After few hours later, I cloud solve this question by myself.
These are difference that my screenshots claim:
・lineFragmentRect
・lineFragmentUsedRect
Please look at the right edge of red borders. These maxX and width are not equal. Assuming from this behavior, I understand that lineFragmentRect is rect for proposing line fragment in glyph layout process, and lineFragmentUsedRect is actual rect that the glyphs are filled, considering word wrap and hyphen factor.
・Code I used for investigation.
func addLineFragmentBorder(of text: String) {
let range = (textView.text as NSString).range(of: text)
let glyphRange = textView.layoutManager.glyphRange(forCharacterRange: range, actualCharacterRange: nil)
// You can try the difference by changing `lineFragmentUsedRect` to `lineFragmentRect`.
let lineRect = textView.layoutManager.lineFragmentUsedRect(forGlyphAt: glyphRange.location, effectiveRange: nil)
let borderLayer = CALayer()
borderLayer.frame = .init(x: lineRect.minX, y: lineRect.minY + textView.textContainerInset.top, width: lineRect.width, height: lineRect.height)
borderLayer.borderColor = UIColor.red.cgColor
borderLayer.borderWidth = 2
borderLayer.backgroundColor = UIColor.clear.cgColor
textView.layer.addSublayer(borderLayer)
}
