Make use of extra keys in node editor optional thedmd#25

ImGuiKey_D and ImGuiKey_F are used in node editor only if they
are defined in ImGuiKey_ enum.

This commit can be removed when/if ocornut/imgui#2625
PR will be merged.

NodeEditor/Source/imgui_node_editor.cpp

@@ -16,6 +16,61 @@
 # include <algorithm>
 # include <sstream>
 # include <streambuf>
+# include <type_traits>
+
+// https://stackoverflow.com/a/8597498
+# define DECLARE_HAS_NESTED(Name, Member)                                          \
+                                                                                   \
+    template<class T>                                                              \
+    struct has_nested_ ## Name                                                     \
+    {                                                                              \
+        typedef char yes;                                                          \
+        typedef yes(&no)[2];                                                       \
+                                                                                   \
+        template<class U> static yes test(decltype(U::Member)*);                   \
+        template<class U> static no  test(...);                                    \
+                                                                                   \
+        static bool const value = sizeof(test<T>(0)) == sizeof(yes);               \
+    };
+
+
+namespace ax {
+namespace NodeEditor {
+namespace Detail {
+
+# define DECLARE_KEY_TESTER(Key)                                                                    \
+    DECLARE_HAS_NESTED(Key, Key)                                                                    \
+    struct KeyTester_ ## Key                                                                        \
+    {                                                                                               \
+        template <typename T>                                                                       \
+        static int Get(typename std::enable_if<has_nested_ ## Key<ImGuiKey_>::value, T>::type*)     \
+        {                                                                                           \
+            return ImGui::GetKeyIndex(T::Key);                                                      \
+        }                                                                                           \
+                                                                                                    \
+        template <typename T>                                                                       \
+        static int Get(typename std::enable_if<!has_nested_ ## Key<ImGuiKey_>::value, T>::type*)    \
+        {                                                                                           \
+            return -1;                                                                              \
+        }                                                                                           \
+    }
+
+DECLARE_KEY_TESTER(ImGuiKey_F);
+DECLARE_KEY_TESTER(ImGuiKey_D);
+
+static inline int GetKeyIndexForF()
+{
+    return KeyTester_ImGuiKey_F::Get<ImGuiKey_>(nullptr);
+}
+
+static inline int GetKeyIndexForD()
+{
+    return KeyTester_ImGuiKey_D::Get<ImGuiKey_>(nullptr);
+}
+
+} // namespace Detail
+} // namespace NodeEditor
+} // namespace ax
 
 
 //------------------------------------------------------------------------------
@@ -2791,7 +2846,7 @@ ed::EditorAction::AcceptResult ed::NavigateAction::Accept(const Control& control
 
     auto& io = ImGui::GetIO();
 
-    if (ImGui::IsWindowFocused() && ImGui::IsKeyPressed(ImGui::GetKeyIndex(ImGuiKey_F)) && Editor->AreShortcutsEnabled())
+    if (ImGui::IsWindowFocused() && ImGui::IsKeyPressed(GetKeyIndexForF()) && Editor->AreShortcutsEnabled())
     {
         const auto allowZoomIn = io.KeyShift;
 
@@ -3791,7 +3846,7 @@ ed::EditorAction::AcceptResult ed::ShortcutAction::Accept(const Control& control
         candidateAction = Copy;
     if (io.KeyCtrl && !io.KeyShift && !io.KeyAlt && ImGui::IsKeyPressed(ImGui::GetKeyIndex(ImGuiKey_V)))
         candidateAction = Paste;
-    if (io.KeyCtrl && !io.KeyShift && !io.KeyAlt && ImGui::IsKeyPressed(ImGui::GetKeyIndex(ImGuiKey_D)))
+    if (io.KeyCtrl && !io.KeyShift && !io.KeyAlt && ImGui::IsKeyPressed(GetKeyIndexForD()))
         candidateAction = Duplicate;
     if (!io.KeyCtrl && !io.KeyShift && !io.KeyAlt && ImGui::IsKeyPressed(ImGui::GetKeyIndex(ImGuiKey_Space)))
         candidateAction = CreateNode;