feat(后端架构): 完善后端解耦

ofdgo_geom_backend.go

@@ -0,0 +1,96 @@
+// 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 ofdgo
+
+import "fmt"
+
+// GeometryOperation 指定路径填充区域的布尔运算
+type GeometryOperation uint8
+
+const (
+	GeometryIntersect GeometryOperation = iota
+	GeometryUnion
+	GeometrySubtract
+	GeometryXor
+)
+
+// StrokeOptions 描述毫米单位的描边，Cap和Join使用OFD名称
+// Tolerance为曲线展开误差，0采用后端默认精度，Dashes和DashOffset为绝对长度
+type StrokeOptions struct {
+	Width                             float64
+	Cap, Join                         string
+	MiterLimit, DashOffset, Tolerance float64
+	Dashes                            []float64
+}
+
+// GeometryBackend 操作库自有路径，坐标以页面左上角为原点，不修改任何输入
+// Clip返回nil表示不裁剪，空路径指针表示完全裁去，矩阵映射到页面坐标
+type GeometryBackend interface {
+	Backend
+	Path(object PathObject) (GeometryPath, error)
+	Region(region *Region, matrix Matrix) (GeometryPath, error)
+	Bounds(path GeometryPath) (Box, error)
+	Transform(path GeometryPath, matrix Matrix) (GeometryPath, error)
+	Normalize(path GeometryPath, evenOdd bool) (GeometryPath, error)
+	Combine(left, right GeometryPath, operation GeometryOperation) (GeometryPath, error)
+	Stroke(path GeometryPath, options StrokeOptions) (GeometryPath, error)
+	Clip(renderer *Renderer, clips *Clips, matrix Matrix, parent *GeometryPath) (*GeometryPath, error)
+}
+
+// Geometry 返回当前几何后端，不隐式恢复默认实现
+// 返回: GeometryBackend 几何后端, error 未配置错误
+func (r *Renderer) Geometry() (GeometryBackend, error) {
+	if r.backends.Geometry == nil {
+		return nil, fmt.Errorf("geometry: %w", ErrBackendUnavailable)
+	}
+	return r.backends.Geometry, nil
+}
+
+// Geometry 返回编辑器配置的几何后端
+// 返回: GeometryBackend 几何后端, error 未配置错误
+func (e *Editor) Geometry() (GeometryBackend, error) {
+	if e.backends.Geometry == nil {
+		return nil, fmt.Errorf("geometry: %w", ErrBackendUnavailable)
+	}
+	return e.backends.Geometry, nil
+}
+
+// PathOutline 使用配置的几何后端生成页面坐标中的SVG轮廓
+// 入参: object 路径对象
+// 返回: string SVG路径, error 几何或编码错误
+func (r *Renderer) PathOutline(object PathObject) (string, error) {
+	geometry, err := r.Geometry()
+	if err != nil {
+		return "", err
+	}
+	path, err := geometry.Path(object)
+	if err != nil {
+		return "", err
+	}
+	return path.SVG()
+}
+
+// geometryRectangle 构建页面坐标矩形，保留输入精度
+// 入参: box 矩形范围
+// 返回: GeometryPath 闭合路径
+func geometryRectangle(box Box) GeometryPath {
+	return GeometryPath{
+		{Verb: GeometryMove, End: Point{X: box.X, Y: box.Y}},
+		{Verb: GeometryLine, End: Point{X: box.X + box.W, Y: box.Y}},
+		{Verb: GeometryLine, End: Point{X: box.X + box.W, Y: box.Y + box.H}},
+		{Verb: GeometryLine, End: Point{X: box.X, Y: box.Y + box.H}},
+		{Verb: GeometryClose, End: Point{X: box.X, Y: box.Y}},
+	}
+}