!usedExpression) {{
         const jaw = vrm.humanoid?.getNormalizedBoneNode?.('jaw') || vrm.humanoid?.getRawBoneNode?.('jaw');
-        if (jaw) jaw.rotation.x = clamped * 0.5;
+        if (jaw) jaw.rotation.x = clamped * 0.35;
       }}
     }}
 
@@ -720,7 +716,18 @@ def avatar_html(vrm_urls: str | list[str]) -> str:
         vrm = gltf.userData.vrm;
         window._aikoVrm = vrm;
         VRMUtils.removeUnnecessaryVertices(vrm.scene);
-        vrm.scene.traverse(o => {{ if (o.frustumCulled) o.frustumCulled = false; }});
+        vrm.scene.traverse(o => {{
+          if (o.frustumCulled) o.frustumCulled = false;
+          // Fix white chin artifacts: force double-sided rendering so
+          // back-faces of stretched mouth/chin geometry render correctly
+          // instead of showing as bright white patches.
+          if (o.isMesh && o.material) {{
+            const mats = Array.isArray(o.material) ? o.material : [o.material];
+            for (const mat of mats) {{
+              mat.side = THREE.DoubleSide;
+            }}
+          }}
+        }});
         vrm.scene.rotation.y = 0;
         scene.add(vrm.scene);
 
@@ -758,12 +765,12 @@ def avatar_html(vrm_urls: str | list[str]) -> str:
       const audioMouth = speaking ? getAudioMouth()       : null;
 
       if (audioMouth !== null) {{
-        setMouth(audioMouth, textMouth?.viseme ?? 'aa');
+        setMouth(audioMouth, textMouth?.viseme ?? 'ih');
       }} else if (textMouth) {{
         setMouth(textMouth.weight, textMouth.viseme);
       }} else if (speaking) {{
-        mouth = 0.12 + Math.abs(Math.sin(now / 110)) * 0.65;
-        setMouth(mouth, 'aa');
+        mouth = 0.10 + Math.abs(Math.sin(now / 110)) * 0.50;
+        setMouth(mouth, 'ih');
       }} else {{
         smoothedAudioMouth = 0;
         clearMouth();