1 files changed, 46 insertions, 0 deletions
diff --git a/platform/darwin/src/MGLGeometry.mm b/platform/darwin/src/MGLGeometry.mm
new file mode 100644
index 0000000000..70f00afd2f
--- /dev/null
+++ b/platform/darwin/src/MGLGeometry.mm
@@ -0,0 +1,46 @@
+#import "MGLGeometry_Private.h"
+
+#import <mbgl/util/projection.hpp>
+
+/** Vertical field of view, measured in degrees, for determining the altitude
+    of the viewpoint.
+    
+    TransformState::getProjMatrix() assumes a vertical field of view of
+    2 arctan ⅓ rad ≈ 36.9°, but MapKit uses a vertical field of view of 30°.
+    flyTo() assumes a field of view of 2 arctan ½ rad. */
+const CLLocationDegrees MGLAngularFieldOfView = 30;
+
+const MGLCoordinateSpan MGLCoordinateSpanZero = {0, 0};
+
+CGRect MGLExtendRect(CGRect rect, CGPoint point) {
+    if (point.x < rect.origin.x) {
+        rect.size.width += rect.origin.x - point.x;
+        rect.origin.x = point.x;
+    }
+    if (point.x > rect.origin.x + rect.size.width) {
+        rect.size.width += point.x - (rect.origin.x + rect.size.width);
+    }
+    if (point.y < rect.origin.y) {
+        rect.size.height += rect.origin.y - point.y;
+        rect.origin.y = point.y;
+    }
+    if (point.y > rect.origin.y + rect.size.height) {
+        rect.size.height += point.y - (rect.origin.y + rect.size.height);
+    }
+    return rect;
+}
+
+CLLocationDistance MGLAltitudeForZoomLevel(double zoomLevel, CGFloat pitch, CLLocationDegrees latitude, CGSize size) {
+    CLLocationDistance metersPerPixel = mbgl::Projection::getMetersPerPixelAtLatitude(latitude, zoomLevel);
+    CLLocationDistance metersTall = metersPerPixel * size.height;
+    CLLocationDistance altitude = metersTall / 2 / std::tan(MGLRadiansFromDegrees(MGLAngularFieldOfView) / 2.);
+    return altitude * std::sin(M_PI_2 - MGLRadiansFromDegrees(pitch)) / std::sin(M_PI_2);
+}
+
+double MGLZoomLevelForAltitude(CLLocationDistance altitude, CGFloat pitch, CLLocationDegrees latitude, CGSize size) {
+    CLLocationDistance eyeAltitude = altitude / std::sin(M_PI_2 - MGLRadiansFromDegrees(pitch)) * std::sin(M_PI_2);
+    CLLocationDistance metersTall = eyeAltitude * 2 * std::tan(MGLRadiansFromDegrees(MGLAngularFieldOfView) / 2.);
+    CLLocationDistance metersPerPixel = metersTall / size.height;
+    CGFloat mapPixelWidthAtZoom = std::cos(MGLRadiansFromDegrees(latitude)) * mbgl::util::M2PI * mbgl::util::EARTH_RADIUS_M / metersPerPixel;
+    return ::log2(mapPixelWidthAtZoom / mbgl::util::tileSize);
+}