screenPositionToLngLat returns false if position has no LngLat

core/src/tangram.cpp

@@ -514,14 +514,15 @@ float getTilt() {
 
 }
 
-void screenPositionToLngLat(double _x, double _y, double* _lng, double* _lat) {
+bool screenPositionToLngLat(double _x, double _y, double* _lng, double* _lat) {
 
-    m_view->screenToGroundPlane(_x, _y);
+    double intersection = m_view->screenToGroundPlane(_x, _y);
     glm::dvec2 meters(_x + m_view->getPosition().x, _y + m_view->getPosition().y);
     glm::dvec2 lngLat = m_view->getMapProjection().MetersToLonLat(meters);
     *_lng = lngLat.x;
     *_lat = lngLat.y;
 
+    return (intersection >= 0);
 }
 
 bool lngLatToScreenPosition(double _lng, double _lat, double* _x, double* _y) {

core/src/tangram.h

@@ -86,13 +86,14 @@ void setTilt(float _radians, float _duration, EaseType _e = EaseType::quint);
 // Get the tilt angle of the view in radians; 0 corresponds to straight down
 float getTilt();
 
-// Given coordinates in screen space (x right, y down), set the output longitude
-// and latitude to the geographic location corresponding to that point
-void screenPositionToLngLat(double _x, double _y, double* _lng, double* _lat);
+// Given coordinates in screen space (x right, y down), set the output longitude and
+// latitude to the geographic location corresponding to that point; returns false if
+// no geographic position corresponds to the screen location, otherwise returns true
+bool screenPositionToLngLat(double _x, double _y, double* _lng, double* _lat);
 
 // Given longitude and latitude coordinates, set the output coordinates to the
-// corresponding point in screen space (x right, y down); returns true if the
-// point is visible on the screen, otherwise returns false
+// corresponding point in screen space (x right, y down); returns false if the
+// point is not visible on the screen, otherwise returns true
 bool lngLatToScreenPosition(double _lng, double _lat, double* _x, double* _y);
 
 // Set the ratio of hardware pixels to logical pixels (defaults to 1.0)