在 NSLayoutManager 中获取完全位于给定矩形中的一系列字形

Question

I'm trying to retrieve a glyph range for the given bounds in NSLayoutManager . The built-in methods return the range for glyphs that are wholly or partially lying inside the bounds, and I need to find out which actually fit it.

For example:

let glyphRange = textView.layoutManager!.glyphRange(forBoundingRect: scrollView.contentView.bounds, in: textView.textContainer!)
let charRange = textView.layoutManager!.characterRange(forGlyphRange: glyphRange, actualGlyphRange: nil)

let range = Range(charRange, in: string)

string[range] now produces a substring up to "not listening to explanations useless" .

I've tried creating a substring and removing stuff word by word, until the height of the string fits my needs, but that becomes very slow. I'm writing a method (for both macOS and iOS) which has to take care of hundreds of such calculations in a very short time.

How could I return the range for glyphs wholly inside the bounds?

Answer 1

This can be achieved by enumerating line fragments. They are already laid out, so it comes with not much extra cost.

let desiredHeight = 300
var height = 0.0
textView.layoutManager!.enumerateLineFragments(forGlyphRange: glyphRange) { rect, usedRect, container, range, stop in
    if usedRect.height + usedRect.origin.y <= desiredHeight {
        height += usedRect.height 
    }
}

let newBounds = NSRect(x: 0, y:0, width: width, height: height)
let newGlyphRange = textView.layoutManager!.glyphRange(forBoundingRect: scrollView.contentView.bounds, in: textView.textContainer!)
let newCharRange = textView.layoutManager!.characterRange(forGlyphRange: newGlyphRange, actualGlyphRange: nil)

let newRange = Range(newCharRange, in: string)