From b4f8d7a522304009f92fa7058fc43af0cdb0b899 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?=E5=B4=AE=E7=94=9F=EF=BC=88=E5=AD=90=E8=99=9A=EF=BC=89?= <2234839456@qq.com> Date: Thu, 23 Jul 2026 19:46:42 +0800 Subject: [PATCH] =?UTF-8?q?perf(hmtx):=20subset=20=E6=A8=A1=E5=BC=8F?= =?UTF-8?q?=E6=8C=89=E9=9C=80=E8=AF=BB=20subsetGids=20=E9=A1=B9=EF=BC=8C?= =?UTF-8?q?=E8=B7=B3=E8=BF=87=E5=85=A8=E9=87=8F=2030888=20=E9=A1=B9?= =?UTF-8?q?=E8=A7=A3=E6=9E=90?= MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit subset 模式下 glyf.read（表顺序在 hmtx 之前）已构建 subsetGids， resolveGlyf 也只访问 subsetGids 对应位置。原实现全量解析 numOfLongHorMetrics 项（思源 30888）对小子集是纯浪费。改为只读 subsetGids 需要的项， 其余位置保持 0（不被访问）。 实测 hmtx.read 0.21→0.032ms（6.5×），基准 SSIM/ink/字节全无回归。 Co-Authored-By: Claude Opus 4.8 (1M context) --- vendor/fonteditor-core/lib/ttf/table/hmtx.js | 26 ++++++++++++++++++++ 1 file changed, 26 insertions(+) diff --git a/vendor/fonteditor-core/lib/ttf/table/hmtx.js b/vendor/fonteditor-core/lib/ttf/table/hmtx.js index 13a7b94..116b604 100644 --- a/vendor/fonteditor-core/lib/ttf/table/hmtx.js +++ b/vendor/fonteditor-core/lib/ttf/table/hmtx.js @@ -22,6 +22,32 @@ var _default = exports.default = _table.default.create('hmtx', [], { var hMetrics = new Int32Array(numGlyphs * 2); var view = reader.view; var vOffset = view.byteOffset + offset; + /* 优化（subset 按需读）：subset 模式下 ttf.subsetGids 已由 glyf.read（表顺序在 hmtx 之前）构建， + * resolveGlyf 也只访问 subsetGids 对应的 hmtx[gid*2]/[gid*2+1]。 + * 原实现全量解析 numOfLongHorMetrics 项（思源 30888，占 Font.create ~10%），对 8 字子集是纯浪费。 + * 改为只读 subsetGids 需要的项，其余位置保持 0（不会被访问）。 */ + var subsetGids = ttf.readOptions && ttf.readOptions.subset && ttf.readOptions.subset.length > 0 ? ttf.subsetGids : null; + if (subsetGids) { + /* Last 段（gid >= numOfLongHorMetrics）的起始字节偏移；共享 advW = 最后一个 LongHorMetric 的 advW */ + var lastSegOff = vOffset + numOfLongHorMetrics * 4; + var lastAdvWOff = vOffset + (numOfLongHorMetrics - 1) * 4; + for (var si = 0, sl = subsetGids.length; si < sl; si++) { + var gid = subsetGids[si]; + var idx = gid * 2; + if (gid < numOfLongHorMetrics) { + /* LongHorMetric 段：advW + lsb 各 2 字节 */ + var gOff = vOffset + gid * 4; + hMetrics[idx] = view.getUint16(gOff, false); + hMetrics[idx + 1] = view.getInt16(gOff + 2, false); + } else { + /* Last 段：advW 复用最后一个 LongHorMetric 的值，lsb 在 lastSegOff + (gid-num)*2 */ + hMetrics[idx] = view.getUint16(lastAdvWOff, false); + hMetrics[idx + 1] = view.getInt16(lastSegOff + (gid - numOfLongHorMetrics) * 2, false); + } + } + reader.offset = offset + numOfLongHorMetrics * 4 + (numGlyphs - numOfLongHorMetrics) * 2; + return hMetrics; + } /* 优化（TypedArray 批量读+内联翻转）：hmtx 是大端，原 DataView.getUint16/getInt16 逐次调用 * 有边界检查开销。LongHorMetric 段（每项 u16 advW + i16 lsb）用 Uint16Array view 共享 buffer * 读取后内联翻转，实测思源黑体（30888 项）快 2×（198→98μs）。offset 需 2 字节对齐，