feat(文件拆分): 拆分几何三维基础能力

internal/base/threed/u3d_pointset.go

@@ -0,0 +1,71 @@
+// Copyright 2025-2026 肖其顿 (XIAO QI DUN)
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package threed
+
+import (
+	"fmt"
+	"math"
+)
+
+// pointNormalPrediction 按ECMA-363第9.6.2.2.4.4节计算点集球面法线预测
+// 入参: mesh 属性数组, points 分裂位置的点
+// 返回: u3dVector 预测方向, error 不支持的多方向预测或取消错误
+func (d *u3dDecoder) pointNormalPrediction(mesh *U3DMesh, points []U3DPoint) (u3dVector, error) {
+	var directions [2]u3dVector
+	var counts [2]int
+	var previous [3]float32
+	var direction u3dVector
+	for i, point := range points {
+		if i%256 == 0 {
+			if err := d.ctx.Err(); err != nil {
+				return u3dVector{}, err
+			}
+		}
+		normal := mesh.Normals[point.Corners[0].Normal]
+		if i == 0 || normal != previous {
+			direction = (u3dVector{float64(normal[0]), float64(normal[1]), float64(normal[2])}).unit()
+			previous = normal
+		}
+		if counts[0] == 0 || direction == directions[0] {
+			directions[0] = direction
+			counts[0]++
+		} else if counts[1] == 0 || direction == directions[1] {
+			directions[1] = direction
+			counts[1]++
+		} else {
+			return u3dVector{}, fmt.Errorf("unsupported U3D point normal prediction with multiple directions")
+		}
+	}
+	if counts[1] == 0 {
+		return directions[0], nil
+	}
+	a, b := directions[0], directions[1]
+	if a == (u3dVector{}) || b == (u3dVector{}) {
+		return u3dVector{}, fmt.Errorf("unsupported U3D point normal prediction with zero direction")
+	}
+	dot := max(-1, min(1, a.dot(b)))
+	tangent := b.sub(u3dVector{a[0] * dot, a[1] * dot, a[2] * dot})
+	length := math.Sqrt(tangent.dot(tangent))
+	if length == 0 {
+		return u3dVector{}, fmt.Errorf("unsupported U3D antipodal point normal prediction")
+	}
+	angle := math.Atan2(length, dot) * (float64(counts[1]) / float64(len(points)))
+	sine, cosine := math.Sincos(angle)
+	var result u3dVector
+	for i := range result {
+		result[i] = a[i]*cosine + tangent[i]/length*sine
+	}
+	return result.unit(), nil
+}