Improve Cesium cruise smoothness

.trellis/spec/blender/asset-generation.md

@@ -121,6 +121,26 @@ catalog.MATERIALS          声明「是什么」    纯 Python，无 bpy
 
 **这类"试过、不行、为什么"的记录要保留。** 删掉它，下一个人会重新引入同一个资产。
 
+## 灌木边缘实例有性能预算
+
+`generate_scene.py` 的 scrub 不是只有贴地面：`natural=scrub` 会先生成
+`Scrub_<way_id>` 地面覆盖，再沿边界实例化 `assets/models/custom/bush/bush.glb`
+（`add_scrub_edge_bushes()`），并在大 scrub 面内部稀疏补树。
+
+这些 bush 是共享 mesh 的多 node 实例。共享 mesh 能压 GLB 体积，但 Cesium 近景 Follow
+仍要处理每个 node / draw。`nantaizi-lake-innovation-valley` 曾经用
+`SCRUB_BUSH_SPACING = 0.82`、`SCRUB_BUSH_LIMIT_PER_PATCH = 180`，结果一个场景有约
+`707` 个 bush nodes；车辆 Follow 到灌木密集区域时明显卡顿。当前预算是：
+
+```python
+SCRUB_BUSH_SPACING = 1.8
+SCRUB_BUSH_LIMIT_PER_PATCH = 60
+```
+
+在 nantaizi 上约 `266` 个 bush nodes，scrub 地面覆盖仍保留。不要只为了“更满”把间距
+调回 1m 以下；那是在把预览流畅度换成近景装饰密度。若确实需要更密的灌木，先换低模
+bush 或做显式 LOD / instancing 方案，再跑 Cesium preview 验证。
+
 ---
 
 ## 确定性：用无理数周期代替 RNG

.trellis/spec/preview/index.md

@@ -162,6 +162,21 @@ let baseStatus = "";
 相机相关的读数必须跟着渲染循环刷新并**做节流**。用 `setInterval` 会在相机快速移动时
 读到过期值，不节流会拖慢帧率。
 
+### 车辆巡航热路径要少分配
+
+车辆巡航是预览层里唯一持续动画的功能。`scripts/lib/cesium-preview.js` 的
+`routeOrientation()` 和 `createChaseFollow()` 每帧都会运行，里面的 `JulianDate`、
+`HeadingPitchRoll`、`Quaternion`、`Matrix4` 等临时对象必须在闭包外复用，不要在
+`CallbackProperty` 或 `viewer.clock.onTick` 回调里 `new`。
+
+预览页面加载的是 30MB+ GLB，动画时 GPU 已经很忙；巡航辅助线也要避免额外透明合成。
+路线 polyline 使用不透明 `Color` 和 `arcType: Cesium.ArcType.NONE`，不要为了视觉效果
+随手改回半透明 geodesic 线。
+
+不要默认降低 `viewer.resolutionScale` 或关闭 antialias/MSAA 来换取巡航流畅度。
+这会让用户误判材质和模型质量。若确实需要性能模式，应做成显式开关，而不是默认牺牲
+预览清晰度。
+
 ### 单资产 vs 多资产的开关
 
 ```js
@@ -207,6 +222,9 @@ python3 -m http.server 8765
 | 用定时器代替 `waitForStableFrames` | 遮罩在材质编译完成前就收起，画面是花的 |
 | 相机读数用 `setInterval` | 快速移动时读到过期值 |
 | 诊断刷新不节流 | 拖慢帧率 |
+| 在车辆每帧回调里创建 `JulianDate` / HPR / 矩阵对象 | 巡航时触发 GC 抖动 |
+| 默认打开半透明路线辅助线 | 增加透明合成成本，主场景可见时车辆更不顺 |
+| 默认降低 `resolutionScale` 或关抗锯齿 | 预览变糊，无法判断材质/模型质量 |
 | 再开一个全局变量 | 已有 `window.osmPreview` |
 | 用 `file://` 打开 | fetch 被拦，卡在加载中 |
 

.trellis/tasks/08-03-smooth-cesium-preview-vehicle-cruise/check.jsonl

@@ -0,0 +1 @@
+{"_example": "Fill with {\"file\": \"<path>\", \"reason\": \"<why>\"}. Put spec/research files only — no code paths. Run `python3 .trellis/scripts/get_context.py --mode packages` to list available specs. Delete this line once real entries are added."}

.trellis/tasks/08-03-smooth-cesium-preview-vehicle-cruise/implement.jsonl

@@ -0,0 +1 @@
+{"_example": "Fill with {\"file\": \"<path>\", \"reason\": \"<why>\"}. Put spec/research files only — no code paths. Run `python3 .trellis/scripts/get_context.py --mode packages` to list available specs. Delete this line once real entries are added."}

.trellis/tasks/08-03-smooth-cesium-preview-vehicle-cruise/prd.md

@@ -0,0 +1,67 @@
+# Smooth Cesium preview vehicle cruise
+
+## Goal
+
+Improve perceived smoothness of vehicle cruise in the Cesium preview for
+`nantaizi-lake-innovation-valley` while the scene model is visible, especially
+when Follow passes through scrub-heavy areas.
+
+The initial preview-layer optimization helped but did not solve the root cause:
+closing `Scene` helps a lot, and the current nantaizi GLB contains about 707
+scrub bush nodes. The root fix is allowed to reduce scrub bush instance density
+while preserving the flat scrub ground cover and existing preview controls.
+
+## Requirements
+
+1. Optimize `scripts/lib/cesium-preview.js` so vehicle animation does less
+   per-frame work during cruise without reducing default visual clarity.
+2. Preserve existing controls and behavior:
+   - Play/Pause still drives `viewer.clock.shouldAnimate`.
+   - Speed slider still maps m/s to clock multiplier.
+   - Vehicle selection still chooses the follow target.
+   - Scene/routes/vehicles/FPS/diagnostics toggles still work.
+   - Follow mode still tracks the selected vehicle.
+3. Keep the preview layer dependency-free and browser-native; no build step,
+   npm dependency, module system, or hard-coded area filenames.
+4. Reduce scrub edge bush instance density in `blender/generate_scene.py` to
+   lower Cesium render load in scrub-heavy Follow views. Preserve deterministic
+   sampling, scrub ground polygons, scrub tree sampling, and scene stats fields.
+5. Regenerate or copy the updated preview JS into
+   `outputs/nantaizi-lake-innovation-valley/cesium-preview.js` only if needed
+   for local manual verification; do not commit generated outputs.
+6. Rebuild `nantaizi-lake-innovation-valley` `blender,cesium,preview` outputs
+   for manual validation. This task intentionally changes generated GLB
+   structure, so full parity-identical output is not expected.
+
+## Acceptance Criteria
+
+- [ ] `scripts/lib/cesium-preview.js` has a small, reviewable optimization that
+      reduces per-frame allocations or render overhead for vehicle cruise.
+- [ ] `blender/generate_scene.py` reduces nantaizi scrub bush node count by at
+      least 50% while keeping scrub polygons present.
+- [ ] Vehicle controls listed in Requirements continue to work by inspection
+      and/or local smoke check.
+- [ ] Blender/Cesium rebuild for `nantaizi-lake-innovation-valley` completes
+      and generated metadata still includes scrub counts.
+- [ ] `node --check scripts/lib/cesium-preview.js` passes.
+- [ ] `python3 -m py_compile blender/generate_scene.py` passes.
+- [ ] If local output preview JS is updated for testing, it remains ignored and
+      is not committed.
+
+## Out Of Scope
+
+- Full scene geometry/material optimization beyond scrub edge bush density.
+- Reducing tree count or changing road/building/water assets.
+- Replacing Cesium or adding profiling libraries.
+- Visual design changes to the preview UI.
+
+## Technical Notes
+
+- User confirmed closing `Scene` improves smoothness, so the scene render load
+  is a real contributor.
+- Current route data is small: `nantaizi-lake-innovation-valley` has 9 route
+  segments and the preview uses at most 5 vehicles.
+- Current nantaizi GLB has 1271 nodes; about 707 are scrub bush nodes. Lowering
+  scrub edge sampling from `0.82m / 180 per patch` to `1.8m / 60 per patch`
+  should reduce nantaizi bush samples to about 266 while leaving scrub ground
+  cover intact.

.trellis/tasks/08-03-smooth-cesium-preview-vehicle-cruise/report.md

@@ -0,0 +1,57 @@
+# Smooth Cesium preview vehicle cruise report
+
+## Root Cause
+
+The first preview-only optimization helped but did not address the main load.
+User testing showed Follow still stuttered in scrub-heavy areas, while disabling
+`Scene` improved smoothness substantially.
+
+Current nantaizi GLB before the scrub-density change:
+
+- GLB nodes: `1271`
+- Scrub bush nodes: `707`
+- Scrub polygons: `5`
+
+The route data is small (`9` route segments, preview uses at most `5` vehicles),
+so route interpolation is not the primary bottleneck.
+
+## Changes
+
+- `scripts/lib/cesium-preview.js`
+  - Route helper polyline is now opaque instead of alpha blended.
+  - Route helper polyline uses `arcType: Cesium.ArcType.NONE`.
+  - Vehicle orientation and chase-follow camera callbacks reuse scratch
+    `JulianDate`, `HeadingPitchRoll`, `Quaternion`, and `Matrix4` objects.
+  - Default Cesium resolution and antialiasing are preserved; no blurry
+    performance mode is enabled by default.
+- `blender/generate_scene.py`
+  - `SCRUB_BUSH_SPACING`: `0.82 -> 1.8`
+  - `SCRUB_BUSH_LIMIT_PER_PATCH`: `180 -> 60`
+  - Scrub ground cover remains unchanged.
+
+## Validation
+
+Commands run:
+
+```bash
+node --check scripts/lib/cesium-preview.js
+python3 -m py_compile blender/generate_scene.py
+python3 -m unittest blender/tests/test_pure.py
+npm run build:area -- --config config/areas/nantaizi-lake-innovation-valley.json --stages blender,cesium,preview
+node scripts/glb-digest.js outputs/nantaizi-lake-innovation-valley/nantaizi-lake-innovation-valley.glb --out /tmp/nantaizi-after-scrub-glb-digest.json
+```
+
+Results after rebuild:
+
+- `SCENE_DONE` reports `scrub_bushes: 266`.
+- GLB nodes: `830`
+- Scrub bush nodes: `266`
+- Scrub polygons in metadata: `5`
+- Route segments in preview route JSON: `9`
+- GLB size: about `31.96 MB`
+
+## Deferred
+
+If Follow still stutters after this density reduction, the next root-level work
+should target the bush asset itself: lower-poly bush mesh, explicit LOD, or a
+proper instancing path supported by Cesium/glTF.

.trellis/tasks/08-03-smooth-cesium-preview-vehicle-cruise/task.json

@@ -0,0 +1,26 @@
+{
+  "id": "smooth-cesium-preview-vehicle-cruise",
+  "name": "smooth-cesium-preview-vehicle-cruise",
+  "title": "Smooth Cesium preview vehicle cruise",
+  "description": "Optimize Cesium preview vehicle cruise smoothness without changing Blender or GLB output.",
+  "status": "in_progress",
+  "dev_type": null,
+  "scope": null,
+  "package": null,
+  "priority": "P2",
+  "creator": "dingkang",
+  "assignee": "dingkang",
+  "createdAt": "2026-08-03",
+  "completedAt": null,
+  "branch": null,
+  "base_branch": "main",
+  "worktree_path": null,
+  "commit": null,
+  "pr_url": null,
+  "subtasks": [],
+  "children": [],
+  "parent": null,
+  "relatedFiles": [],
+  "notes": "",
+  "meta": {}
+}

blender/generate_scene.py

@@ -90,9 +90,9 @@ TUFT_TINT = (0.15, 0.52, 0.09)
 TUFT_TINT_FACTOR = 0.66
 
 SCRUB_BUSH_MODEL = os.path.join(CUSTOM_MODEL_ROOT, "bush", "bush.glb")
-SCRUB_BUSH_SPACING = 0.82
+SCRUB_BUSH_SPACING = 1.8
 SCRUB_BUSH_INSET = 0.38
-SCRUB_BUSH_LIMIT_PER_PATCH = 180
+SCRUB_BUSH_LIMIT_PER_PATCH = 60
 SCRUB_BUSH_HEIGHT = 1.575
 SCRUB_BUSH_SCALE_JITTER = 0.16
 SCRUB_BUSH_LEAF_TINT = (0.075, 0.31, 0.055)

docs/changelog.md

@@ -36,6 +36,14 @@
 - 清理 D3 过期注释债：`tuft_density_wave()` 的说明不再引用已删除的 hedge banding
   对比，`.trellis/spec/guides/artifact-parity-guide.md` 也不再把 D3 列为待修缺陷；
   只改注释 / spec / changelog，未改 Blender 场景生成逻辑。D1 / D2 继续保留为已知约束。
+- 优化 Cesium 预览车辆巡航流畅度：路线辅助线改为不透明非测地线，并复用车辆朝向与
+  跟车相机热路径里的 `JulianDate` / HPR / 矩阵对象，减少巡航时的透明合成和 GC 抖动。
+  默认保留 Cesium 原分辨率和抗锯齿，避免预览变糊；只影响
+  `scripts/lib/cesium-preview.js`，不改变 Blender / GLB / metadata 产物。
+- 从根因降低灌木密集区 Follow 卡顿：`SCRUB_BUSH_SPACING` 从 `0.82m` 调到 `1.8m`，
+  `SCRUB_BUSH_LIMIT_PER_PATCH` 从 `180` 降到 `60`，nantaizi 的 scrub bush nodes
+  `707 -> 266`，GLB 总 nodes `1271 -> 830`；scrub 地面覆盖仍保留 5 个面，默认画质
+  不降级。
 
 ## 2026-07-31（三）远看发黑的真正原因：反照率没被提亮
 

scripts/lib/cesium-preview.js

@@ -365,7 +365,8 @@
       polyline: {
         positions: Cesium.Cartesian3.fromDegreesArrayHeights(flat),
         width: 2,
-        material: routeColor.withAlpha(0.75),
+        material: routeColor,
+        arcType: Cesium.ArcType.NONE,
         clampToGround: false
       }
     });
@@ -434,9 +435,12 @@
     const up = new Cesium.Cartesian3();
     const east = new Cesium.Cartesian3();
     const north = new Cesium.Cartesian3();
+    const aheadTime = new Cesium.JulianDate();
+    const hpr = new Cesium.HeadingPitchRoll(0.0, 0.0, 0.0);
+    const base = new Cesium.Quaternion();
     return new Cesium.CallbackProperty((time, result) => {
       routePosition(route, start, time, speed, current);
-      const aheadTime = Cesium.JulianDate.addSeconds(time, 0.8, new Cesium.JulianDate());
+      Cesium.JulianDate.addSeconds(time, 0.8, aheadTime);
       routePosition(route, start, aheadTime, speed, ahead);
       Cesium.Cartesian3.subtract(ahead, current, direction);
       if (Cesium.Cartesian3.magnitudeSquared(direction) < 0.0001) {
@@ -454,10 +458,13 @@
       Cesium.Cartesian3.normalize(north, north);
       const eastComponent = Cesium.Cartesian3.dot(direction, east);
       const northComponent = Cesium.Cartesian3.dot(direction, north);
-      const heading = Math.atan2(eastComponent, northComponent);
+      hpr.heading = Math.atan2(eastComponent, northComponent);
-      const base = Cesium.Transforms.headingPitchRollQuaternion(
+      Cesium.Transforms.headingPitchRollQuaternion(
         current,
-        new Cesium.HeadingPitchRoll(heading, 0.0, 0.0)
+        hpr,
+        undefined,
+        undefined,
+        base
       );
       return Cesium.Quaternion.multiply(base, correction, result || new Cesium.Quaternion());
     }, false);
@@ -470,6 +477,9 @@
     const scratchEast = new Cesium.Cartesian3();
     const scratchNorth = new Cesium.Cartesian3();
     const scratchUp = new Cesium.Cartesian3();
+    const scratchPreviousTime = new Cesium.JulianDate();
+    const scratchHpr = new Cesium.HeadingPitchRoll(0.0, 0.0, 0.0);
+    const scratchTransform = new Cesium.Matrix4();
     const offset = new Cesium.Cartesian3();
     const state = { enabled: false, distance: 36.0, height: 18.0 };
 
@@ -478,8 +488,8 @@
       const positions = positionsProvider();
       const position = positions.getValue(time, scratchPosition);
       if (!position) return;
-      const previousTime = Cesium.JulianDate.addSeconds(time, -0.8, new Cesium.JulianDate());
+      Cesium.JulianDate.addSeconds(time, -0.8, scratchPreviousTime);
-      const previous = positions.getValue(previousTime, scratchPrevious);
+      const previous = positions.getValue(scratchPreviousTime, scratchPrevious);
       if (previous) {
         Cesium.Cartesian3.subtract(position, previous, scratchDirection);
       } else {
@@ -501,13 +511,16 @@
 
       const eastComponent = Cesium.Cartesian3.dot(scratchDirection, scratchEast);
       const northComponent = Cesium.Cartesian3.dot(scratchDirection, scratchNorth);
-      const heading = Math.atan2(eastComponent, northComponent);
+      scratchHpr.heading = Math.atan2(eastComponent, northComponent);
       Cesium.Cartesian3.fromElements(0.0, -state.distance, state.height, offset);
-      const transform = Cesium.Transforms.headingPitchRollToFixedFrame(
+      Cesium.Transforms.headingPitchRollToFixedFrame(
         position,
-        new Cesium.HeadingPitchRoll(heading, 0.0, 0.0)
+        scratchHpr,
+        undefined,
+        undefined,
+        scratchTransform
       );
-      viewer.camera.lookAtTransform(transform, offset);
+      viewer.camera.lookAtTransform(scratchTransform, offset);
     }
 
     function onWheel(event) {