Added BeginPopupContextItem() comment (#439)

imgui.cpp

@@ -3207,7 +3207,7 @@ void ImGui::CloseCurrentPopup()
     ClosePopupToLevel(popup_idx);
 }
 
-static void ClearSetNextWindowData()
+static inline void ClearSetNextWindowData()
 {
     ImGuiState& g = *GImGui;
     g.SetNextWindowPosCond = g.SetNextWindowSizeCond = g.SetNextWindowContentSizeCond = g.SetNextWindowCollapsedCond = g.SetNextWindowFocus = 0;
@@ -3282,11 +3282,16 @@ void ImGui::EndPopup()
         ImGui::PopStyleVar();
 }
 
-// FIXME: Allow to reopen existing, would need to a/ read DC.LastItemHoveredRect instead of DC.LastItemHoveredAndUsable and b/ add parameter to API (more tricky)
+// This is a helper to handle the most simple case of associating one named popup to one given widget.
+// 1. If you have many possible popups (for different "instances" of a same widget, or for wholly different widgets), you may be better off handling 
+//    this yourself so you can store data relative to the widget that opened the popup instead of choosing different popup identifiers.
+// 2. If you want right-clicking on the same item to reopen the popup at new location, use the same code replacing IsItemHovered() with IsItemHoveredRect().
+//    Because: hovering an item in a window below the popup won't normally trigger is hovering behavior/coloring. The pattern of ignoring the fact that 
+//    the item isn't interactable (because it is blocked by the active popup) may useful in some situation when e.g. large canvas as one item, content of menu
+//    driven by click position.
 bool ImGui::BeginPopupContextItem(const char* str_id, int mouse_button)
 {
-    ImGuiWindow* window = GetCurrentWindowRead();
-    if (window->DC.LastItemHoveredAndUsable && ImGui::IsMouseClicked(mouse_button))
+    if (ImGui::IsItemHovered() && ImGui::IsMouseClicked(mouse_button))
         ImGui::OpenPopupEx(str_id, false);
     return ImGui::BeginPopup(str_id);
 }

imgui.h

@@ -352,9 +352,9 @@ namespace ImGui
     IMGUI_API void          OpenPopup(const char* str_id);                                      // mark popup as open. popups are closed when user click outside, or activate a pressable item, or CloseCurrentPopup() is called within a BeginPopup()/EndPopup() block. popup identifiers are relative to the current ID-stack (so OpenPopup and BeginPopup needs to be at the same level). 
     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          BeginPopupModal(const char* name, bool* p_opened = NULL, ImGuiWindowFlags extra_flags = 0);             // modal dialog (can't close them by clicking outside)
-    IMGUI_API bool          BeginPopupContextItem(const char* str_id, int mouse_button = 1);                                        // helper to open and begin popup when clicked on last item
-    IMGUI_API bool          BeginPopupContextWindow(bool also_over_items = true, const char* str_id = NULL, int mouse_button = 1);  // helper to open and begin popup when clicked on current window
-    IMGUI_API bool          BeginPopupContextVoid(const char* str_id = NULL, int mouse_button = 1);                                 // helper to open and begin popup when clicked in void (no window)
+    IMGUI_API bool          BeginPopupContextItem(const char* str_id, int mouse_button = 1);                                        // helper to open and begin popup when clicked on last item. read comments in .cpp!
+    IMGUI_API bool          BeginPopupContextWindow(bool also_over_items = true, const char* str_id = NULL, int mouse_button = 1);  // helper to open and begin popup when clicked on current window.
+    IMGUI_API bool          BeginPopupContextVoid(const char* str_id = NULL, int mouse_button = 1);                                 // helper to open and begin 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.
 
@@ -368,7 +368,7 @@ namespace ImGui
 
     // Utilities
     IMGUI_API bool          IsItemHovered();                                                    // was the last item hovered by mouse?
-    IMGUI_API bool          IsItemHoveredRect();                                                // was the last item hovered by mouse? even if another item is active while we are hovering this
+    IMGUI_API bool          IsItemHoveredRect();                                                // was the last item hovered by mouse? even if another item is active or window is blocked by popup while we are hovering this
     IMGUI_API bool          IsItemActive();                                                     // was the last item active? (e.g. button being held, text field being edited- items that don't interact will always return false)
     IMGUI_API bool          IsItemVisible();                                                    // was the last item visible? (aka not out of sight due to clipping/scrolling.)
     IMGUI_API bool          IsAnyItemHovered();