Adjustable map deceleration rate (#5504)

* [ios] Adds the ability to customize map deceleration speed

* [ios] Made pinch, rotation deceleration adjustable too

Drift zooming and drift rotation also respect the deceleration rate. A side effect of this change is that drift zooming will come to a stop ever-so-slightly sooner now.

* [ios] Documented deceleration rates

Added documentation for deceleration rate constants. Also updated the changelog.

1 files changed, 20 insertions, 0 deletions

diff --git a/platform/ios/src/MGLMapView.h b/platform/ios/src/MGLMapView.h
index 3f649e45d2..de851bc1e5 100644
--- a/platform/ios/src/MGLMapView.h
+++ b/platform/ios/src/MGLMapView.h
@@ -21,6 +21,15 @@ NS_ASSUME_NONNULL_BEGIN
 @protocol MGLCalloutView;
 @protocol MGLFeature;
 
+/** The default deceleration rate for a map view. */
+extern const CGFloat MGLMapViewDecelerationRateNormal;
+
+/** A fast deceleration rate for a map view. */
+extern const CGFloat MGLMapViewDecelerationRateFast;
+
+/** Disables decleration in a map view. */
+extern const CGFloat MGLMapViewDecelerationRateImmediate;
+
 /** The vertical alignment of an annotation within a map view. */
 typedef NS_ENUM(NSUInteger, MGLAnnotationVerticalAlignment) {
     /** Aligns the annotation vertically in the center of the map view. */
@@ -404,6 +413,17 @@ IB_DESIGNABLE
  */
 @property(nonatomic, getter=isPitchEnabled) BOOL pitchEnabled;
 
+/**
+ A floating-point value that determines the rate of deceleration after the user
+ lifts their finger.
+
+ Your application can use the `MGLMapViewDecelerationRateNormal` and
+ `MGLMapViewDecelerationRateFast` constants as reference points for reasonable
+ deceleration rates. `MGLMapViewDecelerationRateImmediate` can be used to
+ disable deceleration entirely.
+ */
+@property(nonatomic) CGFloat decelerationRate;
+
 #pragma mark Manipulating the Viewpoint
 
 /**