VideoLabel-mask.swift

private func generateTextMask() -> CGImage? {
    guard frame.size.width != 0.0,
        frame.size.height != 0.0,
        let attributedString = maskAttributedText() else {
        return nil
    }

    let bitmap = Bitmap(width: frame.size.width, height: frame.size.height)

    bitmap.context.clear(bitmap.bounds)
   
    let framesetter = CTFramesetterCreateWithAttributedString(attributedString)
    let range = CFRange(location: 0, length: attributedString.length)
    var effectiveRange: CFRange = .init(location: 0, length: 0)
    let suggestedSize = CTFramesetterSuggestFrameSizeWithConstraints(framesetter, range, nil, bitmap.bounds.size, &effectiveRange)
    
    if effectiveRange.length < range.length {
        print("VideoLabel ERROR: The view's frame is too small to display the full text.")
    }
    
    let path = CGMutablePath()
    let bitmapBounds = bitmap.bounds
    
    let textRect: CGRect
    
    let alignment = textAlignment(for: attributedString)
    
    switch alignment {
    case .left, .natural:
        textRect = CGRect(x: 0.0,
                          y: (bitmapBounds.size.height - suggestedSize.height) * 0.5,
                          width: suggestedSize.width,
                          height: suggestedSize.height)
        
    case .right:
        textRect = CGRect(x: bitmapBounds.size.width - suggestedSize.width,
                          y: (bitmapBounds.size.height - suggestedSize.height) * 0.5,
                          width: suggestedSize.width,
                          height: suggestedSize.height)
        
    case .justified, .center:
        textRect = CGRect(x: (bitmapBounds.size.width - suggestedSize.width) * 0.5,
                          y: (bitmapBounds.size.height - suggestedSize.height) * 0.5,
                          width: suggestedSize.width,
                          height: suggestedSize.height)
    @unknown default:
        textRect = CGRect(x: (bitmapBounds.size.width - suggestedSize.width) * 0.5,
                          y: (bitmapBounds.size.height - suggestedSize.height) * 0.5,
                          width: suggestedSize.width,
                          height: suggestedSize.height)
    }
    
    path.addRect(textRect)
    let textRectInViewSpace = CGRect(x: textRect.origin.x / Bitmap.contentScale,
                                     y: textRect.origin.y / Bitmap.contentScale,
                                     width: textRect.size.width / Bitmap.contentScale,
                                     height: textRect.size.height / Bitmap.contentScale)
    let textRectInScreenSpace = UIAccessibility.convertToScreenCoordinates(textRectInViewSpace, in: self)
    accessibilityFrame = textRectInScreenSpace
    
    let ctFrame = CTFramesetterCreateFrame(framesetter, CFRange(location: 0, length: CFIndex(attributedString.length)), path, nil)

    CTFrameDraw(ctFrame, bitmap.context)
    
    return bitmap.cgImage
}