feat(后端架构): 完善后端解耦

ofdgo_renderer_compile_canvas.go

@@ -0,0 +1,164 @@
+// 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/draw"
+
+	"github.com/tdewolff/canvas"
+)
+
+// CompilePage 使用默认字体和几何解释器生成独立绘制数据
+// 入参: r 渲染器, page 页面内容
+// 返回: *RasterPage 绘制页面, error 编译错误
+func (CanvasBackend) CompilePage(r *Renderer, page *PageContent) (*RasterPage, error) {
+	box, err := r.GetPageBox(page)
+	if err != nil {
+		return nil, err
+	}
+	result := &RasterPage{Width: box.W, Height: box.H, DPI: r.DPI}
+	if _, _, err := result.PixelSize(); err != nil {
+		return nil, err
+	}
+	compiler := &canvasPageCompiler{page: result}
+	if err := r.renderCanvasContext(canvas.NewContext(compiler), page); err != nil {
+		return nil, err
+	}
+	if compiler.err != nil {
+		return nil, compiler.err
+	}
+	return result, nil
+}
+
+// canvasPageCompiler 将已解释的页面绘制转换为自有数据，不保存第三方绘图对象
+type canvasPageCompiler struct {
+	page *RasterPage
+	err  error
+}
+
+// Size 返回物理页面尺寸
+// 返回: float64 宽度, float64 高度
+func (c *canvasPageCompiler) Size() (float64, float64) { return c.page.Width, c.page.Height }
+
+// RenderPath 记录填充并按当前DPI展开描边轮廓
+// 入参: path 路径, style 绘制样式, m 变换矩阵
+func (c *canvasPageCompiler) RenderPath(path *canvas.Path, style canvas.Style, m canvas.Matrix) {
+	if c.err != nil {
+		return
+	}
+	if style.HasFill() {
+		c.fill(path, style.Fill, style.FillRule, m)
+	}
+	if style.HasStroke() {
+		stroke := path
+		if len(style.Dashes) > 0 {
+			offset, dashes := canvas.ScaleDash(style.StrokeWidth, style.DashOffset, style.Dashes)
+			stroke = stroke.Dash(offset, dashes...)
+		}
+		stroke = stroke.Stroke(style.StrokeWidth, style.StrokeCapper, style.StrokeJoiner, canvas.PixelTolerance/(c.page.DPI/25.4))
+		c.fill(stroke, style.Stroke, style.FillRule, m)
+	}
+}
+
+// fill 转换路径和画刷，未知类型返回错误而非丢弃内容
+// 入参: path 路径, paint 画刷, rule 填充规则, m 变换矩阵
+func (c *canvasPageCompiler) fill(path *canvas.Path, paint canvas.Paint, rule canvas.FillRule, m canvas.Matrix) {
+	if c.err != nil || path.Empty() {
+		return
+	}
+	if paint.Pattern != nil {
+		c.err = fmt.Errorf("unsupported raster pattern %T", paint.Pattern)
+		return
+	}
+	cmd := RasterCommand{Paint: RasterPaint{Color: paint.Color}, EvenOdd: rule == canvas.EvenOdd,
+		Transform: RasterMatrix{m[0][0], -m[1][0], m[0][1], -m[1][1], m[0][2], c.page.Height - m[1][2]}}
+	if paint.Gradient != nil {
+		g := &RasterGradient{}
+		var stops canvas.Grad
+		switch source := paint.Gradient.(type) {
+		case *canvas.LinearGradient:
+			g.Kind, g.Start, g.End = RasterLinear, rasterPoint(source.Start), rasterPoint(source.End)
+			stops = source.Grad
+		case *canvas.RadialGradient:
+			g.Kind, g.Start, g.End = RasterRadial, rasterPoint(source.C0), rasterPoint(source.C1)
+			g.R0, g.R1, stops = source.R0, source.R1, source.Grad
+		default:
+			c.err = fmt.Errorf("unsupported raster gradient %T", paint.Gradient)
+			return
+		}
+		g.Stops = make([]RasterStop, len(stops))
+		for i, stop := range stops {
+			g.Stops[i] = RasterStop{Offset: stop.Offset, Color: stop.Color}
+		}
+		cmd.Paint.Gradient = g
+	}
+	path = path.ReplaceArcs()
+	cmd.Path = make([]RasterSegment, 0, path.Len())
+	scanner := path.Scanner()
+	for scanner.Scan() {
+		s := RasterSegment{End: rasterPoint(scanner.End())}
+		switch scanner.Cmd() {
+		case canvas.MoveToCmd:
+			s.Verb = RasterMove
+		case canvas.LineToCmd:
+			s.Verb = RasterLine
+		case canvas.QuadToCmd:
+			s.Verb, s.Control1 = RasterQuad, rasterPoint(scanner.CP1())
+		case canvas.CubeToCmd:
+			s.Verb, s.Control1, s.Control2 = RasterCubic, rasterPoint(scanner.CP1()), rasterPoint(scanner.CP2())
+		case canvas.CloseCmd:
+			s.Verb = RasterClose
+		default:
+			c.err = fmt.Errorf("unsupported raster path command %g", scanner.Cmd())
+			return
+		}
+		cmd.Path = append(cmd.Path, s)
+	}
+	c.page.Commands = append(c.page.Commands, cmd)
+}
+
+// rasterPoint 转换局部坐标点
+// 入参: p 默认引擎坐标点
+// 返回: RasterPoint 独立坐标点
+func rasterPoint(p canvas.Point) RasterPoint { return RasterPoint{X: p.X, Y: p.Y} }
+
+// RenderText 展开已定位字形，使用与目标DPI一致的字形精度
+// 入参: text 文字, m 变换矩阵
+func (c *canvasPageCompiler) RenderText(text *canvas.Text, m canvas.Matrix) {
+	if c.err == nil {
+		text.RenderTo(c, m, canvas.DPMM(c.page.DPI/25.4))
+	}
+}
+
+// RenderImage 记录按像素左上原点定位的图片，旋转或斜切时补充透明采样边距
+// 入参: img 图片, m 变换矩阵
+func (c *canvasPageCompiler) RenderImage(img image.Image, m canvas.Matrix) {
+	if c.err != nil {
+		return
+	}
+	img = imagePixelSource(img)
+	if (m[0][1] != 0 || m[1][0] != 0) && (m[0][0] != 0 || m[1][1] == 0) {
+		bounds := img.Bounds()
+		padded := image.NewRGBA(image.Rect(0, 0, bounds.Dx()+8, bounds.Dy()+8))
+		draw.Draw(padded, image.Rect(4, 4, bounds.Dx()+4, bounds.Dy()+4), img, bounds.Min, draw.Src)
+		img = padded
+		m = m.Translate(-4, -4)
+	}
+	h := float64(img.Bounds().Dy())
+	t := RasterMatrix{m[0][0], -m[1][0], -m[0][1], m[1][1], m[0][2] + m[0][1]*h, c.page.Height - m[1][2] - m[1][1]*h}
+	c.page.Commands = append(c.page.Commands, RasterCommand{Image: img, Transform: t})
+}