From a01bddca77a22222530f82b26932ffd3326a81b8 Mon Sep 17 00:00:00 2001
From: Fabian Guerra <fabian.guerra@mapbox.com>
Date: Thu, 17 Aug 2017 19:15:43 -0400
Subject: [PATCH] [ios] Fix visible coordinates when boundaries cross
 international dateline.

---
 platform/darwin/src/MGLGeometry_Private.h | 45 +++++++++++++++++++++++
 platform/ios/src/MGLMapView.mm            | 25 +++++++++++++
 2 files changed, 70 insertions(+)

diff --git a/platform/darwin/src/MGLGeometry_Private.h b/platform/darwin/src/MGLGeometry_Private.h
index 7ad8314a792..6656b2ebbce 100644
--- a/platform/darwin/src/MGLGeometry_Private.h
+++ b/platform/darwin/src/MGLGeometry_Private.h
@@ -123,3 +123,48 @@ NS_INLINE MGLRadianCoordinate2D MGLRadianCoordinateAtDistanceFacingDirection(MGL
                                                          cos(distance) - sin(coordinate.latitude) * sin(otherLatitude));
     return MGLRadianCoordinate2DMake(otherLatitude, otherLongitude);
 }
+
+/** Returns the coordinate at a given fraction between two coordinates.
+ 
+ @param origin Origin `CLLocationCoordinate2D`.
+ @param destination Destination `CLLocationCoordinate2D`.
+ @param fraction Fraction between coordinates (0 = origin, 0.5 = middle, 1 = destination).
+ 
+ @return A coordinate at given fraction. */
+// Ported from http://www.movable-type.co.uk/scripts/latlong.html
+NS_INLINE CLLocationCoordinate2D MGLCLCoordinateAtFraction(CLLocationCoordinate2D origin, CLLocationCoordinate2D destination, double fraction) {
+    double φ1 = MGLRadiansFromDegrees(origin.latitude);
+    double λ1 = MGLRadiansFromDegrees(origin.longitude);
+    
+    double φ2 = MGLRadiansFromDegrees(destination.latitude);
+    double λ2 = MGLRadiansFromDegrees(destination.longitude);
+    double sinφ1 = sin(φ1);
+    double cosφ1 = cos(φ1);
+    double sinλ1 = sin(λ1);
+    double cosλ1 = cos(λ1);
+    double sinφ2 = sin(φ2);
+    double cosφ2 = cos(φ2);
+    double sinλ2 = sin(λ2);
+    double cosλ2 = cos(λ2);
+    
+    // distance between points
+    double Δφ = φ2 - φ1;
+    double Δλ = λ2 - λ1;
+    double a = sin(Δφ/2) * sin(Δφ/2) + cos(φ1) * cos(φ2) * sin(Δλ/2) * sin(Δλ/2);
+    double δ = 2 * atan2(sqrt(a), sqrt(1-a));
+    
+    double A = sin((1-fraction)*δ) / sin(δ);
+    double B = sin(fraction*δ) / sin(δ);
+    
+    double x = A * cosφ1 * cosλ1 + B * cosφ2 * cosλ2;
+    double y = A * cosφ1 * sinλ1 + B * cosφ2 * sinλ2;
+    double z = A * sinφ1 + B * sinφ2;
+    
+    double φ3 = atan2(z, sqrt(x*x + y*y));
+    double λ3 = atan2(y, x);
+    
+    CLLocationDegrees latitude = MGLDegreesFromRadians(φ3);
+    CLLocationDegrees longitude = fmod(MGLDegreesFromRadians(λ3), 360 - 180);
+    
+    return CLLocationCoordinate2DMake(latitude, longitude);
+}
diff --git a/platform/ios/src/MGLMapView.mm b/platform/ios/src/MGLMapView.mm
index 715c32186d9..17d655f9507 100644
--- a/platform/ios/src/MGLMapView.mm
+++ b/platform/ios/src/MGLMapView.mm
@@ -2667,8 +2667,21 @@ - (void)_setVisibleCoordinates:(const CLLocationCoordinate2D *)coordinates count
     {
         latLngs.push_back({coordinates[i].latitude, coordinates[i].longitude});
     }
+    
+    BOOL boundariesCrossDateTime = NO;
+    if (count == 4 && coordinates[1].longitude > 0 && coordinates[3].longitude < 0) {
+        boundariesCrossDateTime = YES;
+        latLngs = [self normalizeCoordinatesForDateTimeChangeSW:coordinates[1] ne:coordinates[3]];
+        
+    }
 
     mbgl::CameraOptions cameraOptions = _mbglMap->cameraForLatLngs(latLngs, padding);
+    
+    if (boundariesCrossDateTime) {
+        CLLocationCoordinate2D centerCoordinate = MGLCLCoordinateAtFraction(coordinates[1], coordinates[3], 0.5);
+        cameraOptions.center = MGLLatLngFromLocationCoordinate2D(centerCoordinate);
+    }
+    
     if (direction >= 0)
     {
         cameraOptions.angle = MGLRadiansFromDegrees(-direction);
@@ -2707,6 +2720,18 @@ - (void)_setVisibleCoordinates:(const CLLocationCoordinate2D *)coordinates count
     [self didChangeValueForKey:@"visibleCoordinateBounds"];
 }
 
+- (std::vector<mbgl::LatLng>)normalizeCoordinatesForDateTimeChangeSW:(CLLocationCoordinate2D)sw ne:(CLLocationCoordinate2D)ne
+{
+    CLLocationDegrees delta = (180 - fabs(sw.longitude)) + (180 - fabs(ne.longitude));
+    CLLocationCoordinate2D swap = sw;
+    sw = CLLocationCoordinate2DMake(ne.latitude, sw.longitude - delta);
+    ne = swap;
+    
+    std::vector<mbgl::LatLng> latLngs = { {ne.latitude, sw.longitude}, {sw.latitude, sw.longitude}, {sw.latitude, ne.longitude}, {ne.latitude, ne.longitude} };
+    
+    return latLngs;
+}
+
 + (NS_SET_OF(NSString *) *)keyPathsForValuesAffectingDirection
 {
     return [NSSet setWithObject:@"camera"];