[ios] Don't use negative content insets

When a map view was smaller than the entire viewport, negative content insets would be applied. Negative content insets would only be valid if the map view extended outside of its frame, which cannot happen.

Fixes #4440.

platform/ios/CHANGELOG.md

@@ -21,6 +21,7 @@ Mapbox welcomes participation and contributions from everyone.  If you’d like
 - The Improve This Map tool now uses the same zoom level that is currently being shown in the map view. ([#4068](https://github.com/mapbox/mapbox-gl-native/pull/4068))
 - Fixed a formatting issue in the documentation for `MGLCoordinateBoundsIsEmpty()`. ([#3958](https://github.com/mapbox/mapbox-gl-native/pull/3958))
 - Fixed issues with configuration and documentation that caused problems when installing apps built with the static binary to devices. This change also fixed App Store submission problems when uploading an app built with the static binary. ([#4455](https://github.com/mapbox/mapbox-gl-native/pull/4455))
+- Fixed an issue where the map view’s center would always be calculated as if the view occupied the entire screen. ([#4504](https://github.com/mapbox/mapbox-gl-native/issues/4504))
 
 ## 3.1.2
 

platform/ios/src/MGLMapView.mm

@@ -814,6 +814,11 @@ - (void)adjustContentInset
                                       - viewController.bottomLayoutGuide.length);
     contentInset.bottom = (CGRectGetMaxY(self.bounds)
                            - [self convertPoint:bottomPoint fromView:viewController.view].y);
+
+    // Negative insets are invalid, replace with 0.
+    contentInset.top = fmaxf(contentInset.top, 0);
+    contentInset.bottom = fmaxf(contentInset.bottom, 0);
+
     self.contentInset = contentInset;
 }
 

platform/ios/test/MGLTViewController.h

@@ -3,6 +3,7 @@
 @interface MGLTViewController : UIViewController
 
 - (void)insetMapView;
+- (void)tinyMapView;
 - (void)resetMapView;
 
 @end

platform/ios/test/MGLTViewController.m

@@ -21,6 +21,11 @@ - (void)insetMapView
     _mapView.frame = CGRectInset(_mapView.frame, 50, 50);
 }
 
+- (void)tinyMapView
+{
+    _mapView.frame = CGRectMake(20, self.topLayoutGuide.length, self.view.frame.size.width / 2, self.view.frame.size.height / 2);
+}
+
 - (void)resetMapView
 {
     _mapView.frame = self.view.bounds;

platform/ios/test/MapViewTests.m

@@ -424,6 +424,29 @@ - (void)testInsetMapView {
                   @"compass should lie inside shrunken map view");
 }
 
+- (void)testContentInsetsWithTinyMapView {
+    [tester.viewController tinyMapView];
+    [self keyValueObservingExpectationForObject:tester.mapView keyPath:@"contentInset" handler:^BOOL(id observedObject, NSDictionary *change) {
+        XCTAssertEqual(tester.mapView.contentInset.top,
+                       0,
+                       @"map should not have top content inset");
+        XCTAssertEqual(tester.mapView.contentInset.bottom,
+                       0,
+                       @"map should not have bottom content inset");
+        return YES;
+    }];
+    [self waitForExpectationsWithTimeout:5.0 handler:nil];
+
+    tester.mapView.frame = CGRectMake(0, 0, tester.mapView.frame.size.width, tester.mapView.frame.size.height);
+    [self keyValueObservingExpectationForObject:tester.mapView keyPath:@"contentInset" handler:^BOOL(id observedObject, NSDictionary *change) {
+        XCTAssertEqual(tester.mapView.contentInset.top,
+                       tester.viewController.topLayoutGuide.length,
+                       @"map should have top content inset equal to the top layout guide");
+        return YES;
+    }];
+    [self waitForExpectationsWithTimeout:5.0 handler:nil];
+}
+
 - (void)testDelegateRegionWillChange {
     __block NSUInteger unanimatedCount;
     __block NSUInteger animatedCount;