MKPolyline strange rendering related with zooming in MapKit

Question

I have very simple View Controller to demonstrate this strange rendering behavior of MKPolyline. Nothing special just normal api calls.

import UIKit
import MapKi         


        

Answer 1

Swift 3 solution :

Create a subclass of MKPolylineRenderer

class CustomPolyline: MKPolylineRenderer {

    override func applyStrokeProperties(to context: CGContext, atZoomScale zoomScale: MKZoomScale) {
        super.applyStrokeProperties(to: context, atZoomScale: zoomScale)
        UIGraphicsPushContext(context)
        if let ctx = UIGraphicsGetCurrentContext() {
            ctx.setLineWidth(self.lineWidth)
        }
    }
}

Then use it in your rendererFor MapKit delegate :

func mapView(_ mapView: MKMapView, rendererFor overlay: MKOverlay) -> MKOverlayRenderer {
        let renderer = CustomPolyline(overlay: overlay)
        renderer.strokeColor = UIColor.red
        renderer.lineWidth = 100
        return renderer
}

Your polylines won't re-render after zooming thus avoiding the artifacts