Improve fling animation (#963)

Co-authored-by: Ovidiu Voda <ovi.voda@gmail.com>

platform/android/CHANGELOG.md

@@ -6,6 +6,8 @@ MapLibre welcomes participation and contributions from everyone. Please read [`C
 
 ### ✨ Features and improvements
 
+* Change to a more natural fling animation and allow setting `flingThreshold` and `flingAnimationBaseTime` in `UiSettings` ([#963](https://github.com/maplibre/maplibre-gl-native/pull/963))
+
 ### 🐞 Bug fixes
 
 ### ⛵ Dependencies

platform/android/MapboxGLAndroidSDK/src/cpp/native_map_view.cpp

@@ -329,7 +329,7 @@ void NativeMapView::moveBy(jni::JNIEnv&, jni::jdouble dx, jni::jdouble dy, jni::
     mbgl::AnimationOptions animationOptions;
     if (duration > 0) {
        animationOptions.duration.emplace(mbgl::Milliseconds(duration));
-       animationOptions.easing.emplace(mbgl::util::UnitBezier {0.25, 0.46, 0.45, 0.94});
+       animationOptions.easing.emplace(mbgl::util::UnitBezier {0.1, 0.4, 0.35, 1.0});
     }
     map->moveBy({dx, dy}, animationOptions);
 }

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

@@ -419,7 +419,7 @@ final class MapGestureDetector {
 
       // calculate velocity vector for xy dimensions, independent from screen size
       double velocityXY = Math.hypot(velocityX / screenDensity, velocityY / screenDensity);
-      if (velocityXY < MapboxConstants.VELOCITY_THRESHOLD_IGNORE_FLING) {
+      if (velocityXY < uiSettings.getFlingThreshold()) {
         // ignore short flings, these can occur when other gestures just have finished executing
         return false;
       }
@@ -427,11 +427,17 @@ final class MapGestureDetector {
       // tilt results in a bigger translation, limiting input for #5281
       double tilt = transform.getTilt();
       double tiltFactor = 1.5 + ((tilt != 0) ? (tilt / 10) : 0);
-      double offsetX = velocityX / tiltFactor / screenDensity;
-      double offsetY = velocityY / tiltFactor / screenDensity;
 
       // calculate animation time based on displacement
-      long animationTime = (long) (velocityXY / 7 / tiltFactor + MapboxConstants.ANIMATION_DURATION_FLING_BASE);
+      long animationTime = (long) (velocityXY / 7 / tiltFactor + uiSettings.getFlingAnimationBaseTime());
+
+      // screenDensity and influcentcetilt come in here via animationTime
+      // factor 1000 because speed is in pixels/s
+      // and the factor 0.28 was determined by testing: panning the map and releasing
+      //  should result in fling animation starting at same speed as the move before
+      double offsetX = velocityX * animationTime * 0.28 / 1000;
+      double offsetY = velocityY * animationTime * 0.28 / 1000;
+
       if (!uiSettings.isHorizontalScrollGesturesEnabled()) {
         // determine if angle of fling is valid for performing a vertical fling
         double angle = Math.abs(Math.toDegrees(Math.atan(offsetX / offsetY)));
@@ -1154,4 +1160,4 @@ final class MapGestureDetector {
     initializeGesturesManager(gesturesManager, setDefaultMutuallyExclusives);
     initializeGestureListeners(context, attachDefaultListeners);
   }
-}
+}

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

@@ -83,6 +83,9 @@ public final class UiSettings {
 
   private boolean deselectMarkersOnTap = true;
 
+  private long flingAnimationBaseTime = MapboxConstants.ANIMATION_DURATION_FLING_BASE;
+  private long flingThreshold = MapboxConstants.VELOCITY_THRESHOLD_IGNORE_FLING;
+
   @Nullable
   private PointF userProvidedFocalPoint;
 
@@ -316,6 +319,22 @@ public final class UiSettings {
       savedInstanceState.getInt(MapboxConstants.STATE_ATTRIBUTION_MARGIN_BOTTOM));
   }
 
+  public long getFlingAnimationBaseTime() {
+    return flingAnimationBaseTime;
+  }
+
+  public long getFlingThreshold() {
+    return flingThreshold;
+  }
+
+  public void setFlingAnimationBaseTime(long t) {
+    flingAnimationBaseTime = t;
+  }
+
+  public void setFlingThreshold(long t) {
+    flingThreshold = t;
+  }
+
   /**
    * <p>
    * Enables or disables the compass. The compass is an icon on the map that indicates the