Internals: Update ->RootWindow and other links before applying the SetNextWindowXXX stuff. This is so FocusWindow() can always assume that ->RootWindow != NULL.

imgui.cpp

@@ -5402,6 +5402,10 @@ bool ImGui::Begin(const char* name, bool* p_open, ImGuiWindowFlags flags)
     if (window_just_appearing_after_hidden_for_resize && !(flags & ImGuiWindowFlags_ChildWindow))
         window->NavLastIds[0] = 0;
 
+    // Update ->RootWindow and others pointers (before any possible call to FocusWindow)
+    if (first_begin_of_the_frame)
+        UpdateWindowParentAndRootLinks(window, flags, parent_window);
+
     // Process SetNextWindow***() calls
     bool window_pos_set_by_api = false;
     bool window_size_x_set_by_api = false, window_size_y_set_by_api = false;
@@ -5443,8 +5447,6 @@ bool ImGui::Begin(const char* name, bool* p_open, ImGuiWindowFlags flags)
     {
         // Initialize
         const bool window_is_child_tooltip = (flags & ImGuiWindowFlags_ChildWindow) && (flags & ImGuiWindowFlags_Tooltip); // FIXME-WIP: Undocumented behavior of Child+Tooltip for pinned tooltip (#1345)
-        UpdateWindowParentAndRootLinks(window, flags, parent_window);
-
         window->Active = true;
         window->HasCloseButton = (p_open != NULL);
         window->ClipRect = ImVec4(-FLT_MAX,-FLT_MAX,+FLT_MAX,+FLT_MAX);
@@ -6037,8 +6039,8 @@ void ImGui::FocusWindow(ImGuiWindow* window)
         return;
 
     // Move the root window to the top of the pile
-    if (window->RootWindow)
-        window = window->RootWindow;
+    IM_ASSERT(window->RootWindow != NULL);
+    window = window->RootWindow;
 
     // Steal focus on active widgets
     if (window->Flags & ImGuiWindowFlags_Popup) // FIXME: This statement should be unnecessary. Need further testing before removing it..
@@ -7823,7 +7825,7 @@ ImVec2 ImGui::FindBestWindowPosForPopup(ImGuiWindow* window)
 // [SECTION] KEYBOARD/GAMEPAD NAVIGATION
 //-----------------------------------------------------------------------------
 
-// FIXME-NAV: The existance of SetNavID vs SetNavIDWithRectRel vs SetFocusID is incredibly messy and confusing,
+// FIXME-NAV: The existence of SetNavID vs SetNavIDWithRectRel vs SetFocusID is incredibly messy and confusing,
 // and needs some explanation or serious refactoring.
 void ImGui::SetNavID(ImGuiID id, int nav_layer, ImGuiID focus_scope_id)
 {
@@ -8295,7 +8297,8 @@ static void ImGui::NavUpdate()
     if (g.NavScoringCount > 0) IMGUI_DEBUG_LOG("NavScoringCount %d for '%s' layer %d (Init:%d, Move:%d)\n", g.FrameCount, g.NavScoringCount, g.NavWindow ? g.NavWindow->Name : "NULL", g.NavLayer, g.NavInitRequest || g.NavInitResultId != 0, g.NavMoveRequest);
 #endif
 
-    // Set input source as Gamepad when buttons are pressed before we map Keyboard (some features differs when used with Gamepad vs Keyboard)
+    // Set input source as Gamepad when buttons are pressed (as some features differs when used with Gamepad vs Keyboard)
+    // (do it before we map Keyboard input!)
     bool nav_keyboard_active = (g.IO.ConfigFlags & ImGuiConfigFlags_NavEnableKeyboard) != 0;
     bool nav_gamepad_active = (g.IO.ConfigFlags & ImGuiConfigFlags_NavEnableGamepad) != 0 && (g.IO.BackendFlags & ImGuiBackendFlags_HasGamepad) != 0;
     if (nav_gamepad_active)