1 files changed, 11 insertions, 0 deletions
diff --git a/include/mbgl/map/backend.hpp b/include/mbgl/map/backend.hpp
index cd756abe43..876c19261b 100644
--- a/include/mbgl/map/backend.hpp
+++ b/include/mbgl/map/backend.hpp
@@ -3,11 +3,13 @@
 #include <mbgl/map/map_observer.hpp>
 
 #include <memory>
+#include <mutex>
 
 namespace mbgl {
 
 namespace gl {
 class Context;
+using ProcAddress = void (*)();
 } // namespace gl
 
 class BackendScope;
@@ -25,6 +27,11 @@ public:
     virtual void invalidate() = 0;
 
 protected:
+    // Called with the name of an OpenGL extension that should be loaded. Backend implementations
+    // must call the API-specific version that obtains the function pointer for this function,
+    // or a null pointer if unsupported/unavailable.
+    virtual gl::ProcAddress initializeExtension(const char*) = 0;
+
     // Called when the backend's GL context needs to be made active or inactive. These are called,
     // as a matched pair, in four situations:
     //
@@ -38,8 +45,12 @@ protected:
     virtual void activate() = 0;
     virtual void deactivate() = 0;
 
+protected:
     std::unique_ptr<gl::Context> context;
 
+private:
+    std::once_flag initialized;
+
     friend class BackendScope;
 };