iOS Heatmap Example using runtime styling and clustering

ios_heatmap_example.md

    
    // Ported from https://www.mapbox.com/mapbox-gl-js/example/heatmap/
  
    func mapViewDidFinishLoadingMap(_ mapView: MGLMapView) {
        let source = MGLSource(identifier: "source")

        let symbolLayer = MGLSymbolStyleLayer(identifier: "place-city-sm", source: source)
        let url = URL(string: "https://www.mapbox.com/mapbox-gl-js/assets/earthquakes.geojson")!
        let options = [MGLShapeSourceOption.clustered: NSNumber(booleanLiteral: true),
                       MGLShapeSourceOption.clusterRadius: NSNumber(integerLiteral: 20),
                       MGLShapeSourceOption.maximumZoomLevel: NSNumber(integerLiteral: 15)]
        let shapeSource = MGLShapeSource(identifier: "earthquakes", url: url, options: options)
        mapView.style?.addSource(shapeSource)

        let unclusteredLayer = MGLCircleStyleLayer(identifier: "unclustered", source: shapeSource)
        unclusteredLayer.circleColor = MGLStyleValue(rawValue: UIColor(colorLiteralRed: 229/255.0, green: 94/255.0, blue: 94/255.0, alpha: 1))
        unclusteredLayer.circleRadius = MGLStyleValue(rawValue: NSNumber(integerLiteral: 20))
        unclusteredLayer.circleBlur = MGLStyleValue(rawValue: NSNumber(integerLiteral: 15))
        unclusteredLayer.predicate = NSPredicate(format: "%K != YES", argumentArray: ["cluster"])
        mapView.style?.insertLayer(unclusteredLayer, below: symbolLayer)

        let layers = [[NSNumber(floatLiteral: 150.0), UIColor(colorLiteralRed: 229/255.0, green: 94/255.0, blue: 94/255.0, alpha: 1)],
                      [NSNumber(floatLiteral: 20.0), UIColor(colorLiteralRed: 249/255.0, green: 136/255.0, blue: 108/255.0, alpha: 1)],
                      [NSNumber(floatLiteral: 0.0), UIColor(colorLiteralRed: 251/255.0, green: 176/255.0, blue: 59/255.0, alpha: 1)]]

        for index in 0..<layers.count {
            let circles = MGLCircleStyleLayer(identifier: "cluster-\(index)", source: shapeSource)
            circles.circleColor = MGLStyleValue(rawValue: layers[index][1] as! UIColor)
            circles.circleRadius = MGLStyleValue(rawValue: NSNumber(integerLiteral: 70))
            circles.circleBlur = MGLStyleValue(rawValue: NSNumber(integerLiteral: 1))

            let gtePredicate = NSPredicate(format: "%K >= %@", argumentArray: ["point_count", layers[index][0] as! NSNumber])
            let allPredicate = index == 0 ?
                gtePredicate :
                NSCompoundPredicate(andPredicateWithSubpredicates: [gtePredicate, NSPredicate(format: "%K < %@", argumentArray: ["point_count", layers[index - 1][0] as! NSNumber])])

            circles.predicate = allPredicate

            mapView.style?.insertLayer(circles, below: symbolLayer)
        }
    }