Internals: Allow ItemHoverable() to be used with id==0 to facilitate high-level read-only hover test in widget code.

imgui.cpp

@@ -3172,17 +3172,22 @@ bool ImGui::ItemHoverable(const ImRect& bb, ImGuiID id)
     if (window->DC.ItemFlags & ImGuiItemFlags_Disabled)
         return false;
 
-    SetHoveredID(id);
-
-    // [DEBUG] Item Picker tool!
-    // We perform the check here because SetHoveredID() is not frequently called (1~ time a frame), making
-    // the cost of this tool near-zero. We can get slightly better call-stack and support picking non-hovered
-    // items if we perform the test in ItemAdd(), but that would incur a small runtime cost.
-    // #define IMGUI_DEBUG_TOOL_ITEM_PICKER_EX in imconfig.h if you want this check to also be performed in ItemAdd().
-    if (g.DebugItemPickerActive && g.HoveredIdPreviousFrame == id)
-        GetForegroundDrawList()->AddRect(bb.Min, bb.Max, IM_COL32(255, 255, 0, 255));
-    if (g.DebugItemPickerBreakId == id)
-        IM_DEBUG_BREAK();
+    // We exceptionally allow this function to be called with id==0 to allow using it for easy high-level
+    // hover test in widgets code. We could also decide to split this function is two.
+    if (id != 0)
+    {
+        SetHoveredID(id);
+
+        // [DEBUG] Item Picker tool!
+        // We perform the check here because SetHoveredID() is not frequently called (1~ time a frame), making
+        // the cost of this tool near-zero. We can get slightly better call-stack and support picking non-hovered
+        // items if we perform the test in ItemAdd(), but that would incur a small runtime cost.
+        // #define IMGUI_DEBUG_TOOL_ITEM_PICKER_EX in imconfig.h if you want this check to also be performed in ItemAdd().
+        if (g.DebugItemPickerActive && g.HoveredIdPreviousFrame == id)
+            GetForegroundDrawList()->AddRect(bb.Min, bb.Max, IM_COL32(255, 255, 0, 255));
+        if (g.DebugItemPickerBreakId == id)
+            IM_DEBUG_BREAK();
+    }
 
     return true;
 }