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swiftnsattributedstringcore-textcgrect

Why does drawing using CoreText require increasing the size of the CGRect?

I'm trying to draw text using CoreText. I have the following code:

guard let context = UIGraphicsGetCurrentContext() else { return }

let attrString = NSAttributedString(string: "Str")
let path = CGMutablePath()

// Commented code does work, why?
// path.addRect(CGRect(x: 0, y: 50, width: attrString.size().width + 1, height: attrString.size().height + 1))
path.addRect(CGRect(x: 0, y: 50, width: attrString.size().width, height: attrString.size().height))

let framesetter = CTFramesetterCreateWithAttributedString(attrString as CFAttributedString)
let frame = CTFramesetterCreateFrame(framesetter, CFRangeMake(0, attrString.length), path, nil)

CTFrameDraw(frame, context)

Why does increasing the size of CGRect help, while the actual size of NSAttributedString doesn't?

Any help is appreciated.

Solution

  • When working with an attributed string and getting its size, you need to at least specify a font. The size of "Str" will be quite different with an 8 point font versus a 72 point font, for example.

    It might also help to convert the calculated CGRect into an integral rect which will round up any fractional sizes. Use the integral property of CGRect.