feat(后端架构): 优化多后端渲染，修复描边与字形校验

ofdgo_raster_clip.go

@@ -0,0 +1,113 @@
+// 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 (
+	"crypto/sha256"
+	"encoding/binary"
+	"fmt"
+	"image"
+	"image/color"
+	"math"
+)
+
+// rasterClipKey 区分页面尺寸、分辨率和裁剪路径
+// 入参: page 页面, path 页面坐标路径
+// 返回: [32]byte 缓存键
+func rasterClipKey(page *RasterPage, path []RasterSegment) [32]byte {
+	hash := sha256.New()
+	var data [8]byte
+	number := func(v float64) {
+		binary.LittleEndian.PutUint64(data[:], math.Float64bits(v))
+		hash.Write(data[:])
+	}
+	number(page.Width)
+	number(page.Height)
+	number(page.DPI)
+	for _, s := range path {
+		hash.Write([]byte{byte(s.Verb)})
+		for _, p := range []RasterPoint{s.End, s.Control1, s.Control2} {
+			number(p.X)
+			number(p.Y)
+		}
+	}
+	var key [32]byte
+	copy(key[:], hash.Sum(nil))
+	return key
+}
+
+// rasterClipMask 使用所选后端生成区域化透明度蒙版，同页相同裁剪可复用
+// 入参: backend 光栅后端, page 页面, path 页面坐标裁剪, cache 蒙版缓存
+// 返回: *image.Alpha 页面像素坐标蒙版, error 绘制错误
+func rasterClipMask(backend RasterBackend, page *RasterPage, path []RasterSegment, cache *renderCache[[32]byte, *image.Alpha]) (*image.Alpha, error) {
+	key := rasterClipKey(page, path)
+	if mask, ok := cache.get(key); ok {
+		return mask, nil
+	}
+	w, h, err := page.PixelSize()
+	if err != nil {
+		return nil, err
+	}
+	matrix := page.PixelTransform(RasterMatrix{1, 0, 0, 1, 0, 0}, h)
+	minX, minY, maxX, maxY := math.Inf(1), math.Inf(1), math.Inf(-1), math.Inf(-1)
+	include := func(p RasterPoint) {
+		p = matrix.Apply(p)
+		minX = math.Min(minX, p.X)
+		minY = math.Min(minY, p.Y)
+		maxX = math.Max(maxX, p.X)
+		maxY = math.Max(maxY, p.Y)
+	}
+	for _, s := range path {
+		switch s.Verb {
+		case RasterMove, RasterLine:
+			include(s.End)
+		case RasterQuad:
+			include(s.End)
+			include(s.Control1)
+		case RasterCubic:
+			include(s.End)
+			include(s.Control1)
+			include(s.Control2)
+		case RasterClose:
+		default:
+			return nil, fmt.Errorf("invalid clip path command %d", s.Verb)
+		}
+	}
+	if len(path) == 0 || minX > maxX || minY > maxY {
+		return image.NewAlpha(image.Rectangle{}), nil
+	}
+	if !finite(minX) || !finite(minY) || !finite(maxX) || !finite(maxY) {
+		return nil, fmt.Errorf("invalid clip coordinates")
+	}
+	bounds := image.Rect(int(math.Max(0, math.Min(float64(w), math.Floor(minX)-1))), int(math.Max(0, math.Min(float64(h), math.Floor(minY)-1))), int(math.Max(0, math.Min(float64(w), math.Ceil(maxX)+1))), int(math.Max(0, math.Min(float64(h), math.Ceil(maxY)+1))))
+	mask := image.NewAlpha(bounds)
+	if !bounds.Empty() {
+		scale := page.DPI / 25.4
+		local := &RasterPage{Width: float64(bounds.Dx()) / scale, Height: float64(bounds.Dy()) / scale, DPI: page.DPI}
+		local.Commands = []RasterCommand{{Path: path, Paint: RasterPaint{Color: color.RGBA{255, 255, 255, 255}}, Transform: RasterMatrix{1, 0, 0, 1, -float64(bounds.Min.X) / scale, (matrix[5] - float64(bounds.Min.Y)) / scale}}}
+		pixels, err := backend.Render(local)
+		if err != nil {
+			return nil, err
+		}
+		for y := bounds.Min.Y; y < bounds.Max.Y; y++ {
+			for x := bounds.Min.X; x < bounds.Max.X; x++ {
+				_, _, _, alpha := pixels.At(x-bounds.Min.X, y-bounds.Min.Y).RGBA()
+				mask.SetAlpha(x, y, color.Alpha{uint8(alpha >> 8)})
+			}
+		}
+	}
+	cache.put(key, mask, len(mask.Pix)+256)
+	return mask, nil
+}