[android] - Add touch velocity effects on scale gesture.

platform/android/MapboxGLAndroidSDK/src/main/java/com/mapbox/mapboxsdk/maps/MapGestureDetector.java

@@ -3,12 +3,14 @@ package com.mapbox.mapboxsdk.maps;
 import android.content.Context;
 import android.graphics.PointF;
 import android.location.Location;
+import android.os.Handler;
 import android.support.annotation.Nullable;
 import android.support.v4.view.GestureDetectorCompat;
 import android.support.v4.view.ScaleGestureDetectorCompat;
 import android.view.InputDevice;
 import android.view.MotionEvent;
 import android.view.ScaleGestureDetector;
+import android.view.VelocityTracker;
 import android.view.ViewConfiguration;
 
 import com.almeros.android.multitouch.gesturedetectors.RotateGestureDetector;
@@ -59,6 +61,10 @@ final class MapGestureDetector {
   private boolean recentScaleGestureOccurred;
   private long scaleBeginTime;
 
+  private VelocityTracker velocityTracker = null;
+  private boolean wasZoomingIn = false;
+  private final Handler handler = new Handler();
+
   MapGestureDetector(Context context, Transform transform, Projection projection, UiSettings uiSettings,
                      TrackingSettings trackingSettings, AnnotationManager annotationManager,
                      CameraChangeDispatcher cameraChangeDispatcher) {
@@ -153,6 +159,12 @@ final class MapGestureDetector {
     // Handle two finger tap
     switch (event.getActionMasked()) {
       case MotionEvent.ACTION_DOWN:
+        if (velocityTracker == null) {
+          velocityTracker = VelocityTracker.obtain();
+        } else {
+          velocityTracker.clear();
+        }
+        velocityTracker.addMovement(event);
         // First pointer down, reset scaleGestureOccurred, used to avoid triggering a fling after a scale gesture #7666
         recentScaleGestureOccurred = false;
         transform.setGestureInProgress(true);
@@ -180,7 +192,8 @@ final class MapGestureDetector {
         boolean isTap = tapInterval <= ViewConfiguration.getTapTimeout();
         boolean inProgress = rotateGestureDetector.isInProgress()
           || scaleGestureDetector.isInProgress()
-          || shoveGestureDetector.isInProgress();
+          || shoveGestureDetector.isInProgress()
+          || scaleGestureOccurred;
 
         if (twoTap && isTap && !inProgress) {
           if (focalPoint != null) {
@@ -203,11 +216,23 @@ final class MapGestureDetector {
 
         twoTap = false;
         transform.setGestureInProgress(false);
+        if (velocityTracker != null) {
+          velocityTracker.recycle();
+        }
+        velocityTracker = null;
         break;
 
       case MotionEvent.ACTION_CANCEL:
         twoTap = false;
         transform.setGestureInProgress(false);
+        if (velocityTracker != null) {
+          velocityTracker.recycle();
+        }
+        velocityTracker = null;
+        break;
+      case MotionEvent.ACTION_MOVE:
+        velocityTracker.addMovement(event);
+        velocityTracker.computeCurrentVelocity(1000);
         break;
     }
 
@@ -450,10 +475,22 @@ final class MapGestureDetector {
     // Called when fingers leave screen
     @Override
     public void onScaleEnd(ScaleGestureDetector detector) {
-      scaleGestureOccurred = false;
-      scaleBeginTime = 0;
-      scaleFactor = 1.0f;
-      cameraChangeDispatcher.onCameraIdle();
+      double velocityXY = Math.abs(velocityTracker.getYVelocity()) + Math.abs(velocityTracker.getXVelocity());
+      if (velocityXY > MapboxConstants.VELOCITY_THRESHOLD_IGNORE_FLING) {
+        long animationTime = (long)(Math.log(velocityXY) * 66);
+        transform.zoom(wasZoomingIn, new PointF(detector.getFocusX(), detector.getFocusY()), animationTime);
+        handler.postDelayed(new Runnable() {
+          @Override
+          public void run() {
+            scaleGestureOccurred = false;
+          }
+        }, animationTime);
+      } else {
+        scaleGestureOccurred = false;
+        scaleBeginTime = 0;
+        scaleFactor = 1.0f;
+        cameraChangeDispatcher.onCameraIdle();
+      }
     }
 
     // Called each time a finger moves
@@ -500,6 +537,7 @@ final class MapGestureDetector {
 
       trackingSettings.resetTrackingModesIfRequired(!quickZoom, false, false);
       // Scale the map
+      wasZoomingIn = (Math.log(detector.getScaleFactor()) / Math.log(Math.PI / 2)) >= 0;
       if (focalPoint != null) {
         // arround user provided focal point
         transform.zoomBy(Math.log(detector.getScaleFactor()) / Math.log(Math.PI / 2), focalPoint.x, focalPoint.y);

platform/android/MapboxGLAndroidSDK/src/main/java/com/mapbox/mapboxsdk/maps/Transform.java

@@ -221,6 +221,17 @@ final class Transform implements MapView.OnMapChangedListener {
     }
   }
 
+  void zoom(boolean zoomIn, @NonNull PointF focalPoint,long duration) {
+    CameraPosition cameraPosition = invalidateCameraPosition();
+    if (cameraPosition != null) {
+      int newZoom = (int) Math.round(cameraPosition.zoom + (zoomIn ? 1 : -1));
+      setZoom(newZoom, focalPoint, duration);
+    } else {
+      // we are not transforming, notify about being idle
+      cameraChangeDispatcher.onCameraIdle();
+    }
+  }
+
   void setZoom(double zoom, @NonNull PointF focalPoint) {
     setZoom(zoom, focalPoint, 0);
   }