feat(资源管理): 修复字体预览与资源定位

ofdgo_render_preview.go

@@ -16,6 +16,7 @@ package ofdgo
 
 import (
 	"bytes"
+	"context"
 	"crypto/sha256"
 	"fmt"
 	"io"
@@ -55,3 +56,70 @@ func (r *Renderer) RenderPreview(page *PageContent, writer io.Writer, options Pr
 	}
 	return SVGResources{Images: []SVGImage{{Name: name, MIME: "image/png", Data: pixels.Bytes()}}}, nil
 }
+
+// RenderFontPreview 将指定字体的前32个可见字形绘制为独立SVG，不依赖字符映射或浏览器字体
+// 排除缺字字形，外部字体须精确匹配，不修改原始资源或使用无关回退字体
+// 入参: ctx 取消上下文, id 字体资源标识, writer 输出流
+// 返回: error 字体、轮廓、取消或写入错误
+func (r *Renderer) RenderFontPreview(ctx context.Context, id string, writer io.Writer) error {
+	if err := ctx.Err(); err != nil {
+		return err
+	}
+	view := *r
+	view.pageContext = ctx
+	resolved, err := view.ResolveFont(id, true)
+	if err != nil {
+		return err
+	}
+	font := &PreparedFont{ResolvedFont: resolved}
+	if definition := view.Reader.fontDefinition(id); definition != nil && definition.FontFile != "" {
+		font, err = view.PrepareFont(id)
+		if err != nil {
+			return err
+		}
+	}
+	metrics, err := view.preparedMetrics(font)
+	if err != nil {
+		return err
+	}
+	outlines, ok := metrics.(FontOutlines)
+	if !ok {
+		return fmt.Errorf("font outlines: %w", ErrBackendUnavailable)
+	}
+	var paths bytes.Buffer
+	count := 0
+	for glyph := uint16(1); glyph < metrics.NumGlyphs() && count < 32; glyph++ {
+		if err := ctx.Err(); err != nil {
+			return err
+		}
+		outline, err := outlines.GlyphOutline(glyph, 24)
+		if err != nil {
+			return err
+		}
+		box, err := outline.Bounds()
+		if err != nil {
+			return err
+		}
+		if box.W <= 0 || box.H <= 0 {
+			continue
+		}
+		path, err := outline.SVG()
+		if err != nil {
+			return err
+		}
+		scale := min(1.0, 28/box.W, 32/box.H)
+		x := float64(count%8)*36 + (36-box.W*scale)/2 - box.X*scale
+		y := float64(count/8)*40 + (40-box.H*scale)/2 - box.Y*scale
+		fmt.Fprintf(&paths, `<path transform="translate(%g %g) scale(%g)" d="%s"/>`, x, y, scale, path)
+		count++
+	}
+	if err := ctx.Err(); err != nil {
+		return err
+	}
+	if count == 0 {
+		return fmt.Errorf("font has no visible glyphs")
+	}
+	width, height := min(count, 8)*36, (count+7)/8*40
+	_, err = fmt.Fprintf(writer, `<svg xmlns="http://www.w3.org/2000/svg" width="%d" height="%d" viewBox="0 0 %d %d">%s</svg>`, width, height, width, height, paths.Bytes())
+	return err
+}