[core] Added Map::latLngBoundsForCamera

include/mbgl/map/camera.hpp

@@ -36,6 +36,19 @@ struct CameraOptions {
     optional<double> pitch;
 };
 
+constexpr bool operator==(const CameraOptions& a, const CameraOptions& b) {
+    return a.center == b.center
+        && a.padding == b.padding
+        && a.anchor == b.anchor
+        && a.zoom == b.zoom
+        && a.angle == b.angle
+        && a.pitch == b.pitch;
+}
+
+constexpr bool operator!=(const CameraOptions& a, const CameraOptions& b) {
+    return !(a == b);
+}
+
 /** Various options for describing a transition between viewpoints with
     animation. All fields are optional; the default values depend on how this
     struct is used. */

include/mbgl/map/map.hpp

@@ -107,6 +107,7 @@ public:
     void setLatLngZoom(const LatLng&, double zoom, optional<EdgeInsets>, const AnimationOptions& = {});
     CameraOptions cameraForLatLngBounds(const LatLngBounds&, optional<EdgeInsets>) const;
     CameraOptions cameraForLatLngs(const std::vector<LatLng>&, optional<EdgeInsets>) const;
+    LatLngBounds latLngBoundsForCamera(const CameraOptions&) const;
     void resetZoom();
     void setMinZoom(const double minZoom);
     double getMinZoom() const;

include/mbgl/util/geo.hpp

@@ -218,4 +218,12 @@ public:
     ScreenCoordinate getCenter(uint16_t width, uint16_t height) const;
 };
 
+constexpr bool operator==(const EdgeInsets& a, const EdgeInsets& b) {
+    return a.top == b.top && a.left == b.left && a.bottom == b.bottom && a.right == b.right;
+}
+
+constexpr bool operator!=(const EdgeInsets& a, const EdgeInsets& b) {
+    return !(a == b);
+}
+
 } // namespace mbgl

src/mbgl/map/map.cpp

@@ -644,6 +644,17 @@ CameraOptions Map::cameraForLatLngs(const std::vector<LatLng>& latLngs, optional
     return options;
 }
 
+LatLngBounds Map::latLngBoundsForCamera(const CameraOptions& camera) const {
+    Transform shallow { impl->transform.getState() };
+    Size size = shallow.getState().getSize();
+
+    shallow.jumpTo(camera);
+    return LatLngBounds::hull(
+        shallow.screenCoordinateToLatLng({}),
+        shallow.screenCoordinateToLatLng({ double(size.width), double(size.height) })
+    );
+}
+
 void Map::resetZoom() {
     impl->cameraMutated = true;
     setZoom(0);

src/mbgl/map/transform.hpp

@@ -22,6 +22,8 @@ public:
               ConstrainMode = ConstrainMode::HeightOnly,
               ViewportMode = ViewportMode::Default);
 
+    Transform(const TransformState &state_) : observer(MapObserver::nullObserver()), state(state_) {}
+
     // Map view
     bool resize(Size size);
 

test/map/map.test.cpp

@@ -69,6 +69,28 @@ TEST(Map, LatLngBehavior) {
     ASSERT_DOUBLE_EQ(latLng1.longitude, latLng2.longitude);
 }
 
+TEST(Map, CameraToLatLngBounds) {
+    MapTest test;
+    Map map(test.backend, test.view.getSize(), 1, test.fileSource, test.threadPool, MapMode::Still);
+
+    map.setLatLngZoom({ 45, 90 }, 16);
+
+    LatLngBounds bounds = LatLngBounds::hull(
+            map.latLngForPixel({}),
+            map.latLngForPixel({ double(map.getSize().width), double(map.getSize().height) }));
+
+    CameraOptions camera = map.getCameraOptions({});
+
+    ASSERT_EQ(bounds, map.latLngBoundsForCamera(camera));
+
+    CameraOptions virtualCamera = map.cameraForLatLngBounds(bounds, {});
+    ASSERT_NEAR(*camera.zoom, *virtualCamera.zoom, 1e-7);
+    ASSERT_NEAR(*camera.angle, *virtualCamera.angle, 1e-10);
+    ASSERT_NEAR(*camera.pitch, *virtualCamera.pitch, 1e-10);
+    ASSERT_NEAR(camera.center->latitude, virtualCamera.center->latitude, 1e-10);
+    ASSERT_NEAR(camera.center->longitude, virtualCamera.center->longitude, 1e-10);
+}
+
 TEST(Map, Offline) {
     MapTest test;
     DefaultFileSource fileSource(":memory:", ".");