Add api and demo for expression distance (#339)

* Add api and demo for expression distance

* Update test case

MapboxGLAndroidSDKTestApp/src/main/AndroidManifest.xml

@@ -515,6 +515,18 @@
                 android:name="android.support.PARENT_ACTIVITY"
                 android:value=".activity.FeatureOverviewActivity" />
         </activity>
+        <activity
+            android:name=".activity.style.DistanceExpressionActivity"
+            android:description="@string/description_distance_style"
+            android:exported="true"
+            android:label="@string/activity_distance_style">
+            <meta-data
+                android:name="@string/category"
+                android:value="@string/category_style" />
+            <meta-data
+                android:name="android.support.PARENT_ACTIVITY"
+                android:value=".activity.FeatureOverviewActivity" />
+        </activity>
         <activity
             android:name=".activity.style.GradientLineActivity"
             android:description="@string/description_gradient_line"

MapboxGLAndroidSDKTestApp/src/main/java/com/mapbox/mapboxsdk/testapp/activity/style/DistanceExpressionActivity.kt

@@ -0,0 +1,129 @@
+package com.mapbox.mapboxsdk.testapp.activity.style
+
+import android.graphics.Color
+import android.os.Bundle
+import android.os.PersistableBundle
+import androidx.appcompat.app.AppCompatActivity
+import com.mapbox.geojson.Point
+import com.mapbox.mapboxsdk.camera.CameraPosition
+import com.mapbox.mapboxsdk.geometry.LatLng
+import com.mapbox.mapboxsdk.maps.MapboxMap
+import com.mapbox.mapboxsdk.maps.Style
+import com.mapbox.mapboxsdk.style.expressions.Expression.distance
+import com.mapbox.mapboxsdk.style.expressions.Expression.lt
+import com.mapbox.mapboxsdk.style.layers.FillLayer
+import com.mapbox.mapboxsdk.style.layers.Property.NONE
+import com.mapbox.mapboxsdk.style.layers.PropertyFactory.*
+import com.mapbox.mapboxsdk.style.layers.SymbolLayer
+import com.mapbox.mapboxsdk.style.sources.GeoJsonSource
+import com.mapbox.mapboxsdk.testapp.R
+import com.mapbox.turf.TurfConstants
+import com.mapbox.turf.TurfTransformation
+import kotlinx.android.synthetic.main.activity_physical_circle.*
+
+/**
+ * An Activity that showcases the within expression to filter features outside a geometry
+ */
+class DistanceExpressionActivity : AppCompatActivity() {
+
+  private lateinit var mapboxMap: MapboxMap
+
+  private val lat = 37.78794572301525
+  private val lon = -122.40752220153807
+
+  override fun onCreate(savedInstanceState: Bundle?) {
+    super.onCreate(savedInstanceState)
+    setContentView(R.layout.activity_within_expression)
+
+    mapView.onCreate(savedInstanceState)
+    mapView.getMapAsync { map ->
+      mapboxMap = map
+
+      // Setup camera position above Georgetown
+      mapboxMap.cameraPosition = CameraPosition.Builder()
+        .target(LatLng(lat, lon))
+        .zoom(16.0)
+        .build()
+      setupStyle()
+    }
+  }
+
+  private fun setupStyle() {
+    val center = Point.fromLngLat(lon, lat)
+    val circle = TurfTransformation.circle(center, 150.0, TurfConstants.UNIT_METRES)
+    // Setup style with additional layers,
+    // using Style.MAPBOX_STREETS as a base style
+    mapboxMap.setStyle(
+      Style.Builder()
+        .fromUri(Style.MAPBOX_STREETS)
+        .withSources(
+          GeoJsonSource(
+            POINT_ID, Point.fromLngLat(lon, lat)
+          ),
+          GeoJsonSource(CIRCLE_ID, circle)
+        )
+        .withLayerBelow(
+          FillLayer(CIRCLE_ID, CIRCLE_ID)
+            .withProperties(
+              fillOpacity(0.5f),
+              fillColor(Color.parseColor("#3bb2d0"))
+            ), "poi-label"
+        )
+    ) { style ->
+      // Show only POI labels inside circle radius using distance expression
+      val symbolLayer = style.getLayer("poi-label") as SymbolLayer
+      symbolLayer.setFilter(lt(
+        distance(
+          Point.fromLngLat(lon, lat), "meters"
+        ), 150)
+      )
+
+      // Hide other types of labels to highlight POI labels
+      (style.getLayer("road-label") as SymbolLayer).setProperties(visibility(NONE))
+      (style.getLayer("transit-label") as SymbolLayer).setProperties(visibility(NONE))
+      (style.getLayer("road-number-shield") as SymbolLayer).setProperties(visibility(NONE))
+    }
+  }
+
+  override fun onStart() {
+    super.onStart()
+    mapView.onStart()
+  }
+
+  override fun onResume() {
+    super.onResume()
+    mapView.onResume()
+  }
+
+  override fun onPause() {
+    super.onPause()
+    mapView.onPause()
+  }
+
+  override fun onStop() {
+    super.onStop()
+    mapView.onStop()
+  }
+
+  override fun onLowMemory() {
+    super.onLowMemory()
+    mapView.onLowMemory()
+  }
+
+  override fun onDestroy() {
+    super.onDestroy()
+    mapView.onDestroy()
+  }
+
+  override fun onSaveInstanceState(outState: Bundle?, outPersistentState: PersistableBundle?) {
+    super.onSaveInstanceState(outState, outPersistentState)
+    outState?.let {
+      mapView.onSaveInstanceState(it)
+    }
+  }
+
+  companion object {
+    const val POINT_ID = "point"
+    const val CIRCLE_ID = "circle"
+  }
+}

MapboxGLAndroidSDKTestApp/src/main/res/values/descriptions.xml

@@ -34,6 +34,7 @@
     <string name="description_dynamic_info_window_adapter">Learn how to create a dynamic custom InfoWindow</string>
     <string name="description_viewpager">Use SupportMapFragments in a ViewPager</string>
     <string name="description_runtime_style">Adopt the map style on the fly</string>
+    <string name="description_distance_style">Show POIs on a map with distance expression filter</string>
     <string name="description_gradient_line">Show a gradient line layer from a geojson source</string>
     <string name="description_data_driven_style">Use functions to change the map appearance</string>
     <string name="description_symbol_layer">Manipulate symbols at runtime</string>

MapboxGLAndroidSDKTestApp/src/main/res/values/titles.xml

@@ -32,6 +32,7 @@
     <string name="activity_minmax_zoom">Min/Max Zoom</string>
     <string name="activity_viewpager">ViewPager</string>
     <string name="activity_runtime_style">Runtime Style</string>
+    <string name="activity_distance_style">Distance Expression</string>
     <string name="activity_gradient_line">Gradient line layer</string>
     <string name="activity_data_driven_style">Data Driven Style</string>
     <string name="activity_circle_layer">Circle layer</string>