Issue with NSTextLayoutManager.setRenderingAttributes()

[vgorloff]

If I'm properly understand to solve issue with NSTextLayoutManager.setRenderingAttributes() we literally have to manually setup own "temporary attributes" system. E.g. create a storage to keep instances of NSRange together with needed attributes.

Then in appropriate drawing method we have to draw not a whole fragment (NSTextLayoutFragment), but rather perform line by line drawing (every NSTextLineFragment). But instead of drawing via NSTextLineFragment.draw(at:in:) we have to create a CTLine with appropriate attributes from custom "temporary attributes" storage and finally draw modified attributed string via CTLineDraw().

E.g.

 class CoreTextTextView: CMinimalisticTextView {

   override var isFlipped: Bool {
      return true // Setting to `false` will make `NSTextLineFragment.draw(at:in)` working incorrectly.
   }

   override func drawLayoutFragments(_ fragmentsToDraw: [NSTextLayoutFragment], in context: NSGraphicsContext) {

      func drawLineFragment(_ lineFragment: NSTextLineFragment, at point: CGPoint) {
#if true // If true, the CTLine will be drawn on top of NSTextLineFragment (for sanity/geonetry check).
         lineFragment.draw(at: point, in: context.cgContext)
#endif
         let cgContext = context.cgContext
         cgContext.saveGState()
         let substring = lineFragment.attributedString.attributedSubstring(from: lineFragment.characterRange)
         let newString = NSMutableAttributedString(attributedString: substring)
         newString.addAttribute(.foregroundColor, value: NSColor.yellow, range: NSRange(location: 0, length: newString.length))
         newString.addAttribute(.foregroundColor, value: NSColor.blue, range: NSRange(location: 1, length: 1))
         newString.addAttribute(.underlineStyle, value: NSUnderlineStyle.single.rawValue, range: NSRange(location: 2, length: 4))
         newString.addAttribute(.underlineColor, value: NSColor.magenta, range: NSRange(location: 2, length: 4))
         let ctLine = CTLineCreateWithAttributedString(newString)
         cgContext.textMatrix = CGAffineTransform(scaleX: 1, y: isFlipped ? -1 : 1)
         cgContext.textPosition = point.offsetBy(dx: 0, dy: isFlipped ? lineFragment.glyphOrigin.y: 0)
         CTLineDraw(ctLine, cgContext)
         cgContext.restoreGState()
      }

      for textLayoutFragment in fragmentsToDraw {
         var offset: CGFloat = 0
         for lineFragment in textLayoutFragment.textLineFragments {
            let point = textLayoutFragment.layoutFragmentFrame.origin.offsetY(dy: offset)
            drawLineFragment(lineFragment, at: point)
            offset += lineFragment.typographicBounds.height
         }
      }
   }
}