Reduce default minimum frame rate to 20 fps

[1ec5]

Reduced the default minimum frame rate (on battery power away from maneuvers) from 30 fps to 20 fps for improved battery performance. The frame rate while plugged in remains 30 fps, and the frame rate during the 10 seconds around a maneuver remains at 60 fps or 120 fps, depending on the device.

/cc @frederoni @JThramer

[frederoni]

👍
>= 20 should be above the uncanny valley for most pair of eyes.

[1ec5]

Just to give a crude sense of the performance improvement, I simulated a half-mile-long (2-minute-long) route along surface streets while on battery power on an iPhone 8 running iOS 12. Over 20 seconds of straightaway, away from maneuvers, the Swift example application posted these times:

Frame rate	CPU time	% of control	Notes
30fps	4.41 s	100%	344de5e (master)
20fps	3.04 s	68.9%	This PR
5fps	1.10 s	24.9%	Equivalent to before #1749

Overall, for the entire duration of the session (including the flying animation at the beginning), we posted these times:

Frame rate	CPU time	% of control	Notes
30fps	44.48 s	100%	344de5e
20fps	37.46 s	84.2%	This PR
5fps	23.28 s	52.3%	Equivalent to before #1749

[1ec5]

For reference, I rigged a couple more test runs with some additional variations to the map style to illustrate the impact that they can have:

Setup	Straightaway	%	Trip	%
This PR	3.04 s	100%	37.46 s	100%
Night	3.04 s	100%	33.43 s	100%
No symbols	2.31 s	76.0%	24.52 s	65.5%
Blank	1.61 s	53.0%	19.72 s	52.6%

No symbols

diff --git a/MapboxNavigation/NavigationMapView.swift b/MapboxNavigation/NavigationMapView.swift
index 8cb35c71..760cbf83 100644
--- a/MapboxNavigation/NavigationMapView.swift
+++ b/MapboxNavigation/NavigationMapView.swift
@@ -968,31 +968,8 @@ open class NavigationMapView: MGLMapView, UIGestureRecognizerDelegate {
             return
         }
         
-        let streetsSourceIdentifiers: [String] = style.sources.compactMap {
-            $0 as? MGLVectorTileSource
-        }.filter {
-            $0.isMapboxStreets
-        }.map {
-            $0.identifier
-        }
-        
         for layer in style.layers where layer is MGLSymbolStyleLayer {
-            let layer = layer as! MGLSymbolStyleLayer
-            guard let sourceIdentifier = layer.sourceIdentifier,
-                streetsSourceIdentifiers.contains(sourceIdentifier) else {
-                continue
-            }
-            guard let text = layer.text else {
-                continue
-            }
-            
-            // Road labels should match road signage.
-            let locale = layer.sourceLayerIdentifier == "road_label" ? Locale(identifier: "mul") : nil
-            
-            let localizedText = text.mgl_expressionLocalized(into: locale)
-            if localizedText != text {
-                layer.text = localizedText
-            }
+            style.removeLayer(layer)
         }
     }
     

Blank

diff --git a/Examples/Swift/ViewController.swift b/Examples/Swift/ViewController.swift
index fa1a7ce9..f80defb6 100644
--- a/Examples/Swift/ViewController.swift
+++ b/Examples/Swift/ViewController.swift
@@ -282,7 +282,7 @@ extension ViewController: MGLMapViewDelegate {
             return
         }
         
-        self.mapView?.localizeLabels()
+//        self.mapView?.localizeLabels()
         
         if let routes = routes, let currentRoute = routes.first, let coords = currentRoute.coordinates {
             mapView.setVisibleCoordinateBounds(MGLPolygon(coordinates: coords, count: currentRoute.coordinateCount).overlayBounds, animated: false)
diff --git a/MapboxNavigation/NavigationMapView.swift b/MapboxNavigation/NavigationMapView.swift
index 8cb35c71..5eb5f5cf 100644
--- a/MapboxNavigation/NavigationMapView.swift
+++ b/MapboxNavigation/NavigationMapView.swift
@@ -968,31 +968,8 @@ open class NavigationMapView: MGLMapView, UIGestureRecognizerDelegate {
             return
         }
         
-        let streetsSourceIdentifiers: [String] = style.sources.compactMap {
-            $0 as? MGLVectorTileSource
-        }.filter {
-            $0.isMapboxStreets
-        }.map {
-            $0.identifier
-        }
-        
-        for layer in style.layers where layer is MGLSymbolStyleLayer {
-            let layer = layer as! MGLSymbolStyleLayer
-            guard let sourceIdentifier = layer.sourceIdentifier,
-                streetsSourceIdentifiers.contains(sourceIdentifier) else {
-                continue
-            }
-            guard let text = layer.text else {
-                continue
-            }
-            
-            // Road labels should match road signage.
-            let locale = layer.sourceLayerIdentifier == "road_label" ? Locale(identifier: "mul") : nil
-            
-            let localizedText = text.mgl_expressionLocalized(into: locale)
-            if localizedText != text {
-                layer.text = localizedText
-            }
+        for layer in style.layers {
+            style.removeLayer(layer)
         }
     }