Docking: Fixed assert in DockContextProcessDock() preventing some uses of DockNodeBuilder api. (#2357, #2109)

imgui.cpp

@@ -10624,8 +10624,9 @@ void ImGui::DockContextProcessDock(ImGuiContext* ctx, ImGuiDockRequest* req)
     }
 
     // FIXME-DOCK: When we are trying to dock an existing single-window node into a loose window, transfer Node ID as well
+    // When processing an interactive split, usually LastFrameAlive will be < g.FrameCount. But DockBuilder operations can make it ==.
     if (target_node)
-        IM_ASSERT(target_node->LastFrameAlive < g.FrameCount);
+        IM_ASSERT(target_node->LastFrameAlive <= g.FrameCount);
     if (target_node && target_window && target_node == target_window->DockNodeAsHost)
         IM_ASSERT(target_node->Windows.Size > 0 || target_node->IsSplitNode() || target_node->IsCentralNode);
 
@@ -11975,7 +11976,7 @@ void ImGui::DockNodeTreeSplit(ImGuiContext* ctx, ImGuiDockNode* parent_node, ImG
     parent_node->VisibleWindow = NULL;
 
     float size_avail = (parent_node->Size[split_axis] - IMGUI_DOCK_SPLITTER_SIZE);
-    IM_ASSERT(size_avail > 0.0f);
+    IM_ASSERT(size_avail > 0.0f); // If you created a node manually with DockBuilderAddNode(), you need to also call DockBuilderSetNodeSize() before splitting.
     child_0->SizeRef = child_1->SizeRef = parent_node->Size;
     child_0->SizeRef[split_axis] = ImFloor(size_avail * split_ratio);
     child_1->SizeRef[split_axis] = ImFloor(size_avail - child_0->SizeRef[split_axis]);
@@ -12476,7 +12477,6 @@ ImGuiID ImGui::DockBuilderAddNode(ImGuiID id, ImGuiDockNodeFlags flags)
     {
         DockSpace(id, ImVec2(0, 0), flags | ImGuiDockNodeFlags_KeepAliveOnly);
         node = DockContextFindNodeByID(ctx, id);
-        node->LastFrameAlive = -1;
     }
     else
     {
@@ -12484,8 +12484,8 @@ ImGuiID ImGui::DockBuilderAddNode(ImGuiID id, ImGuiDockNodeFlags flags)
             node = DockContextFindNodeByID(ctx, id);
         if (!node)
             node = DockContextAddNode(ctx, id);
-        node->LastFrameAlive = ctx->FrameCount;
     }
+    node->LastFrameAlive = ctx->FrameCount;   // Set this otherwise BeginDocked will undock during the same frame.
     return node->ID;
 }