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perf(woff2): ttf→woff2 跳过 TTF checksum 计算

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woff2 重新编码，不消费 TTF directory 的 per-table checksum 与
head.checkSumAdjustment（encodeTTFToWOFF2 只读 directory 的 tag/offset/length，
重建自己的 directory）。TTFWriter 加 skipCheckSum 选项，font.write 的 woff2
分支传入，跳过 checkSumArrayBuffer 调用 + directory 回填 + head adjustment。

node --prof 思源 3500 字大字集：checkSumArrayBuffer 5.1%（JS nonlib 第二大）
从热点列表消失。端到端 min -2%（brotli 主导稀释收益），但消除的是语义上
纯无用的计算（被 woff2 丢弃）。head.checkSumAdjustment 保持 0 占位（resolveTTF
已置 0），浏览器渲染不依赖该字段。

ttf 直出（消费 directory checksum）与 woff（ttf2woff 读 directory checksum
写 WOFF 表目录）分支不受影响，仅 woff2 生效。

基准测试全 SSIM 与历史固有值一致（FiraCode 0.9923/初夏纯标点 0.9920/篆体
0.9876 等），woff2 输出字节 IDENTICAL（思源千字文中段 17052/FiraCode 8892/
霞鹜 3840/初夏 6164/6864/得意黑 2532/1628）。

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
This commit is contained in:
崮生（子虚） 2026-07-25 08:02:11 +08:00
parent 2ed666ec58
commit 67d2eb5fa5
2 changed files with 27 additions and 15 deletions
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3
vendor/fonteditor-core/lib/ttf/font.js vendored
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@ -171,7 +171,8 @@ var Font = exports.Font = /*#__PURE__*/function () {
buffer = new _ttfwriter.default(options).write(this.data); buffer = new _ttfwriter.default(options).write(this.data);
buffer = (0, _ttf2woff.default)(buffer, options); buffer = (0, _ttf2woff.default)(buffer, options);
} else if (options.type === 'woff2') { } else if (options.type === 'woff2') {
buffer = new _ttfwriter.default(options).write(this.data); /** 优化316: woff2 重新编码，不消费 TTF directory checksum 与 head.checkSumAdjustment，跳过计算省大字集 ~5% */
buffer = new _ttfwriter.default(Object.assign({}, options, { skipCheckSum: true })).write(this.data);
buffer = (0, _ttftowoff.default)(buffer, options); buffer = (0, _ttftowoff.default)(buffer, options);
} else if (options.type === 'svg') { } else if (options.type === 'svg') {
buffer = (0, _ttf2svg.default)(this.data, options); buffer = (0, _ttf2svg.default)(this.data, options);

39
vendor/fonteditor-core/lib/ttf/ttfwriter.js vendored
View File

@ -28,7 +28,12 @@ var TTFWriter = exports.default = /*#__PURE__*/function () {
writeZeroContoursGlyfData: options.writeZeroContoursGlyfData || false, writeZeroContoursGlyfData: options.writeZeroContoursGlyfData || false,
hinting: options.hinting || false, hinting: options.hinting || false,
kerning: options.kerning || false, kerning: options.kerning || false,
support: options.support support: options.support,
/** 优化316: woff2/woff/eot 输出会重新编码，不消费 TTF directory 的 per-table checksum 与
* head.checkSumAdjustment（encodeTTFToWOFF2 只读 directory 的 tag/offset/length，重建自己的 directory）。
* 跳过 checksum 计算可省大字集下 ~5% 的 checkSumArrayBuffer 开销。head.checkSumAdjustment 保持 0 占位
* （resolveTTF 已置 0），浏览器渲染不依赖该字段。仅 ttf 直出（消费 directory checksum）时不能跳过。 */
skipCheckSum: options.skipCheckSum || false
}; };
} }
@ -136,10 +141,12 @@ var TTFWriter = exports.default = /*#__PURE__*/function () {
* 优化184: 内联 writeEmpty 为 fullView.fill(0)，避免 writer.writeEmpty 的函数调用 + 边界检查开销 */ * 优化184: 内联 writeEmpty 为 fullView.fill(0)，避免 writer.writeEmpty 的函数调用 + 边界检查开销 */
var supportTableList = ttf.support.tables; var supportTableList = ttf.support.tables;
var buf = writer.getBuffer(); var buf = writer.getBuffer();
/** 优化316: skipCheckSum（woff2/woff/eot）时跳过 checksum 计算，head.checkSumAdjustment 保持 0 占位 */
var skipCheckSum = this.options.skipCheckSum;
var wholeCheckSum = 0; var wholeCheckSum = 0;
/** fullView 仍需用于表 padding fill(0)，skipCheckSum 时不必创建 fullDataView */
var fullView = new Uint8Array(buf); var fullView = new Uint8Array(buf);
/** 优化261: 预创建 DataView，复用于所有表的校验和计算，避免每次 checkSumArrayBuffer 创建新 DataView */ var fullDataView = skipCheckSum ? null : new DataView(buf);
var fullDataView = new DataView(buf);
for (var si = 0, sl = supportTableList.length; si < sl; si++) { for (var si = 0, sl = supportTableList.length; si < sl; si++) {
var table = supportTableList[si]; var table = supportTableList[si];
var tableStart = writer.offset; var tableStart = writer.offset;
@ -153,20 +160,24 @@ var TTFWriter = exports.default = /*#__PURE__*/function () {
fullView.fill(0, wView.byteOffset + writer.offset, wView.byteOffset + writer.offset + (4 - pad)); fullView.fill(0, wView.byteOffset + writer.offset, wView.byteOffset + writer.offset + (4 - pad));
writer.offset += 4 - pad; writer.offset += 4 - pad;
} }
table.checkSum = _checkSumArrayBuffer(buf, tableStart, table.size, fullView, fullDataView); if (!skipCheckSum) {
wholeCheckSum = (wholeCheckSum + table.checkSum) >>> 0; table.checkSum = _checkSumArrayBuffer(buf, tableStart, table.size, fullView, fullDataView);
wholeCheckSum = (wholeCheckSum + table.checkSum) >>> 0;
}
} }
/* 优化111: 重新写入校验和，直接 view 写入 */ if (!skipCheckSum) {
var csView = writer.view; /* 优化111: 重新写入校验和，直接 view 写入 */
for (var ci = 0, cl = supportTableList.length; ci < cl; ci++) { var csView = writer.view;
var offset2 = 12 + ci * 16 + 4; for (var ci = 0, cl = supportTableList.length; ci < cl; ci++) {
csView.setUint32(offset2, supportTableList[ci].checkSum, false); var offset2 = 12 + ci * 16 + 4;
} csView.setUint32(offset2, supportTableList[ci].checkSum, false);
}
/* 优化179: 用累加的各表校验和替代全局 checkSum，避免重遍历整个 buffer */ /* 优化179: 用累加的各表校验和替代全局 checkSum，避免重遍历整个 buffer */
var ttfCheckSum = (0xB1B0AFBA - wholeCheckSum) >>> 0; var ttfCheckSum = (0xB1B0AFBA - wholeCheckSum) >>> 0;
csView.setUint32(ttfHeadOffset + 8, ttfCheckSum, false); csView.setUint32(ttfHeadOffset + 8, ttfCheckSum, false);
}
/** 优化260: delete → null 赋值，避免 V8 隐藏类转换 */ /** 优化260: delete → null 赋值，避免 V8 隐藏类转换 */
ttf.writeOptions = null; ttf.writeOptions = null;
ttf.support = null; ttf.support = null;