feat(后端架构): 完善GG后端，修复渐变与选区异常

ofdgo_renderer_font_gg.go

@@ -0,0 +1,117 @@
+// 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 (
+	"bytes"
+	"fmt"
+	"math"
+
+	ggtext "github.com/gogpu/gg/text"
+)
+
+// ResolveFont 使用公共字体来源匹配，不创建Canvas字体
+// 入参: r 渲染器, id 字体ID, exact 是否禁止无关回退
+// 返回: ResolvedFont 字体及来源, error 解析错误
+func (b GGBackend) ResolveFont(r *Renderer, id string, exact bool) (ResolvedFont, error) {
+	return r.resolveFontSource(b, id, exact)
+}
+
+// OpenFont 通过GG解析独立字体，保留原始SFNT编码
+// 入参: data 字体数据
+// 返回: FontMetrics 字体度量, error 解析错误
+func (GGBackend) OpenFont(data []byte) (FontMetrics, error) {
+	data = bytes.Clone(data)
+	source, err := ggtext.NewFontSource(data)
+	if err != nil {
+		return nil, err
+	}
+	return &ggFontMetrics{font: source.Parsed(), data: data}, nil
+}
+
+// ggFontMetrics 适配GG设计单位度量与字形轮廓
+type ggFontMetrics struct {
+	font ggtext.ParsedFont
+	data []byte
+}
+
+// UnitsPerEm 返回字体设计单位
+// 返回: uint16 每字单位数
+func (f *ggFontMetrics) UnitsPerEm() uint16 { return uint16(f.font.UnitsPerEm()) }
+
+// NumGlyphs 返回字形数量
+// 返回: uint16 字形数量
+func (f *ggFontMetrics) NumGlyphs() uint16 { return uint16(f.font.NumGlyphs()) }
+
+// GlyphIndex 返回字符对应的字形编号
+// 入参: character 字符
+// 返回: uint16 字形编号
+func (f *ggFontMetrics) GlyphIndex(character rune) uint16 { return f.font.GlyphIndex(character) }
+
+// GlyphAdvance 返回字形设计单位推进宽度
+// 入参: glyph 字形编号
+// 返回: uint16 推进宽度
+func (f *ggFontMetrics) GlyphAdvance(glyph uint16) uint16 {
+	return uint16(math.Round(f.font.GlyphAdvance(glyph, float64(f.font.UnitsPerEm()))))
+}
+
+// VerticalMetrics 返回非负的上升、下降与行间隙
+// 返回: uint16 上升高度, uint16 下降高度, uint16 行间隙
+func (f *ggFontMetrics) VerticalMetrics() (uint16, uint16, uint16) {
+	m := f.font.Metrics(float64(f.font.UnitsPerEm()))
+	return uint16(math.Round(math.Max(0, m.Ascent))), uint16(math.Round(math.Max(0, -m.Descent))), uint16(math.Round(math.Max(0, m.LineGap)))
+}
+
+// Write 返回独立字体数据，不更新字体元信息
+// 返回: []byte SFNT数据
+func (f *ggFontMetrics) Write() []byte { return bytes.Clone(f.data) }
+
+// GlyphOutline 返回基线原点、纵轴向下的字形路径
+// 入参: glyph 字形编号, size 字号，单位为毫米
+// 返回: GeometryPath 字形路径, error 轮廓解析错误
+func (f *ggFontMetrics) GlyphOutline(glyph uint16, size float64) (GeometryPath, error) {
+	if !rasterPositive(size) || int(glyph) >= f.font.NumGlyphs() {
+		return nil, fmt.Errorf("invalid glyph or size")
+	}
+	outline, err := ggtext.NewOutlineExtractor().ExtractOutline(f.font, ggtext.GlyphID(glyph), size)
+	if err != nil || outline == nil {
+		return nil, err
+	}
+	result := make(GeometryPath, 0, len(outline.Segments)+1)
+	point := func(p ggtext.OutlinePoint) Point { return Point{X: float64(p.X), Y: float64(p.Y)} }
+	for _, s := range outline.Segments {
+		segment := GeometrySegment{End: point(s.Points[0])}
+		switch s.Op {
+		case ggtext.OutlineOpMoveTo:
+			if len(result) > 0 {
+				result = append(result, GeometrySegment{Verb: GeometryClose})
+			}
+			segment.Verb = GeometryMove
+		case ggtext.OutlineOpLineTo:
+			segment.Verb = GeometryLine
+		case ggtext.OutlineOpQuadTo:
+			segment.Verb, segment.Control1, segment.End = GeometryQuad, point(s.Points[0]), point(s.Points[1])
+		case ggtext.OutlineOpCubicTo:
+			segment.Verb, segment.Control1, segment.Control2, segment.End = GeometryCubic, point(s.Points[0]), point(s.Points[1]), point(s.Points[2])
+		default:
+			return nil, fmt.Errorf("unsupported GG outline command %d", s.Op)
+		}
+		result = append(result, segment)
+	}
+	if len(result) > 0 {
+		result = append(result, GeometrySegment{Verb: GeometryClose})
+	}
+	return result, nil
+}