user594883 user594883 - 6 months ago 62
Swift Question

Swift: How to add points to a closed CGPath?

I'd like to make SKSpriteNodes to move along letter outlines. I have many letters but here's one example:

enter image description here

I would like the sprite to follow the red line. I found this answer that mostly covers my problem: Get path to trace out a character in an iOS UIFont

The answer comes with this good and working example code:

let font = UIFont(name: "HelveticaNeue", size: 64)!


var unichars = [UniChar]("P".utf16)
var glyphs = [CGGlyph](count: unichars.count, repeatedValue: 0)
let gotGlyphs = CTFontGetGlyphsForCharacters(font, &unichars, &glyphs, unichars.count)
if gotGlyphs {
let cgpath = CTFontCreatePathForGlyph(font, glyphs[0], nil)!
let path = UIBezierPath(CGPath: cgpath)
print(path)
XCPlaygroundPage.currentPage.captureValue(path, withIdentifier: "glyph \(glyphs[0])")
}


However I still run into a problem as my sprite doesn't complete full path around the letter for all the letters but instead e.g. with "P" stops here (and started from the bottom):

enter image description here

I tried adding some points to the
path
like so:

CGPathAddLineToPoint(path, nil, 0, 0)


but the result doesn't work probably because the added point is after the
<Close>
statement:

<UIBezierPath: 0x7889ff70; <MoveTo {25.950001, 55.800003}>,
<LineTo {25.950001, 95.100006}>,
<LineTo {53.850002, 95.100006}>,
<QuadCurveTo {71.625, 90.075005} - {66, 95.100006}>,
<QuadCurveTo {77.25, 75.450005} - {77.25, 85.050003}>,
<QuadCurveTo {71.625, 60.750004} - {77.25, 65.850006}>,
<QuadCurveTo {53.850002, 55.800003} - {66, 55.650002}>,
<Close>,
<MoveTo {11.700001, 107.10001}>,
<LineTo {11.700001, 0}>,
<LineTo {25.950001, 0}>,
<LineTo {25.950001, 43.800003}>,
<LineTo {58.650002, 43.800003}>,
<QuadCurveTo {83.175003, 52.050003} - {74.850006, 43.650002}>,
<QuadCurveTo {91.5, 75.450005} - {91.5, 60.450001}>,
<QuadCurveTo {83.175003, 98.775002} - {91.5, 90.450005}>,
<QuadCurveTo {58.650002, 107.10001} - {74.850006, 107.10001}>,
<Close>,
<LineTo {0, 0}>

Answer

First of all you need a method to retrieve all elements from CGPath.

I've translated to Swift this method (you find also an example to how to use it).

As I can see here in your code, you need also to know what kinds of element compose your path, but CGPathElement work with UnsafeMutablePointer<CGPoint> (it can be not confortable), so you can modify my translation by creating a function with two output arrays like this:

//MARK: - CGPath extensions
extension CGPath {
    func getPathElementsPointsAndTypes() -> ([CGPoint],[CGPathElementType]) {
            var arrayPoints : [CGPoint]! = [CGPoint]()
            var arrayTypes : [CGPathElementType]! = [CGPathElementType]()
            self.forEach { element in
                switch (element.type) {
                case CGPathElementType.MoveToPoint:
                    arrayPoints.append(element.points[0])
                    arrayTypes.append(element.type)
                case .AddLineToPoint:
                    arrayPoints.append(element.points[0])
                    arrayTypes.append(element.type)
                case .AddQuadCurveToPoint:
                    arrayPoints.append(element.points[0])
                    arrayPoints.append(element.points[1])
                    arrayTypes.append(element.type)
                    arrayTypes.append(element.type)
                case .AddCurveToPoint:
                    arrayPoints.append(element.points[0])
                    arrayPoints.append(element.points[1])
                    arrayPoints.append(element.points[2])
                    arrayTypes.append(element.type)
                    arrayTypes.append(element.type)
                    arrayTypes.append(element.type)
                default: break
                }
            }
            return (arrayPoints,arrayTypes)
    }
}

After that you have a array of points and a specular array of type that explain what type is each point in our list. This time all closePath are removed.

Now it's time to re-create path ad HOC for you situation:

func createNewPath(path:CGPath) -> UIBezierPath {
        let (points,types) = path.getPathElementsPointsAndTypes()
        if points.count <= 1 {
            return  UIBezierPath() // exit
        }

        let pathRef = UIBezierPath()
        var i = 0
        while i < points.count {
            switch (types[i]) {
                case CGPathElementType.MoveToPoint:
                    pathRef.moveToPoint(CGPointMake(points[i].x,points[i].y))
                case .AddLineToPoint:
                    pathRef.addLineToPoint(CGPointMake(points[i].x,points[i].y))
                case .AddQuadCurveToPoint:
                    pathRef.addQuadCurveToPoint(CGPointMake(points[i].x,points[i].y), controlPoint: CGPointMake(points[i+1].x,points[i+1].y))
                    i += 1
                case .AddCurveToPoint:
                    pathRef.addCurveToPoint(CGPointMake(points[i].x,points[i].y), controlPoint1: CGPointMake(points[i+1].x,points[i+1].y), controlPoint2: CGPointMake(points[i+2].x,points[i+2].y))
                    i += 2
            default: break
            }
            i += 1
        }
        //pathRef.closePath() if you want to add new elements dont uncomment this
        return pathRef
    }

After launching this method, you will have your path cleaned by all closePath and ready to add new lines as you wish.