[core] Ensure that a BackendScope exists when doing GL calls

1 files changed, 14 insertions, 1 deletions

diff --git a/include/mbgl/map/backend_scope.hpp b/include/mbgl/map/backend_scope.hpp
index 5a207e6ac4..4985cd197f 100644
--- a/include/mbgl/map/backend_scope.hpp
+++ b/include/mbgl/map/backend_scope.hpp
@@ -6,13 +6,26 @@ class Backend;
 
 class BackendScope {
 public:
-    BackendScope(Backend&);
+    // There are two types of scopes: Creating an "Implicit" scope tells Mapbox GL that the
+    // supporting windowing system has already activated the GL Backend and that no further actions
+    // are required. Creating an "Explicit" scope actually enables the GL Backend, and disables it
+    // when the BackendScope is destroyed.
+    enum class ScopeType : bool {
+        Implicit,
+        Explicit,
+    };
+
+    BackendScope(Backend&, ScopeType = ScopeType::Explicit);
     ~BackendScope();
 
+    // Returns true when there is currently a BackendScope active in this thread.
+    static bool exists();
+
 private:
     BackendScope* priorScope;
     BackendScope* nextScope;
     Backend& backend;
+    const ScopeType scopeType;
 };
 
 } // namespace mbgl