feat(后端架构): 完善后端解耦

ofdgo_renderer_gg.go

@@ -0,0 +1,101 @@
+// 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"
+	"image"
+	"image/color"
+
+	"github.com/gogpu/gg"
+)
+
+// GGBackend 不注册全局GPU设备或回退到其他绘图库的CPU后端
+type GGBackend struct{}
+
+// Name 返回后端标识
+// 返回: string 后端标识
+func (GGBackend) Name() string { return "gg" }
+
+// Render 绘制已编译页面，使用自有双圆渐变语义保持原有定位
+// 入参: page 只读页面
+// 返回: image.Image 图像, error 绘制错误
+func (GGBackend) Render(page *RasterPage) (image.Image, error) {
+	w, h, err := page.PixelSize()
+	if err != nil {
+		return nil, err
+	}
+	pixmap := gg.NewPixmap(w, h)
+	img := pixmap.ImageView()
+	raster := gg.NewSoftwareRenderer(w, h)
+	for i, cmd := range page.Commands {
+		m := page.PixelTransform(cmd.Transform, h)
+		if cmd.Image != nil {
+			drawRasterImage(img, cmd.Image, m)
+			continue
+		}
+		path := gg.NewPath()
+		for _, s := range cmd.Path {
+			end, c1, c2 := m.Apply(s.End), m.Apply(s.Control1), m.Apply(s.Control2)
+			switch s.Verb {
+			case RasterMove:
+				path.MoveTo(end.X, end.Y)
+			case RasterLine:
+				path.LineTo(end.X, end.Y)
+			case RasterQuad:
+				path.QuadraticTo(c1.X, c1.Y, end.X, end.Y)
+			case RasterCubic:
+				path.CubicTo(c1.X, c1.Y, c2.X, c2.Y, end.X, end.Y)
+			case RasterClose:
+				path.Close()
+			default:
+				return nil, fmt.Errorf("gg command %d: unsupported path verb %d", i, s.Verb)
+			}
+		}
+		paint := gg.NewPaint()
+		paint.SetFillBrush(gg.SolidBrush{Color: ggRGBA(cmd.Paint.Color)})
+		if g := cmd.Paint.Gradient; g != nil {
+			if g.Kind != RasterLinear && g.Kind != RasterRadial {
+				return nil, fmt.Errorf("gg command %d: unsupported gradient %d", i, g.Kind)
+			}
+			inverse, err := m.Inverse()
+			if err != nil {
+				return nil, fmt.Errorf("gg command %d: %w", i, err)
+			}
+			paint.SetFillBrush(gg.NewCustomBrush(func(x, y float64) gg.RGBA {
+				p := inverse.Apply(RasterPoint{X: x, Y: y})
+				return ggRGBA(g.At(p.X, p.Y))
+			}))
+		}
+		if cmd.EvenOdd {
+			paint.FillRule = gg.FillRuleEvenOdd
+		}
+		if err := raster.Fill(pixmap, path, paint); err != nil {
+			return nil, fmt.Errorf("gg command %d: %w", i, err)
+		}
+	}
+	return img, nil
+}
+
+// ggRGBA 将标准库预乘颜色转换为gg的非预乘颜色
+// 入参: c 预乘颜色
+// 返回: gg.RGBA 非预乘颜色
+func ggRGBA(c color.RGBA) gg.RGBA {
+	if c.A == 0 {
+		return gg.Transparent
+	}
+	a := float64(c.A)
+	return gg.RGBA{R: float64(c.R) / a, G: float64(c.G) / a, B: float64(c.B) / a, A: a / 255}
+}