How do you add MKPolylines to MKSnapShotter in swift 3? - ios

Question

Is there a way to take a screenshot of mapView and include the polyline? I believe I need to draw CGPoint's on the image that the MKSnapShotter returns, but I am unsure on how to do so.
Current code
func takeSnapshot(mapView: MKMapView, withCallback: (UIImage?, NSError?) -> ()) {
let options = MKMapSnapshotOptions()
options.region = mapView.region
options.size = mapView.frame.size
options.scale = UIScreen.main().scale
let snapshotter = MKMapSnapshotter(options: options)
snapshotter.start() { snapshot, error in
guard snapshot != nil else {
withCallback(nil, error)
return
}
if let image = snapshot?.image{
withCallback(image, nil)
for coordinate in self.area {
image.draw(at:snapshot!.point(for: coordinate))
}
}
}
}

Answer 1

I had the same problem today. After several hours of research, here is how I solve it.
The following codes are in Swift 3.
1. Init your polyline coordinates array
// initial this array with your polyline coordinates
var yourCoordinates = [CLLocationCoordinate2D]()
yourCoorinates.append( coordinate 1 )
yourCoorinates.append( coordinate 2 )
...
// you can use any data structure you like
2. take the snapshot as usual, but set the region based on your coordinates:
func takeSnapShot() {
let mapSnapshotOptions = MKMapSnapshotOptions()
// Set the region of the map that is rendered. (by polyline)
let polyLine = MKPolyline(coordinates: &yourCoordinates, count: yourCoordinates.count)
let region = MKCoordinateRegionForMapRect(polyLine.boundingMapRect)
mapSnapshotOptions.region = region
// Set the scale of the image. We'll just use the scale of the current device, which is 2x scale on Retina screens.
mapSnapshotOptions.scale = UIScreen.main.scale
// Set the size of the image output.
mapSnapshotOptions.size = CGSize(width: IMAGE_VIEW_WIDTH, height: IMAGE_VIEW_HEIGHT)
// Show buildings and Points of Interest on the snapshot
mapSnapshotOptions.showsBuildings = true
mapSnapshotOptions.showsPointsOfInterest = true
let snapShotter = MKMapSnapshotter(options: mapSnapshotOptions)
snapShotter.start() { snapshot, error in
guard let snapshot = snapshot else {
return
}
// Don't just pass snapshot.image, pass snapshot itself!
self.imageView.image = self.drawLineOnImage(snapshot: snapshot)
}
}
3. Use snapshot.point() to draw Polylines on Snapshot Image
func drawLineOnImage(snapshot: MKMapSnapshot) -> UIImage {
let image = snapshot.image
// for Retina screen
UIGraphicsBeginImageContextWithOptions(self.imageView.frame.size, true, 0)
// draw original image into the context
image.draw(at: CGPoint.zero)
// get the context for CoreGraphics
let context = UIGraphicsGetCurrentContext()
// set stroking width and color of the context
context!.setLineWidth(2.0)
context!.setStrokeColor(UIColor.orange.cgColor)
// Here is the trick :
// We use addLine() and move() to draw the line, this should be easy to understand.
// The diificult part is that they both take CGPoint as parameters, and it would be way too complex for us to calculate by ourselves
// Thus we use snapshot.point() to save the pain.
context!.move(to: snapshot.point(for: yourCoordinates[0]))
for i in 0...yourCoordinates.count-1 {
context!.addLine(to: snapshot.point(for: yourCoordinates[i]))
context!.move(to: snapshot.point(for: yourCoordinates[i]))
}
// apply the stroke to the context
context!.strokePath()
// get the image from the graphics context
let resultImage = UIGraphicsGetImageFromCurrentImageContext()
// end the graphics context
UIGraphicsEndImageContext()
return resultImage!
}
That's it, hope this helps someone.
References
How do I draw on an image in Swift?
MKTile​Overlay,MKMap​Snapshotter & MKDirections
Creating an MKMapSnapshotter with an MKPolylineRenderer
Render a Map as an Image using MapKit

Answer 2

What is wrong with:
snapshotter.start( completionHandler: { snapshot, error in
guard snapshot != nil else {
withCallback(nil, error)
return
}
if let image = snapshot?.image {
withCallback(image, nil)
for coordinate in self.area {
image.draw(at:snapshot!.point(for: coordinate))
}
}
})

Answer 3

If you just want a copy of the image the user sees in the MKMapView, remember that it's a UIView subclass, and so you could do this...
public extension UIView {
public var snapshot: UIImage? {
get {
UIGraphicsBeginImageContextWithOptions(self.bounds.size, false, UIScreen.main.scale)
self.drawHierarchy(in: self.bounds, afterScreenUpdates: true)
let image = UIGraphicsGetImageFromCurrentImageContext()
UIGraphicsEndImageContext()
return image
}
}
}
// ...
if let img = self.mapView.snapshot {
// Do something
}