- Top - The maximum distance above the baseline for the tallest glyph in the font at a given text size.
- Ascent - The recommended distance above the baseline for singled spaced text.
- Descent - The recommended distance below the baseline for singled spaced text.
- Bottom - The maximum distance below the baseline for the lowest glyph in the font at a given text size.
- Leading - The recommended additional space to add between lines of text.
Unicode 字符串
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分段：段落 / script / bidi / font fallback / style run
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shaping：字符 → glyph，并计算 glyph advance / offset
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测量：ascent / descent / leading / baseline / line-height
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换行：word break / CJK break / hyphenation / maxLines / ellipsis
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布局：每一行的 line box、baseline、对齐、justify
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绘制：把 glyph rasterize 到屏幕
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命中测试：点击坐标 ↔ 字符 offset / selection range
Android
- TextView 单行高度 ≈ font metrics + includeFontPadding + lineSpacing
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