Added BeginPopupContextVoid() helper for completeness (#126)

imgui.cpp

@@ -3185,13 +3185,21 @@ bool ImGui::BeginPopupContextItem(const char* str_id, int button)
 
 bool ImGui::BeginPopupContextWindow(bool in_empty_space_only, const char* str_id, int button)
 {
-    if (str_id == NULL) str_id = "window_context_menu";
+    if (!str_id) str_id = "window_context_menu";
     if (ImGui::IsMouseHoveringWindow() && ImGui::IsMouseClicked(button))
         if (!in_empty_space_only || !ImGui::IsAnyItemHovered())
             ImGui::OpenPopup(str_id);
     return ImGui::BeginPopup(str_id);
 }
 
+bool ImGui::BeginPopupContextVoid(const char* str_id, int button)
+{
+    if (!str_id) str_id = "void_context_menu";
+    if (!ImGui::IsMouseHoveringAnyWindow() && ImGui::IsMouseClicked(button))
+        ImGui::OpenPopup(str_id);
+    return ImGui::BeginPopup(str_id);
+}
+
 bool ImGui::BeginChild(const char* str_id, const ImVec2& size_arg, bool border, ImGuiWindowFlags extra_flags)
 {
     ImGuiState& g = *GImGui;

imgui.h

@@ -170,7 +170,8 @@ namespace ImGui
     IMGUI_API void          OpenPopup(const char* str_id);                                      // mark popup as open. popup identifiers are relative to the current ID-stack (so OpenPopup and BeginPopup needs to be at the same level). close childs popups if any. will close popup when user click outside, or activate a pressable item, or CloseCurrentPopup() is called within a BeginPopup()/EndPopup() block.
     IMGUI_API bool          BeginPopup(const char* str_id);                                     // return true if popup if opened and start outputting to it. only call EndPopup() if BeginPopup() returned true!
     IMGUI_API bool          BeginPopupContextItem(const char* str_id, int button = 1);          // open popup when clicked on last item
-    IMGUI_API bool          BeginPopupContextWindow(bool in_void_only = false, const char* str_id = "window_context_menu", int button = 1);  // open popup when clicked on current window
+    IMGUI_API bool          BeginPopupContextWindow(bool in_empty_space_only = false, const char* str_id = "window_context_menu", int button = 1);  // open popup when clicked on current window
+    IMGUI_API bool          BeginPopupContextVoid(const char* str_id = "void_context_menu", int button = 1);                                        // open popup when clicked in void (no window)
     IMGUI_API void          EndPopup();
     IMGUI_API void          CloseCurrentPopup();                                                // close the popup we have begin-ed into. clicking on a MenuItem or Selectable automatically close the current popup.