ofdgo/ofdgo_renderer_font_canvas.go

// 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"
	"sync"

	"github.com/tdewolff/canvas"
	"github.com/tdewolff/font"
)

// canvasGlyphBoundsLimit 限制单个字体保留的字形与字号边界数量
const canvasGlyphBoundsLimit = 4096

// canvasFontMetrics 保留默认字体度量，写出时不更新原始时间
type canvasFontMetrics struct {
	*font.SFNT
	*fontShaper
	outlines *sfntOutliner
	bounds   *canvasFontBounds
}

// canvasFontBounds 缓存已成功提取的字形边界，不保留轮廓或失败结果
type canvasFontBounds struct {
	mu     sync.Mutex
	values map[canvasGlyphSize]Box
}

// canvasGlyphSize 区分字形编号及精确毫米字号
type canvasGlyphSize struct {
	glyph uint16
	size  float64
}

// ResolveFont 按需加载字体资源，保留内嵌数据及外部字体的名称、样式和集合索引匹配
// 入参: r 渲染器, id 字体标识, exact 是否禁止无关回退
// 返回: ResolvedFont 字体与来源, error 字体不可用错误
func (b CanvasBackend) ResolveFont(r *Renderer, id string, exact bool) (ResolvedFont, error) {
	return r.resolveFontSource(b, id, exact)
}

// OpenFont 解析独立SFNT数据，度量与原有编辑排版保持一致
// 入参: data 字体数据
// 返回: FontMetrics 字体度量, error 解析错误
func (CanvasBackend) OpenFont(data []byte) (FontMetrics, error) {
	sfnt, err := font.ParseSFNT(data, 0)
	if err != nil {
		return nil, err
	}
	metrics := &canvasFontMetrics{SFNT: sfnt, outlines: &sfntOutliner{font: sfnt}, bounds: &canvasFontBounds{}}
	metrics.fontShaper = &fontShaper{metrics: metrics}
	return metrics, nil
}

// Write 返回字体数据，不修改字体元信息
// 返回: []byte 独立SFNT数据
func (f canvasFontMetrics) Write() []byte {
	return fontSFNTData(f.SFNT)
}

// GlyphOutline 返回基线原点、纵轴向下的字形轮廓
// 入参: glyph 字形编号, size 字号，单位为毫米
// 返回: GeometryPath 字形路径, error 字形解析错误
func (f canvasFontMetrics) GlyphOutline(glyph uint16, size float64) (GeometryPath, error) {
	if !rasterPositive(size) || glyph >= f.NumGlyphs() {
		return nil, fmt.Errorf("invalid glyph or size")
	}
	path := &canvas.Path{}
	if err := f.outlines.path(path, glyph, size/float64(f.UnitsPerEm())); err != nil {
		return nil, err
	}
	return *geometryFromCanvasPath(path), nil
}

// GlyphBounds 返回字形轮廓的精确边界，重复编号及字号复用有限缓存
// 入参: glyph 字形编号, size 字号，单位为毫米
// 返回: Box 字形边界, error 字形解析错误
func (f canvasFontMetrics) GlyphBounds(glyph uint16, size float64) (Box, error) {
	key := canvasGlyphSize{glyph: glyph, size: size}
	if f.bounds != nil {
		f.bounds.mu.Lock()
		value, ok := f.bounds.values[key]
		f.bounds.mu.Unlock()
		if ok {
			return value, nil
		}
	}
	outline, err := f.GlyphOutline(glyph, size)
	if err != nil {
		return Box{}, err
	}
	value, err := outline.Bounds()
	if err != nil {
		return Box{}, err
	}
	if f.bounds != nil {
		f.bounds.mu.Lock()
		if f.bounds.values == nil || len(f.bounds.values) >= canvasGlyphBoundsLimit {
			f.bounds.values = make(map[canvasGlyphSize]Box)
		}
		f.bounds.values[key] = value
		f.bounds.mu.Unlock()
	}
	return value, nil
}

// GlyphWarning 返回字形指令栈下溢后保留设计轮廓的提示，原始字体不变
// 入参: glyph 字形编号
// 返回: error 恢复原因，无恢复时为空
func (f canvasFontMetrics) GlyphWarning(glyph uint16) error {
	return f.outlines.glyphWarning(glyph)
}

// GlyphOutlines 批量提取字形轮廓，重复编号只解析一次
// 入参: glyphs 字形编号, size 毫米字号
// 返回: []GeometryPath 同序只读轮廓, error 轮廓错误
func (f canvasFontMetrics) GlyphOutlines(glyphs []uint16, size float64) ([]GeometryPath, error) {
	if !rasterPositive(size) {
		return nil, fmt.Errorf("invalid glyph size")
	}
	result := make([]GeometryPath, len(glyphs))
	paths := make(map[uint16]GeometryPath, len(glyphs))
	for i, glyph := range glyphs {
		path, ok := paths[glyph]
		if !ok {
			var err error
			path, err = f.GlyphOutline(glyph, size)
			if err != nil {
				return nil, err
			}
			paths[glyph] = path
		}
		result[i] = path
	}
	return result, nil
}