Fix TreeNodes in ObjectSelectionTree not remembering their open status

Previously, the id of each TreeNode was incremental which resulted in
ids changing when nodes where moved.

Author: Birdy2014

include/core/Scene.hpp

@@ -33,6 +33,9 @@ struct InstancedNode {
     std::vector<std::unique_ptr<InstancedNode>> children;
     std::string name;
 
+    static unsigned int counter;
+    unsigned int const id{counter++};
+
     void traverse(std::function<void(glm::mat4, Node const&)>) const;
     void compute_transforms(glm::mat4 = glm::mat4{1.0f});
 

include/ui/ObjectSelectionTree.hpp

@@ -10,5 +10,4 @@ struct ObjectSelectionTree {
 
 private:
     std::optional<ImRect> m_prev_rect;
-    int m_imgui_treenode_id;
 };

src/core/Scene.cpp

@@ -2,6 +2,8 @@
 
 #include <glm/ext/matrix_transform.hpp>
 
+unsigned int InstancedNode::counter = 0;
+
 glm::mat4 Transform::get_local_matrix() const
 {
     auto matrix = glm::mat4{1.0f};

src/ui/ObjectSelectionTree.cpp

@@ -46,7 +46,7 @@ void ObjectSelectionTree::traverse_nodes(InstancedNode& root)
             ? ImGuiTreeNodeFlags_Selected
             : ImGuiTreeNodeFlags_None;
 
-        auto const treenode_label = child->name + "##node_" + std::to_string(m_imgui_treenode_id++);
+        auto const treenode_label = child->name + "##node_" + std::to_string(child->id);
 
         if (!child->children.empty()) {
             open = ImGui::TreeNodeEx(treenode_label.c_str(), flags_selected);
@@ -135,7 +135,6 @@ void ObjectSelectionTree::render()
         if (auto& scene = Project::get_current()->scene; scene) {
             if (ImGui::BeginTable("table0", 1)) {
                 m_prev_rect = {};
-                m_imgui_treenode_id = 0;
                 traverse_nodes(*scene);
             }
             ImGui::EndTable();