diff --git a/include/common.hpp b/include/common.hpp
index 0da9d21..3336fb6 100644
--- a/include/common.hpp
+++ b/include/common.hpp
@@ -9,6 +9,7 @@ enum PtBoundaryRelation { Inside = -1, OnBoundary, Outside = 1 };
 const real PI = std::numbers::pi;
 const real PI2 = 2 * PI;
 const real EPS = std::numeric_limits<real>::epsilon() * 1e2;
+const real EPS_END_PARAM = std::numeric_limits<real>::epsilon() * 1e3;
 const real EPS_NEWTON_ITERATION = std::numeric_limits<real>::epsilon() * 1e6;
 
 const real HALF = 0.5;
diff --git a/include/line.hpp b/include/line.hpp
index c30353d..0c4dd78 100644
--- a/include/line.hpp
+++ b/include/line.hpp
@@ -40,11 +40,15 @@ public:
     int aaa;
     virtual ~ILine() = default;
 
-    virtual Vec3 eval(real param) = 0;
+    virtual Vec3 eval(real t) = 0;
 
-    virtual Vec3 der1(real param) = 0;
+    virtual Vec3 der1(real t) = 0;
 
-    virtual Vec3 der2(real param) = 0;
+    virtual Vec3 der2(real t) = 0;
+
+    virtual Vec3 tangent(real t) = 0;
+
+    virtual Vec3 normal(real t, const Vec3 &tan = -1.) = 0;
 
     virtual ClosestDescOnSeg getClosestParam(const Vec3 &p) = 0;
 
@@ -75,13 +79,42 @@ struct AA {
 
 const real DISC_ARC_ANGLE = std::numbers::pi * 0.125;
 
+namespace detail {
+void initCircularArcInfo(const Vec3 &a, const Vec3 &b, real bugle, const Vec3 &refNormal,
+                         CircularArc<Vec3> &res) {
+    if (isEqual(bugle, 0)) {
+        res.radius = INFINITY;
+        res.theta = 0;
+        res.h = INFINITY;
+        res.inCircleDir = refNormal.cross(b - a).normalize();
+        res.u = res.inCircleDir;
+        res.v = refNormal.cross(res.u);
+        return;
+    }
+
+    Vec3 abHalf = (b - a) * HALF;
+    Vec3 abNorm = abHalf.normalize();
+    real theta = std::atan(fabs(bugle)) * 4;
+    res.inCircleDir = abNorm.cross(refNormal) * (bugle > 0 ? 1 : -1);
+
+    if (fabs(bugle) == 1) {
+        res.h = 0;
+    } else {
+        res.h = abHalf.norm() / std::tan(theta * HALF);
+    }
+    res.center = a + abHalf - res.inCircleDir * res.h;
+    res.theta = theta;
+    res.radius = (res.center - a).norm();
+    res.u = (a - res.center).normalize();
+    res.v = refNormal.cross(res.u);
+}
+} // namespace detail
+
 class Polyline : public ILine {
 public:
-    using Point = Vec3;
-
-    Polyline(Pt3Array points, std::vector<real> bugles, const Vec3 &normal, bool closed = false)
+    Polyline(Pt3Array points, std::vector<real> bugles, const Vec3 &refNormal, bool closed = false)
         : _points(std::move(points)), _bugles(std::move(bugles)), _closed(closed),
-          _normal(normal.normalize()) {
+          _refNormal(refNormal.normalize()) {
         assert(_points.size() >= 2);
         if (closed) {
             assert(_points.size() == _points.size());
@@ -95,7 +128,7 @@ public:
 
     [[nodiscard]] const std::vector<real> &getBugles() const { return _bugles; }
 
-    [[nodiscard]] const Vec3 &getNormal() const { return _normal; }
+    [[nodiscard]] const Vec3 &getRefNormal() const { return _refNormal; }
 
     [[nodiscard]] bool isClosed() const { return _closed; }
 
@@ -106,7 +139,7 @@ public:
 private:
     Pt3Array _points;
     std::vector<real> _bugles;
-    Vec3 _normal;
+    Vec3 _refNormal;
     bool _closed;
 
     std::vector<CircularArc<Vec3>> circularArcs;
@@ -114,51 +147,58 @@ private:
 public:
     void initSegInfo() {
         for (size_t i = 0; i < _bugles.size(); ++i) {
-            const Point &A = _points[i];
-            const Point &B = _points[(i + 1) % _points.size()];
-            Vec3 ABHalf = (B - A) * HALF;
-            Vec3 ABNorm = ABHalf.normalize();
-            real theta = std::atan(_bugles[i]) * 4;
-            circularArcs[i].inCircleDir = _normal.cross(ABNorm) * (fabs(_bugles[i]) > 1 ? -1 : 1);
-            circularArcs[i].h = ABHalf.norm() * std::tan(theta * HALF);
-            circularArcs[i].center = A + ABHalf + circularArcs[i].inCircleDir * circularArcs[i].h;
-            circularArcs[i].theta = theta;
-            circularArcs[i].radius = (circularArcs[i].center - A).norm();
-            circularArcs[i].u = (A - circularArcs[i].center).normalize();
-            circularArcs[i].v = _normal.cross(circularArcs[i].u);
+            detail::initCircularArcInfo(_points[i], _points[(i + 1) % _points.size()], _bugles[i],
+                                        _refNormal, circularArcs[i]);
         }
     }
 
-    Vec3 eval(real param) override {
+    Vec3 eval(real t) override {
         if (circularArcs.empty())
             initSegInfo();
-        int seg = static_cast<int>(param);
-        real tOnSeg = param - seg;
+        int seg = static_cast<int>(t);
+        if (isEqual(_bugles[seg], 0)) {
+            return _points[seg] + (_points[(seg + 1) % _bugles.size()] - _points[seg]) * (t - seg);
+        }
+        real tOnSeg = t - seg;
         const auto &arc = circularArcs[seg];
         real phi = tOnSeg * arc.theta;
         return arc.center + arc.radius * (arc.u * std::cos(phi) + arc.v * std::sin(phi));
     }
 
-    Vec3 der1(real param) override {
+    Vec3 der1(real t) override {
         if (circularArcs.empty())
             initSegInfo();
-        int seg = static_cast<int>(param);
-        real tOnSeg = param - seg;
+        int seg = static_cast<int>(t);
+        if (isEqual(_bugles[seg], 0)) {
+            return _points[(seg + 1) % _bugles.size()] - _points[seg];
+        }
+        real tOnSeg = t - seg;
         const auto &arc = circularArcs[seg];
         real phi = tOnSeg * arc.theta;
         return arc.radius * (arc.u * -std::sin(phi) + arc.v * std::cos(phi));
     }
 
-    Vec3 der2(real param) override {
+    Vec3 der2(real t) override {
         if (circularArcs.empty())
             initSegInfo();
-        int seg = static_cast<int>(param);
-        real tOnSeg = param - seg;
+        int seg = static_cast<int>(t);
+        assert(!isEqual(_bugles[seg], 0));
+        real tOnSeg = t - seg;
         const auto &arc = circularArcs[seg];
         real phi = tOnSeg * arc.theta;
         return -arc.radius * (arc.u * std::cos(phi) + arc.v * std::cos(phi));
     }
 
+    Vec3 tangent(real t) override { return der1(t).normalize(); }
+    // TODO: 试试https://www.jianshu.com/p/9e4877e3965e算出来的结果
+    Vec3 normal(real t, [[maybe_unused]] const Vec3 &tan = -1.) override {
+        if (!isEqual(_bugles[static_cast<int>(t)], 0)) {
+            return -circularArcs[static_cast<int>(t)].inCircleDir;
+        }
+        // 只有对于圆弧这样的特殊曲线是这样
+        return der2(t).normalize();
+    }
+
     // ClosestDescOnSeg getClosestParam(const Vec3 &p) override {
     //     real closestDis = std::numeric_limits<real>::max();
     //     real closestParam;
@@ -221,14 +261,25 @@ public:
     // }
 
     ClosestDescOnSeg getClosestParam(const Vec3 &p) override {
+        if (circularArcs.empty())
+            initSegInfo();
         ClosestDescOnSeg closestDes{};
         for (int i = 0; i < _bugles.size(); ++i) {
             const Vec3 &a = _points[i];
             const Vec3 &b = _points[(i + 1) % _points.size()];
+            if (isEqual(_bugles[i], 0)) {
+                // 点到线段最近距离
+                ClosestDescOnSeg segPtDistRes = segPtDist(p, a, b);
+                if (segPtDistRes.dis < closestDes.dis) {
+                    closestDes = segPtDistRes;
+                    closestDes.t = i + segPtDistRes.t;
+                }
+                continue;
+            }
             const CircularArc<Vec3> &arc = circularArcs[i];
             const Vec3 &o = arc.center;
             // p 到圆弧平面的投影
-            const Vec3 projPt = p - _normal.dot(p - a) * _normal;
+            const Vec3 projPt = p - _refNormal.dot(p - a) * _refNormal;
             // projPt到圆的最近点
             const Vec3 clsPtOnCircle = o + arc.radius * (projPt - o).normalize();
             if ((clsPtOnCircle - a).dot(arc.inCircleDir) > 0) {
@@ -241,7 +292,7 @@ public:
                     real R2 = arc.radius * arc.radius;
                     real cosTheta = (oa).dot(oClsPt) / R2;
                     real theta = std::acos(cosTheta); // [0, pi]
-                    if ((oa.cross(oClsPt)).dot(_normal) < 0) {
+                    if ((oa.cross(oClsPt)).dot(_refNormal) < 0) {
                         theta = 2 * std::numbers::pi - theta;
                     }
                     closestDes.t = i + theta / arc.theta;
@@ -296,7 +347,7 @@ public:
     }
 
     [[nodiscard]] bool isEndParam(real t) const override {
-        return t < EPS || t > static_cast<real>(_bugles.size()) - EPS;
+        return t < EPS_END_PARAM || t > static_cast<real>(_bugles.size()) - EPS_END_PARAM;
     }
 };
 
@@ -330,6 +381,17 @@ public:
         return -_4pi2r_p2 * (_u * std::cos(theta) + _v * std::sin(theta));
     };
 
+    Vec3 tangent(real t) override { return der1(t).normalize(); }
+
+    Vec3 normal(real t, const Vec3 &tan = -1.) override {
+        Vec3 der2Vec = this->der2(t);
+        if (tan == -1.) {
+            Vec3 realTan = tangent(t);
+            return (der2Vec - der2Vec.dot(realTan) * realTan).normalize();
+        }
+        return (der2Vec - der2Vec.dot(tan) * tan).normalize();
+    }
+
     ClosestDescOnSeg getClosestParam(const Vec3 &p) override {
         // discretization and traversal
         real startT = 0;
@@ -418,13 +480,41 @@ class SingleLine : public ILine {
 public:
 };
 
+// 单段圆弧
+// 其实就是
+class ArcLine : public ILine {
+public:
+    ArcLine(const Vec3 &a, const Vec3 &b, real bugle, const Vec3 &refNormal)
+        : _a(a), _b(b), _bugle(bugle), _refNormal(refNormal.normalize()) {}
+
+    bool isEndParam(real t) const override { return t < EPS || t > 1 - EPS; }
+    Vec3 eval(real t) override { return {}; };
+
+    Vec3 der1(real t) override { return {}; };
+
+    Vec3 der2(real t) override { return {}; };
+
+    ClosestDescOnSeg getClosestParam(const Vec3 &p) override { return {}; };
+
+private:
+    Vec3 _a, _b, _refNormal;
+    real _bugle;
+    CircularArc<Vec3> _circularArc;
+
+    void initArcInfo() { detail::initCircularArcInfo(_a, _b, _bugle, _refNormal, _circularArc); }
+};
+
 class PolynomialLine : public ILine {
 public:
-    Vec3 eval(real param) override { return {}; };
+    Vec3 eval(real t) override { return {}; };
+
+    Vec3 der1(real t) override { return {}; };
+
+    Vec3 der2(real t) override { return {}; };
 
-    Vec3 der1(real param) override { return {}; };
+    Vec3 tangent(real t) override { return {}; }
 
-    Vec3 der2(real param) override { return {}; };
+    Vec3 normal(real t, const Vec3 &tan = -1.) override { return {}; }
 
     ClosestDescOnSeg getClosestParam(const Vec3 &p) override { return {}; };
 };
diff --git a/include/solid.hpp b/include/solid.hpp
index e9c3c4f..aa0a1fa 100644
--- a/include/solid.hpp
+++ b/include/solid.hpp
@@ -13,6 +13,11 @@
 class ISolid {
 public:
     virtual ~ISolid() = default;
+    ISolid() = default;
+    ISolid(const ISolid &) = default;
+    ISolid &operator=(const ISolid &) = default;
+    ISolid(ISolid &&) = default;
+    ISolid &operator=(ISolid &&) = default;
 
     virtual real sdf(const Vec3 &p) = 0;
 };
@@ -46,14 +51,14 @@ protected:
     std::vector<std::vector<CircularArc<Vec2>>> _localArcs2d;
     Vec3 _biNormalStartPt;
     IExtrudedSolidBase(std::vector<Polyline> profiles, AxisLineType axis, real rScale)
-        : _profiles(std::move(profiles)), _axis(std::move(axis)), _rScale(rScale) {
+        : ISolid(), _profiles(std::move(profiles)), _axis(std::move(axis)), _rScale(rScale) {
         assert(!_profiles.empty());
         for (const auto &_profile : _profiles) {
             assert(_profile.isClosed());
         }
         // project profile at st point to 2D
-        Vec3 tangent = _axis.der1(0).normalize();
-        Vec3 normal = _axis.der2(0).normalize();
+        Vec3 tangent = _axis.tangent(0);
+        Vec3 normal = _axis.normal(0);
         _biNormalStartPt = tangent.cross(normal);
         Vec3 q = _axis.eval(0);
         size_t profileCount = _profiles.size();
@@ -154,7 +159,7 @@ private:
         for (int i = 0; i < segCount; ++i) {
             const Vec2 &a = loop2D[i];
             const Vec2 &b = loop2D[(i + 1) % segCount];
-            if (arcs2d[i].h <= EPS) {
+            if (arcs2d[i].theta <= EPS) {
                 //straight line segment
                 if (isPointOnSegment(p2D, a, b)) {
                     return OnBoundary;
@@ -236,7 +241,7 @@ private:
             // 需要特殊考虑的情况
             // 从p2D向inCircle方向前进一小步
             Vec2 samplePt = p2D + arcs2d[onLinesegButHasBugle].inCircleDir * EPS;
-            return !ptInPolygon(samplePt) ? Inside : Outside; // 取反
+            return ptInPolygon(samplePt) ? Outside : Inside; // 反过来的
         }
         return ptInPolygon(p2D) ^ inFan ? Inside : Outside;
     }
@@ -314,21 +319,22 @@ class ExtrudedSolidPolyline : public IExtrudedSolidBase<Polyline> {
 public:
     ExtrudedSolidPolyline(std::vector<Polyline> profiles, Polyline axis, real rScale = 1.0)
         : IExtrudedSolidBase(std::move(profiles), std::move(axis), rScale) {
-        assert(_biNormalStartPt.isParallel(_axis.getNormal()));
+        assert(_biNormalStartPt.isParallel(_axis.getRefNormal()));
     }
 
     std::array<Vec3, 3> getTBN(const Vec3 &p, const Vec3 &q, real t) override {
-        if (std::abs(t - std::round(t)) < EPS) {
-            // 端点处
+        if (!_axis.isEndParam(t) && std::abs(t - std::round(t)) < EPS) {
+            // 衔接点处（注意排除断点处）
             // p到圆弧平面的投影
             Vec3 projPt = p - _biNormalStartPt.dot(p - q) * _biNormalStartPt;
             Vec3 normal = (q - projPt).normalize();
-            if (normal.dot(_axis.der2(t)) < 0) {
+            if (normal.dot(_axis.normal(t)) < 0) {
                 normal = -normal;
             }
             return {normal.cross(_biNormalStartPt), normal, _biNormalStartPt};
         }
-        return {_axis.der1(t).normalize(), _axis.der1(t).normalize(), _biNormalStartPt};
+        Vec3 tangent = _axis.tangent(t);
+        return {tangent, _axis.normal(t, tangent), _biNormalStartPt};
     }
 
     // real wnCircularArc(
@@ -371,8 +377,8 @@ public:
 
     std::array<Vec3, 3> getTBN([[maybe_unused]] const Vec3 &a, [[maybe_unused]] const Vec3 &b,
                                real t) override {
-        Vec3 tangent = _axis.der1(t).normalize();
-        Vec3 normal = _axis.der1(t).normalize();
+        Vec3 tangent = _axis.tangent(t);
+        Vec3 normal = _axis.normal(t);
         return {tangent, normal, tangent.cross(normal)};
     }
 };
diff --git a/include/vec.hpp b/include/vec.hpp
index 900b332..83d618d 100644
--- a/include/vec.hpp
+++ b/include/vec.hpp
@@ -120,6 +120,8 @@ public:
     Vec2(real x, real y) : VecBase(x, y) {}
     Vec2(const Vec2 &v) : VecBase(v.x(), v.y()) {}
 
+    Vec2(real v) : VecBase(v) {}
+
     Vec2 &operator=(const Vec2 &v) {
         data = v.data;
         return *this;
@@ -146,6 +148,8 @@ public:
     Vec3(real x, real y, real z) : VecBase(x, y, z) {}
     Vec3(const Vec3 &v) : VecBase(v.x(), v.y(), v.z()) {}
 
+    Vec3(real v) : VecBase(v) {}
+
     Vec3 &operator=(const Vec3 &v) {
         data = v.data;
         return *this;