Docking: Dockspace() never draws a background. (#3924)

imgui.cpp

@@ -14747,22 +14747,19 @@ void ImGui::DockSpace(ImGuiID id, const ImVec2& size_arg, ImGuiDockNodeFlags fla
     SetNextWindowSize(node->Size);
     g.NextWindowData.PosUndock = false;
 
-    // FIXME-DOCK Why do we need a child window to host a dockspace, could we host it in the existing window?
+    // FIXME-DOCK: Why do we need a child window to host a dockspace, could we host it in the existing window?
+    // FIXME-DOCK: What is the reason for not simply calling BeginChild()? (OK to have a reason but should be commented)
     ImGuiWindowFlags window_flags = ImGuiWindowFlags_ChildWindow | ImGuiWindowFlags_DockNodeHost;
     window_flags |= ImGuiWindowFlags_NoSavedSettings | ImGuiWindowFlags_NoResize | ImGuiWindowFlags_NoCollapse | ImGuiWindowFlags_NoTitleBar;
     window_flags |= ImGuiWindowFlags_NoScrollbar | ImGuiWindowFlags_NoScrollWithMouse;
+    window_flags |= ImGuiWindowFlags_NoBackground;
 
     char title[256];
     ImFormatString(title, IM_ARRAYSIZE(title), "%s/DockSpace_%08X", window->Name, id);
 
-    // FIXME-DOCK: What is the reason for not simply calling BeginChild()?
-    if (node->Windows.Size > 0 || node->IsSplitNode())
-        PushStyleColor(ImGuiCol_ChildBg, IM_COL32(0, 0, 0, 0));
     PushStyleVar(ImGuiStyleVar_ChildBorderSize, 0.0f);
     Begin(title, NULL, window_flags);
     PopStyleVar();
-    if (node->Windows.Size > 0 || node->IsSplitNode())
-        PopStyleColor();
 
     ImGuiWindow* host_window = g.CurrentWindow;
     host_window->DockNodeAsHost = node;