binder 几何降级：栈内页用极简几何、封面/环/铆钉降低分段（三角形 357K→24K）

src/scene/binder.js

@@ -85,7 +85,7 @@ function makeSuedeTexture() {
 }
 
 // 圆角矩形轮廓（直线段 + 圆弧段都用 lineTo 细分，正反面/皮边共享同一轮廓）
-function roundedRectShape(w, h, r, edgeSeg = 40, arcSeg = 12) {
+function roundedRectShape(w, h, r, edgeSeg = 16, arcSeg = 10) {
   const hw = w / 2, hh = h / 2;
   const s = new THREE.Shape();
   s.moveTo(-hw + r, hh);
@@ -112,7 +112,7 @@ function roundedRectShape(w, h, r, edgeSeg = 40, arcSeg = 12) {
 // 软皮曲面：ShapeGeometry 三角化（圆角正确、无缺口）+ 书脊处弧度弯曲
 function makeLeatherSurface(w, h, crXY, curve, flip) {
   // 规则网格（含内部顶点，曲面平滑无对角褶痕）+ 角区收缩到圆弧
-  const segX = 128, segY = 96;
+  const segX = 64, segY = 48;
   const hw = w / 2, hh = h / 2;
   const bx = hw - crXY, by = hh - crXY;
   const sigma = 0.5;
@@ -337,7 +337,7 @@ export class Binder {
     plate.receiveShadow = true;
 
     // 铆钉：把薄片钉在牛皮上（覆盖新的铁环范围 ±0.896）
-    const rivetGeo = new THREE.SphereGeometry(0.013, 12, 10);
+    const rivetGeo = new THREE.SphereGeometry(0.013, 8, 6);
     const rivets = [];
     for (const ry of [-0.78, -0.39, 0, 0.39, 0.78]) {
       const rivet = new THREE.Mesh(rivetGeo, mat);
@@ -357,7 +357,7 @@ export class Binder {
       color: 0xd4d7dc, metalness: 0.95, roughness: 0.2,
     });
     // 更平滑的活页环
-    const geo = new THREE.TorusGeometry(RING_R, RING_TUBE, 18, 56);
+    const geo = new THREE.TorusGeometry(RING_R, RING_TUBE, 12, 24);
     this.rings = [];
     for (const u of HOLE_U) {
       const y = (0.5 - u) * PAGE_H;
@@ -370,10 +370,7 @@ export class Binder {
     }
   }
 
-  _buildPages() {
-    const segX = 96, segY = 8;
-
-    ENTRIES.forEach((entry, i) => {
+  _makePageGeometry(segX, segY) {
     const geo = new THREE.PlaneGeometry(PAGE_W, PAGE_H, segX, segY);
     // 页内缘离书脊留出小空隙，左右页不紧贴
     geo.translate(PAGE_W / 2 + PAGE_GAP, 0, 0);
@@ -386,14 +383,25 @@ export class Binder {
       pa.setZ(k, pa.getZ(k) + 0.05 * Math.sin((Math.PI * u) / 2) * (0.8 + 0.2 * yNorm));
     }
     pa.needsUpdate = true;
-      const base = Float32Array.from(geo.attributes.position.array);
+    return geo;
+  }
+
+  _buildPages() {
+    const segX = 96, segY = 8;
+
+    ENTRIES.forEach((entry, i) => {
+      // 高分段几何：翻页/顶层页（弯曲需要足够分段）
+      const hiGeo = this._makePageGeometry(segX, segY);
+      const hiBase = Float32Array.from(hiGeo.attributes.position.array);
+      // 极简几何：栈内页（只露边缘，无需弯曲，2 个三角形）
+      const loGeo = this._makePageGeometry(1, 1);
 
       // 单 mesh + 双面材质：正面登记卡、背面素描（gl_FrontFacing 自动选择）
       // 活页孔用 alphaTest 直接丢弃透明像素（不启用 transparent，避免透明+双面拆两次 draw call）
       const mat = makeTwoSidedMaterial(this.placeholder.front, this.placeholder.back, {
         alphaTest: 0.5,
       });
-      const mesh = new THREE.Mesh(geo, mat);
+      const mesh = new THREE.Mesh(loGeo, mat); // 初始为栈内页，用极简几何
       mesh.castShadow = false; // 由 _restack 依据是否为顶层页控制
 
       const g = new THREE.Group();
@@ -403,8 +411,9 @@ export class Binder {
 
       this.pages.push({
         group: g,
-        geometry: geo,
-        base,
+        hiGeo,
+        loGeo,
+        hiBase,
         material: mat,
         mesh,
         isPlaceholder: true,
@@ -438,7 +447,12 @@ export class Binder {
       const dim = 1 - Math.min(depth * 0.06, 0.22);
       p.material.color.setScalar(dim);
       // 只让顶层（当前右页 + 左侧页）投影，栈内被遮挡页不投影，省阴影 pass
-      p.mesh.castShadow = (j === this.current || j === this.current - 1);
+      const onTop = (j === this.current || j === this.current - 1);
+      p.mesh.castShadow = onTop;
+      // 顶层页用高分段几何（翻页弯曲），栈内页用极简几何（省顶点）
+      if ((p.mesh.geometry === p.hiGeo) !== onTop) {
+        p.mesh.geometry = onTop ? p.hiGeo : p.loGeo;
+      }
     });
     this._updateCurvature();
     this._ensureTextures();
@@ -481,14 +495,15 @@ export class Binder {
     // 翻页时整页柔软弧弯：自由边最高、中段有“腹”、书脊侧贴环；顶边略强于底边；静止时完全平整
     const pages = index === null ? this.pages : [this.pages[index]];
     pages.forEach((p) => {
-      const pos = p.geometry.attributes.position;
+      // 弯曲只作用于高分段几何（顶层/翻页页）；栈内极简几何不弯曲
+      const pos = p.hiGeo.attributes.position;
       const arr = pos.array;
       const theta = Math.abs(p.angle); // 0..π
       const c = Math.sin(theta);       // 0 静止，1 翻页中途
       const A = 0.58 * c;              // 抬升幅度（整页弧）
       for (let i = 0; i < arr.length; i += 3) {
-        const x = p.base[i];
-        const y = p.base[i + 1];
+        const x = p.hiBase[i];
+        const y = p.hiBase[i + 1];
         const s = Math.max(0, x - PAGE_GAP);   // 距页内缘 0..W（防浮点误差产生负值→NaN）
         const u = Math.min(1, s / PAGE_W);     // 0 内缘 .. 1 自由边
         const yNorm = (y + PAGE_H / 2) / PAGE_H; // 0 底边 .. 1 顶边
@@ -496,7 +511,7 @@ export class Binder {
         // 主抬升 + 中段“腹”的次级谐波，曲线更饱满、更柔软
         const belly = 0.85 * Math.sin((Math.PI * u) / 2) + 0.15 * Math.sin(Math.PI * u);
         const z = A * twist * belly;
-        arr[i + 2] = p.base[i + 2] + z;
+        arr[i + 2] = p.hiBase[i + 2] + z;
       }
       pos.needsUpdate = true;
     });
@@ -583,7 +598,8 @@ export class Binder {
 
   dispose() {
     this.pages.forEach((p) => {
-      p.geometry.dispose();
+      p.hiGeo.dispose();
+      p.loGeo.dispose();
       p.material.dispose();
     });
   }