feat(后端架构): 完善后端解耦

ofdgo_renderer_canvas.go

@@ -0,0 +1,106 @@
+// 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/tdewolff/canvas"
+	"github.com/tdewolff/canvas/renderers/rasterizer"
+)
+
+// CanvasBackend canvas页面编译与绘制适配器，ColorSpace仅影响光栅输出
+type CanvasBackend struct {
+	ColorSpace canvas.ColorSpace
+}
+
+// Name 返回后端标识
+// 返回: string 后端标识
+func (CanvasBackend) Name() string { return "canvas" }
+
+// Render 绘制已编译页面，不修改输入数据
+// 入参: page 只读页面
+// 返回: image.Image 图像, error 绘制错误
+func (b CanvasBackend) Render(page *RasterPage) (image.Image, error) {
+	w, h, err := page.PixelSize()
+	if err != nil {
+		return nil, err
+	}
+	img := image.NewRGBA(image.Rect(0, 0, w, h))
+	space := b.ColorSpace
+	if space == nil {
+		space = canvas.DefaultColorSpace
+	}
+	r := rasterizer.FromImage(img, canvas.DPMM(page.DPI/25.4), space)
+	for i, cmd := range page.Commands {
+		if cmd.Image != nil {
+			source := cmd.Image
+			if _, linear := space.(canvas.LinearColorSpace); !linear {
+				converted := image.NewRGBA(source.Bounds())
+				for y := source.Bounds().Min.Y; y < source.Bounds().Max.Y; y++ {
+					for x := source.Bounds().Min.X; x < source.Bounds().Max.X; x++ {
+						converted.SetRGBA(x, y, space.ToLinear(color.RGBAModel.Convert(source.At(x, y)).(color.RGBA)))
+					}
+				}
+				source = converted
+			}
+			drawRasterImage(img, source, page.PixelTransform(cmd.Transform, h))
+			continue
+		}
+		p := &canvas.Path{}
+		for _, s := range cmd.Path {
+			switch s.Verb {
+			case RasterMove:
+				p.MoveTo(s.End.X, s.End.Y)
+			case RasterLine:
+				p.LineTo(s.End.X, s.End.Y)
+			case RasterQuad:
+				p.QuadTo(s.Control1.X, s.Control1.Y, s.End.X, s.End.Y)
+			case RasterCubic:
+				p.CubeTo(s.Control1.X, s.Control1.Y, s.Control2.X, s.Control2.Y, s.End.X, s.End.Y)
+			case RasterClose:
+				p.Close()
+			default:
+				return nil, fmt.Errorf("canvas command %d: unsupported path verb %d", i, s.Verb)
+			}
+		}
+		paint := canvas.Paint{Color: cmd.Paint.Color}
+		if g := cmd.Paint.Gradient; g != nil {
+			stops := make(canvas.Grad, len(g.Stops))
+			for j, stop := range g.Stops {
+				stops[j] = canvas.Stop{Offset: stop.Offset, Color: stop.Color}
+			}
+			start, end := canvas.Point{X: g.Start.X, Y: g.Start.Y}, canvas.Point{X: g.End.X, Y: g.End.Y}
+			switch g.Kind {
+			case RasterLinear:
+				paint = canvas.Paint{Gradient: stops.ToLinear(start, end)}
+			case RasterRadial:
+				paint = canvas.Paint{Gradient: stops.ToRadial(start, g.R0, end, g.R1)}
+			default:
+				return nil, fmt.Errorf("canvas command %d: unsupported gradient %d", i, g.Kind)
+			}
+		}
+		style := canvas.Style{Fill: paint, FillRule: canvas.NonZero}
+		if cmd.EvenOdd {
+			style.FillRule = canvas.EvenOdd
+		}
+		m := cmd.Transform
+		r.RenderPath(p, style, canvas.Matrix{{m[0], m[2], m[4]}, {-m[1], -m[3], page.Height - m[5]}})
+	}
+	r.Close()
+	return img, nil
+}