2026-07-28 17:08:03 +08:00
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# VDE-021: extrude/revolve/sweep/loft 需要 NURBS 曲线输入，缺少 mesh→profile 便捷 API
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- **ID**: VDE-021
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- **Date**: 2026-07-28
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2026-07-29 11:36:47 +08:00
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- **Status**: Fixed
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2026-07-28 17:08:03 +08:00
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- **Severity**: High
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- **Category**: API Gap
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- **Source**: ViewDesign feat/viewdesign-engine branch
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## Issue
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VDE 的扫掠特征 API 全部以 `NurbsCurve` 为输入：
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```cpp
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BrepModel extrude(const NurbsCurve& profile, const Vector3D& dir);
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BrepModel revolve(const NurbsCurve& profile, ...);
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BrepModel sweep(const NurbsCurve& profile, const NurbsCurve& path);
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BrepModel loft(const std::vector<NurbsCurve>& profiles);
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```
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但 ViewDesign 的 `FeatureBuilder` 以 `Shape`（mesh 数据）作为 profile 输入（用户通过二维草图生成的封闭轮廓）：
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```cpp
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Shape extrude(const Shape& profileWire, double dirX, dirY, dirZ, double length);
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```
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从 mesh Shape 中提取 NURBS 曲线轮廓是一个复杂的拟合问题（需要边界检测 + 曲线拟合），VDE 没有提供这样的便捷 API。
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## Impact
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ViewDesign 中 `extrude`/`revolve`/`sweep`/`loft` 保持 OCCT-only，VDE 后端下返回空 Shape。这四个特征是机械 CAD 最常用的建模操作。
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## Suggested Fix
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**方案一（推荐）**：为 VDE 添加从 mesh 提取轮廓的 API
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```cpp
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// 从闭合 mesh 边界提取轮廓曲线
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std::vector<NurbsCurve> extract_profiles_from_mesh(
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const HalfedgeMesh& mesh,
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const Vector3D& projectionAxis = Vector3D(0, 0, 1));
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```
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**方案二**：为建模 API 添加 mesh 输入重载
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```cpp
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BrepModel extrude(const HalfedgeMesh& profileMesh, const Vector3D& dir);
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BrepModel revolve(const HalfedgeMesh& profileMesh, const Vector3D& axis, double angle);
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```
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**方案三**：提供 mesh→NurbsCurve 转换工具
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```cpp
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NurbsCurve mesh_boundary_to_curve(const HalfedgeMesh& mesh);
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```
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