Fix scale bar incorrect scale.

app/build.gradle

@@ -65,6 +65,7 @@ dependencies {
     exclude group: 'com.google.android.gms'
   })
   implementation dependenciesList.mapboxGeocoding
+  implementation dependenciesList.mapboxTurf
 
   // Architecture
   implementation dependenciesList.lifecycleExtensions

app/src/main/java/com/mapbox/mapboxsdk/plugins/testapp/activity/scalebar/ScalebarActivity.kt

@@ -3,12 +3,23 @@ package com.mapbox.mapboxsdk.plugins.testapp.activity.scalebar
 import android.os.Bundle
 import android.support.v7.app.AppCompatActivity
 import com.mapbox.mapboxsdk.maps.MapboxMap
+import com.mapbox.turf.TurfMeasurement
 import com.mapbox.mapboxsdk.maps.Style
 import com.mapbox.mapboxsdk.plugins.testapp.R
 import com.mapbox.pluginscalebar.ScaleBarOptions
 import com.mapbox.pluginscalebar.ScaleBarPlugin
 import kotlinx.android.synthetic.main.activity_scalebar.*
 
+import com.mapbox.geojson.LineString
+import com.mapbox.geojson.Point
+
+import com.mapbox.mapboxsdk.style.layers.LineLayer
+
+import com.mapbox.mapboxsdk.style.sources.GeoJsonSource
+import com.mapbox.turf.TurfConstants
+
+import java.util.*
+
 /**
  * Activity showing a scalebar used on a MapView.
  */
@@ -20,6 +31,7 @@ class ScalebarActivity : AppCompatActivity() {
         mapView.getMapAsync { mapboxMap ->
             mapboxMap.setStyle(Style.MAPBOX_STREETS) {
                 addScalebar(mapboxMap)
+                setupTestLine(it)
             }
         }
     }
@@ -43,6 +55,17 @@ class ScalebarActivity : AppCompatActivity() {
         }
     }
 
+    private fun setupTestLine(style: Style) {
+        val source = GeoJsonSource("source-id")
+        val lineLayer = LineLayer("layer-id", source.id)
+        val startPoint: Point = Point.fromLngLat(-122.447244, 37.769145)
+        val endPoint: Point = TurfMeasurement.destination(startPoint, 200.0, 90.0, TurfConstants.UNIT_METERS)
+        val pointList: List<Point> = listOf(startPoint, endPoint)
+        source.setGeoJson(LineString.fromLngLats(pointList))
+        style.addSource(source)
+        style.addLayer(lineLayer)
+    }
+
     override fun onStart() {
         super.onStart()
         mapView.onStart()

app/src/main/res/layout/activity_scalebar.xml

@@ -12,7 +12,7 @@
         android:layout_height="match_parent"
         app:mapbox_cameraTargetLat="37.769145"
         app:mapbox_cameraTargetLng="-122.447244"
-        app:mapbox_cameraZoom="9" />
+        app:mapbox_cameraZoom="15.5" />
 
     <android.support.design.widget.FloatingActionButton
         android:id="@+id/fabScaleWidget"

gradle/dependencies.gradle

@@ -9,6 +9,7 @@
   version = [
       mapboxMapSdk       : '8.6.0',
       mapboxJava         : '4.9.0',
+      mapboxTurf         : '4.9.0',
       playLocation       : '16.0.0',
       autoValue          : '1.5.4',
       autoValueParcel    : '0.2.6',
@@ -32,7 +33,7 @@
   pluginVersion = [
       checkstyle: '8.10.1',
       gradle    : '3.4.0',
-      kotlin    : '1.3.20',
+      kotlin    : '1.3.50',
       dokka     : '0.9.17',
       kotlinLint: '8.1.0'
   ]
@@ -42,6 +43,7 @@
       mapboxMapSdk           : "com.mapbox.mapboxsdk:mapbox-android-sdk:${version.mapboxMapSdk}",
       mapboxGeoJson          : "com.mapbox.mapboxsdk:mapbox-sdk-geojson:${version.mapboxJava}",
       mapboxGeocoding        : "com.mapbox.mapboxsdk:mapbox-sdk-services:${version.mapboxJava}",
+      mapboxTurf             : "com.mapbox.mapboxsdk:mapbox-sdk-turf:${version.mapboxTurf}",
 
       // Google Play Location
       playLocation           : "com.google.android.gms:play-services-location:${version.playLocation}",

plugin-scalebar/src/main/java/com/mapbox/pluginscalebar/ScaleBarPlugin.java

@@ -107,7 +107,8 @@ public void setEnabled(boolean enabled) {
 
   private void invalidateScaleBar() {
     CameraPosition cameraPosition = mapboxMap.getCameraPosition();
-    scaleBarWidget.setDistancePerPixel(projection.getMetersPerPixelAtLatitude(cameraPosition.target.getLatitude()));
+    scaleBarWidget.setDistancePerPixel((projection.getMetersPerPixelAtLatitude(cameraPosition.target.getLatitude()))
+      / mapView.getContext().getResources().getDisplayMetrics().density);
   }
 
   private void addCameraListeners() {

plugin-scalebar/src/test/java/com/mapbox/pluginscalebar/ScaleBarPluginTest.kt

@@ -1,5 +1,8 @@
 package com.mapbox.pluginscalebar
 
+import android.content.Context
+import android.content.res.Resources
+import android.util.DisplayMetrics
 import android.view.View
 import com.mapbox.mapboxsdk.camera.CameraPosition
 import com.mapbox.mapboxsdk.maps.MapView
@@ -8,6 +11,7 @@ import com.mapbox.mapboxsdk.maps.Projection
 import io.mockk.MockKAnnotations
 import io.mockk.every
 import io.mockk.impl.annotations.MockK
+import io.mockk.spyk
 import io.mockk.verify
 import org.junit.Assert.*
 import org.junit.Before
@@ -29,14 +33,25 @@ class ScaleBarPluginTest {
   @MockK
   lateinit var scaleBarWidget: ScaleBarWidget
 
+  @MockK
+  lateinit var context: Context
+
+  @MockK
+  lateinit var resources: Resources
+  @MockK
+  lateinit var displayMetrics: DisplayMetrics
   @Before
   fun setUp() {
     MockKAnnotations.init(this, relaxUnitFun = true)
+    displayMetrics.density = 2f
     every { mapView.width } returns 1000
     every { projection.getMetersPerPixelAtLatitude(CameraPosition.DEFAULT.target.latitude) } returns 100_000.0
     every { mapboxMap.projection } returns projection
     every { mapboxMap.cameraPosition } returns CameraPosition.DEFAULT
     every { scaleBarOptions.build() } returns scaleBarWidget
+    every { mapView.context} returns context
+    every { context.resources} returns resources
+    every { resources.displayMetrics} returns displayMetrics
   }
 
   @Test
@@ -113,11 +128,11 @@ class ScaleBarPluginTest {
     val scaleBarPlugin = ScaleBarPlugin(mapView, mapboxMap)
     scaleBarPlugin.create(scaleBarOptions)
     verify(exactly = 1) { mapboxMap.cameraPosition }
-    verify(exactly = 1) { scaleBarWidget.setDistancePerPixel(100_000.0) }
+    verify(exactly = 1) { scaleBarWidget.setDistancePerPixel(50_000.0) }
     scaleBarPlugin.isEnabled = false
     scaleBarPlugin.isEnabled = true
 
     verify(exactly = 2) { mapboxMap.cameraPosition }
-    verify(exactly = 2) { scaleBarWidget.setDistancePerPixel(100_000.0) }
+    verify(exactly = 2) { scaleBarWidget.setDistancePerPixel(50_000.0) }
   }
 }