[core] refactor program object creation

3 files changed, 49 insertions, 3 deletions

diff --git a/include/mbgl/gfx/backend.hpp b/include/mbgl/gfx/backend.hpp
new file mode 100644
index 0000000000..eed63dfcba
--- /dev/null
+++ b/include/mbgl/gfx/backend.hpp
@@ -0,0 +1,44 @@
+#pragma once
+
+#include <cstdint>
+#include <cstdlib>
+#include <memory>
+
+namespace mbgl {
+namespace gfx {
+
+class Backend {
+public:
+    enum class Type : uint8_t {
+        OpenGL,
+    };
+
+    static constexpr Type DefaultType = Type::OpenGL;
+
+    static void SetType(const Type value) {
+        if (Value(value) != value) {
+            abort(); // SetType must be called prior to any GetType calls.
+        }
+    }
+
+    static Type GetType() {
+        return Value(DefaultType);
+    }
+
+    template <typename T, typename... Args>
+    static std::unique_ptr<T> Create(Args... args) {
+        return Create<Type::OpenGL, T, Args...>(std::forward<Args>(args)...);
+    }
+
+private:
+    template <Type, typename T, typename... Args>
+    static std::unique_ptr<T> Create(Args...);
+
+    static Type Value(Type value) {
+        static const Type type = value;
+        return type;
+    }
+};
+
+} // namespace gfx
+} // namespace mbgl
diff --git a/include/mbgl/gfx/renderer_backend.hpp b/include/mbgl/gfx/renderer_backend.hpp
index 29f6b43a8f..aa76d7e502 100644
--- a/include/mbgl/gfx/renderer_backend.hpp
+++ b/include/mbgl/gfx/renderer_backend.hpp
@@ -30,6 +30,11 @@ public:
     // Returns the device's context.
     Context& getContext();
 
+    template <typename T>
+    T& getContext() {
+        return static_cast<T&>(getContext());
+    }
+
     bool contextIsShared() const {
         return contextMode == ContextMode::Shared;
     }
diff --git a/include/mbgl/gl/renderer_backend.hpp b/include/mbgl/gl/renderer_backend.hpp
index ba87e4ce4f..cfa28ddaeb 100644
--- a/include/mbgl/gl/renderer_backend.hpp
+++ b/include/mbgl/gl/renderer_backend.hpp
@@ -17,9 +17,6 @@ public:
     RendererBackend(gfx::ContextMode);
     ~RendererBackend() override;
 
-    // Returns the backend's context which manages OpenGL state.
-    Context& getGLContext();
-
     // Called prior to rendering to update the internally assumed OpenGL state.
     virtual void updateAssumedState() = 0;