Docking: Fixed single-frame node pos/size inconsistencies when window stop or start being submitted.

Fix 718e15c7d while preserving its intended property. Tested by "docking_window_appearing_layout". (#2109)

docs/CHANGELOG.txt

@@ -159,6 +159,7 @@ Docking+Viewports Branch:
 - Docking: Fixed a bug undocking windows docked into a non-visible or _KeepAliveOnly dockspace
   when unrelated windows submitted before the dockspace have dynamic visibility. (#4757)
 - Docking: Fixed incorrectly rounded tab bars for dock node that are not at the top of their dock tree.
+- Docking: Fixed single-frame node pos/size inconsistencies when window stop or start being submitted.
 - Viewports: Made it possible to explicitly assign ImGuiWindowClass::ParentViewportId to 0 in order
   to ensure a window is not parented. Previously this would use the global default (which might be 0,
   but not always as it would depend on io.ConfigViewportsNoDefaultParent). (#3152, #2871)

imgui.cpp

@@ -12908,7 +12908,7 @@ namespace ImGui
     // ImGuiDockNode tree manipulations
     static void             DockNodeTreeSplit(ImGuiContext* ctx, ImGuiDockNode* parent_node, ImGuiAxis split_axis, int split_first_child, float split_ratio, ImGuiDockNode* new_node);
     static void             DockNodeTreeMerge(ImGuiContext* ctx, ImGuiDockNode* parent_node, ImGuiDockNode* merge_lead_child);
-    static void             DockNodeTreeUpdatePosSize(ImGuiDockNode* node, ImVec2 pos, ImVec2 size, bool only_write_to_marked_nodes = false);
+    static void             DockNodeTreeUpdatePosSize(ImGuiDockNode* node, ImVec2 pos, ImVec2 size, ImGuiDockNode* only_write_to_single_node = NULL);
     static void             DockNodeTreeUpdateSplitter(ImGuiDockNode* node);
     static ImGuiDockNode*   DockNodeTreeFindVisibleNodeByPos(ImGuiDockNode* node, ImVec2 pos);
     static ImGuiDockNode*   DockNodeTreeFindFallbackLeafNode(ImGuiDockNode* node);
@@ -13604,7 +13604,6 @@ ImGuiDockNode::ImGuiDockNode(ImGuiID id)
     IsVisible = true;
     IsFocused = HasCloseButton = HasWindowMenuButton = HasCentralNodeChild = false;
     WantCloseAll = WantLockSizeOnce = WantMouseMove = WantHiddenTabBarUpdate = WantHiddenTabBarToggle = false;
-    MarkedForPosSizeWrite = false;
 }
 
 ImGuiDockNode::~ImGuiDockNode()
@@ -14045,7 +14044,6 @@ static void ImGui::DockNodeUpdate(ImGuiDockNode* node)
     ImGuiContext& g = *GImGui;
     IM_ASSERT(node->LastFrameActive != g.FrameCount);
     node->LastFrameAlive = g.FrameCount;
-    node->MarkedForPosSizeWrite = false;
 
     node->CentralNode = node->OnlyNodeWithWindows = NULL;
     if (node->IsRootNode())
@@ -15153,11 +15151,11 @@ void ImGui::DockNodeTreeMerge(ImGuiContext* ctx, ImGuiDockNode* parent_node, ImG
 
 // Update Pos/Size for a node hierarchy (don't affect child Windows yet)
 // (Depth-first, Pre-Order)
-void ImGui::DockNodeTreeUpdatePosSize(ImGuiDockNode* node, ImVec2 pos, ImVec2 size, bool only_write_to_marked_nodes)
+void ImGui::DockNodeTreeUpdatePosSize(ImGuiDockNode* node, ImVec2 pos, ImVec2 size, ImGuiDockNode* only_write_to_single_node)
 {
     // During the regular dock node update we write to all nodes.
-    // 'only_write_to_marked_nodes' is only set when turning a node visible mid-frame and we need its size right-away.
-    const bool write_to_node = (only_write_to_marked_nodes == false) || (node->MarkedForPosSizeWrite);
+    // 'only_write_to_single_node' is only set when turning a node visible mid-frame and we need its size right-away.
+    const bool write_to_node = only_write_to_single_node == NULL || only_write_to_single_node == node;
     if (write_to_node)
     {
         node->Pos = pos;
@@ -15171,15 +15169,21 @@ void ImGui::DockNodeTreeUpdatePosSize(ImGuiDockNode* node, ImVec2 pos, ImVec2 si
     ImGuiDockNode* child_1 = node->ChildNodes[1];
     ImVec2 child_0_pos = pos, child_1_pos = pos;
     ImVec2 child_0_size = size, child_1_size = size;
-    if (child_0->IsVisible && child_1->IsVisible)
+
+    const bool child_0_is_toward_single_node = (only_write_to_single_node != NULL && DockNodeIsInHierarchyOf(only_write_to_single_node, child_0));
+    const bool child_1_is_toward_single_node = (only_write_to_single_node != NULL && DockNodeIsInHierarchyOf(only_write_to_single_node, child_1));
+    const bool child_0_is_or_will_be_visible = child_0->IsVisible || child_0_is_toward_single_node;
+    const bool child_1_is_or_will_be_visible = child_1->IsVisible || child_1_is_toward_single_node;
+
+    if (child_0_is_or_will_be_visible && child_1_is_or_will_be_visible)
     {
+        ImGuiContext& g = *GImGui;
         const float spacing = DOCKING_SPLITTER_SIZE;
         const ImGuiAxis axis = (ImGuiAxis)node->SplitAxis;
         const float size_avail = ImMax(size[axis] - spacing, 0.0f);
 
         // Size allocation policy
         // 1) The first 0..WindowMinSize[axis]*2 are allocated evenly to both windows.
-        ImGuiContext& g = *GImGui;
         const float size_min_each = ImFloor(ImMin(size_avail, g.Style.WindowMinSize[axis] * 2.0f) * 0.5f);
 
         // FIXME: Blocks 2) and 3) are essentially doing nearly the same thing.
@@ -15230,11 +15234,15 @@ void ImGui::DockNodeTreeUpdatePosSize(ImGuiDockNode* node, ImVec2 pos, ImVec2 si
 
         child_1_pos[axis] += spacing + child_0_size[axis];
     }
+
+    if (only_write_to_single_node == NULL)
         child_0->WantLockSizeOnce = child_1->WantLockSizeOnce = false;
 
-    if (child_0->IsVisible)
+    const bool child_0_recurse = only_write_to_single_node ? child_0_is_toward_single_node : child_0->IsVisible;
+    const bool child_1_recurse = only_write_to_single_node ? child_1_is_toward_single_node : child_1->IsVisible;
+    if (child_0_recurse)
         DockNodeTreeUpdatePosSize(child_0, child_0_pos, child_0_size);
-    if (child_1->IsVisible)
+    if (child_1_recurse)
         DockNodeTreeUpdatePosSize(child_1, child_1_pos, child_1_size);
 }
 
@@ -16048,16 +16056,11 @@ static ImGuiDockNode* ImGui::DockContextBindNodeToWindow(ImGuiContext* ctx, ImGu
     if (!node->IsVisible)
     {
         ImGuiDockNode* ancestor_node = node;
-        while (!ancestor_node->IsVisible)
-        {
-            ancestor_node->IsVisible = true;
-            ancestor_node->MarkedForPosSizeWrite = true;
-            if (ancestor_node->ParentNode)
+        while (!ancestor_node->IsVisible && ancestor_node->ParentNode)
             ancestor_node = ancestor_node->ParentNode;
-        }
         IM_ASSERT(ancestor_node->Size.x > 0.0f && ancestor_node->Size.y > 0.0f);
         DockNodeUpdateHasCentralNodeChild(DockNodeGetRootNode(ancestor_node));
-        DockNodeTreeUpdatePosSize(ancestor_node, ancestor_node->Pos, ancestor_node->Size, true);
+        DockNodeTreeUpdatePosSize(ancestor_node, ancestor_node->Pos, ancestor_node->Size, node);
     }
 
     // Add window to node

imgui_internal.h

@@ -1457,7 +1457,6 @@ struct IMGUI_API ImGuiDockNode
     bool                    WantMouseMove           :1; // After a node extraction we need to transition toward moving the newly created host window
     bool                    WantHiddenTabBarUpdate  :1;
     bool                    WantHiddenTabBarToggle  :1;
-    bool                    MarkedForPosSizeWrite   :1; // Update by DockNodeTreeUpdatePosSize() write-filtering
 
     ImGuiDockNode(ImGuiID id);
     ~ImGuiDockNode();
@@ -2837,6 +2836,7 @@ namespace ImGui
     IMGUI_API bool          DockNodeBeginAmendTabBar(ImGuiDockNode* node);
     IMGUI_API void          DockNodeEndAmendTabBar();
     inline ImGuiDockNode*   DockNodeGetRootNode(ImGuiDockNode* node)                 { while (node->ParentNode) node = node->ParentNode; return node; }
+    inline bool             DockNodeIsInHierarchyOf(ImGuiDockNode* node, ImGuiDockNode* parent) { while (node) { if (node == parent) return true; node = node->ParentNode; } return false; }
     inline int              DockNodeGetDepth(const ImGuiDockNode* node)              { int depth = 0; while (node->ParentNode) { node = node->ParentNode; depth++; } return depth; }
     inline ImGuiID          DockNodeGetWindowMenuButtonId(const ImGuiDockNode* node) { return ImHashStr("#COLLAPSE", 0, node->ID); }
     inline ImGuiDockNode*   GetWindowDockNode()                                      { ImGuiContext& g = *GImGui; return g.CurrentWindow->DockNode; }