Re: Is it possible to animate a path similar to how StrokeEnd works in SpriteKit ?

Squillop, yes you can animate SKShapeNode's path by supplying a custom strokeShader that outputs based on a few of SKShader's properties, v_path_distance and u_path_length. Note that within the shader supplied below "u_current_percentage" is added by us and refers to the current point within the path we want stroked up to. By that, the scene determines the pace of the animated stroking. Also note that strokeShader being a fragment shader, outputs an RGB at every step, it allows you to control the color as you go, allowing the stroke to be a gradient color for example.

The shader is added as a file to the Xcode project "animateStroke.fsh":

void main()
{
    if ( u_path_length == 0.0 ) {
        gl_FragColor = vec4( 0.0, 0.0, 1.0, 1.0 ); 
    } else if ( v_path_distance / u_path_length <= u_current_percentage ) {
        gl_FragColor = vec4( 1.0, 0.0, 0.0, 1.0 ); 
    } else {
        gl_FragColor = vec4( 0.0, 0.0, 0.0, 0.0 ); 
    }
}

And the sample SKScene subclass using it:

import SpriteKit
import GameplayKit
func shaderWithFilename( _ filename: String?, fileExtension: String?, uniforms: [SKUniform] ) -> SKShader {
    let path = Bundle.main.path( forResource: filename, ofType: fileExtension )
    let source = try! NSString( contentsOfFile: path!, encoding: String.Encoding.utf8.rawValue )
    let shader = SKShader( source: source as String, uniforms: uniforms )
    return shader
}
class GameScene: SKScene {
    let strokeSizeFactor = CGFloat( 2.0 )
    var strokeShader: SKShader!
    var strokeLengthUniform: SKUniform!
    var _strokeLengthFloat: Float = 0.0
    var strokeLengthKey: String!
    var strokeLengthFloat: Float {
        get {
            return _strokeLengthFloat
        }
        set( newStrokeLengthFloat ) {
            _strokeLengthFloat = newStrokeLengthFloat
            strokeLengthUniform.floatValue = newStrokeLengthFloat
        }
    }

    override func didMove(to view: SKView) {
        strokeLengthKey = "u_current_percentage"
        strokeLengthUniform = SKUniform( name: strokeLengthKey, float: 0.0 )
        let uniforms: [SKUniform] = [strokeLengthUniform]
        strokeShader = shaderWithFilename( "animateStroke", fileExtension: "fsh", uniforms: uniforms )
        strokeLengthFloat = 0.0
        let cameraNode = SKCameraNode()
        self.camera = cameraNode
        let strokeHeight = CGFloat( 200 ) * strokeSizeFactor
        let path1 = CGMutablePath()
        path1.move( to: CGPoint.zero )
        path1.addLine( to: CGPoint( x: 0, y: strokeHeight ) )

        // prior to a fix in iOS 10.2, bug #27989113  "SKShader/SKShapeNode: u_path_length is not set unless shouldUseLocalStrokeBuffers() is true"
        // add a few points to work around this bug in iOS 10-10.1 ->
        // for i in 0...15 {
        //    path1.addLine( to: CGPoint( x: 0, y: strokeHeight + CGFloat( 0.001 ) * CGFloat( i ) ) )
        // }

        path1.closeSubpath()
        let strokeWidth = 17.0 * strokeSizeFactor
        let path2 = CGMutablePath()
        path2.move( to: CGPoint.zero )
        path2.addLine( to: CGPoint( x: 0, y: strokeHeight ) )
        path2.closeSubpath()
        let backgroundShapeNode = SKShapeNode( path: path2 )
        backgroundShapeNode.lineWidth = strokeWidth
        backgroundShapeNode.zPosition = 5.0
        backgroundShapeNode.lineCap = .round
        backgroundShapeNode.strokeColor = SKColor.darkGray
        addChild( backgroundShapeNode )

        let shapeNode = SKShapeNode( path: path1 )
        shapeNode.lineWidth = strokeWidth
        shapeNode.lineCap = .round
        backgroundShapeNode.addChild( shapeNode )
        shapeNode.addChild( cameraNode )
        shapeNode.strokeShader = strokeShader
        backgroundShapeNode.calculateAccumulatedFrame()

        cameraNode.position = CGPoint( x: backgroundShapeNode.frame.size.width/2.0, y: backgroundShapeNode.frame.size.height/2.0 )            
    }

    override func update(_ currentTime: TimeInterval) {      
        // the increment chosen determines how fast the path is stroked. Note this maps to "u_current_percentage" within animateStroke.fsh
        strokeLengthFloat += 0.01
        if strokeLengthFloat > 1.0 {
            strokeLengthFloat = 0.0
        }      
    }
}