feat(后端架构): 完善GG后端，修复渐变与选区异常

ofdgo_renderer_geom_gg.go

@@ -0,0 +1,135 @@
+// 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"
+
+	"github.com/gogpu/gg"
+)
+
+// GGGeometryBackend 使用GG处理贝塞尔边界和变换，其他运算由显式配置的几何后端承担
+// GeometryBackend不可为空，椭圆弧保持精确表示，不为接入GG而预先离散化
+type GGGeometryBackend struct{ GeometryBackend }
+
+// Name 返回实际几何提供者组合
+// 返回: string 后端组合标识
+func (b GGGeometryBackend) Name() string { return "gg+" + backendName(b.GeometryBackend) }
+
+// Curves 通过显式配置的曲线适配器展开椭圆弧
+// 入参: path 页面路径
+// 返回: GeometryPath 贝塞尔路径, error 能力或路径错误
+func (b GGGeometryBackend) Curves(path GeometryPath) (GeometryPath, error) {
+	curves, ok := b.GeometryBackend.(GeometryCurves)
+	if !ok {
+		return nil, fmt.Errorf("geometry curves: %w", ErrBackendUnavailable)
+	}
+	return curves.Curves(path)
+}
+
+// Bounds 使用GG计算贝塞尔曲线极值，椭圆弧交给配置的几何后端
+// 入参: path 页面路径
+// 返回: Box 精确范围, error 路径或能力错误
+func (b GGGeometryBackend) Bounds(path GeometryPath) (Box, error) {
+	for _, s := range path {
+		if s.Verb == GeometryArc {
+			if b.GeometryBackend == nil {
+				return Box{}, ErrBackendUnavailable
+			}
+			return b.GeometryBackend.Bounds(path)
+		}
+	}
+	p, err := ggGeometryPath(path)
+	if err != nil {
+		return Box{}, err
+	}
+	if len(path) == 0 {
+		return Box{}, nil
+	}
+	box := p.BoundingBox()
+	return Box{X: box.Min.X, Y: box.Min.Y, W: box.Max.X - box.Min.X, H: box.Max.Y - box.Min.Y}, nil
+}
+
+// Transform 使用GG变换控制点，椭圆弧交给配置的几何后端保持弧线参数
+// 入参: path 页面路径, matrix 页面变换
+// 返回: GeometryPath 新路径, error 路径或变换错误
+func (b GGGeometryBackend) Transform(path GeometryPath, matrix Matrix) (GeometryPath, error) {
+	for _, v := range matrix.Values() {
+		if !finite(v) {
+			return nil, fmt.Errorf("invalid geometry transform")
+		}
+	}
+	for _, s := range path {
+		if s.Verb == GeometryArc {
+			if b.GeometryBackend == nil {
+				return nil, ErrBackendUnavailable
+			}
+			return b.GeometryBackend.Transform(path, matrix)
+		}
+	}
+	p, err := ggGeometryPath(path)
+	if err != nil {
+		return nil, err
+	}
+	return geometryFromGG(p.Transform(gg.Matrix{A: matrix.a, B: matrix.c, C: matrix.e, D: matrix.b, E: matrix.d, F: matrix.f})), nil
+}
+
+// ggGeometryPath 转换贝塞尔路径，不舍入控制点或静默略过指令
+// 入参: path 库路径
+// 返回: *gg.Path GG路径, error 不支持的路径指令
+func ggGeometryPath(path GeometryPath) (*gg.Path, error) {
+	p := gg.NewPath()
+	for _, s := range path {
+		switch s.Verb {
+		case GeometryMove:
+			p.MoveTo(s.End.X, s.End.Y)
+		case GeometryLine:
+			p.LineTo(s.End.X, s.End.Y)
+		case GeometryQuad:
+			p.QuadraticTo(s.Control1.X, s.Control1.Y, s.End.X, s.End.Y)
+		case GeometryCubic:
+			p.CubicTo(s.Control1.X, s.Control1.Y, s.Control2.X, s.Control2.Y, s.End.X, s.End.Y)
+		case GeometryClose:
+			p.Close()
+		default:
+			return nil, fmt.Errorf("unsupported GG geometry command %d", s.Verb)
+		}
+	}
+	return p, nil
+}
+
+// geometryFromGG 返回库自有路径，不保留GG对象
+// 入参: path GG路径
+// 返回: GeometryPath 库路径
+func geometryFromGG(path *gg.Path) GeometryPath {
+	var result GeometryPath
+	path.Iterate(func(verb gg.PathVerb, p []float64) {
+		s := GeometrySegment{}
+		switch verb {
+		case gg.MoveTo:
+			s.Verb, s.End = GeometryMove, Point{p[0], p[1]}
+		case gg.LineTo:
+			s.Verb, s.End = GeometryLine, Point{p[0], p[1]}
+		case gg.QuadTo:
+			s.Verb, s.Control1, s.End = GeometryQuad, Point{p[0], p[1]}, Point{p[2], p[3]}
+		case gg.CubicTo:
+			s.Verb, s.Control1, s.Control2, s.End = GeometryCubic, Point{p[0], p[1]}, Point{p[2], p[3]}, Point{p[4], p[5]}
+		case gg.Close:
+			s.Verb = GeometryClose
+		}
+		result = append(result, s)
+	})
+	return result
+}