Add expand/collapse support to TreeView

CHANGELOG.md

@@ -70,6 +70,7 @@
 -   Fix linker error "library limit of 65535 objects exceeded" with Ninja generator on MSVC (PR #7335)
 -   Download tarballs instead of Git repos for "3rdparty/uvatlas" (PR #7371)
 -   macOS x86_64 not longer supported, only macOS arm64 is supported.
+-   Add expand/collapse state support for TreeView items in GUI (PR #7451)
 
 
 ## 0.13

cpp/open3d/visualization/gui/TreeView.cpp

@@ -11,6 +11,7 @@
 
 #include <cmath>
 #include <list>
+#include <optional>
 #include <sstream>
 #include <unordered_map>
 
@@ -212,6 +213,7 @@ struct TreeView::Impl {
         std::shared_ptr<Widget> cell;
         Item *parent = nullptr;
         std::list<Item> children;
+        std::optional<bool> expanded;
     };
     int id_;
     Item root_;
@@ -361,6 +363,22 @@ void TreeView::Layout(const LayoutContext &context) {
     // to defer layout to Draw().
 }
 
+bool TreeView::IsItemExpanded(ItemId item_id) const {
+    auto it = impl_->id2item_.find(item_id);
+    if (it == impl_->id2item_.end()) {
+        return false;
+    }
+    return it->second->expanded.value_or(true);
+}
+
+void TreeView::SetItemExpanded(ItemId item_id, bool expanded) {
+    auto it = impl_->id2item_.find(item_id);
+    if (it == impl_->id2item_.end()) {
+        return;
+    }
+    it->second->expanded = expanded;
+}
+
 Widget::DrawResult TreeView::Draw(const DrawContext &context) {
     auto result = Widget::DrawResult::NONE;
     auto &frame = GetFrame();
@@ -417,8 +435,12 @@ Widget::DrawResult TreeView::Draw(const DrawContext &context) {
                     colorToImguiRGBA(context.theme.tree_selected_color));
         }
 
-        int flags = ImGuiTreeNodeFlags_DefaultOpen |
-                    ImGuiTreeNodeFlags_AllowItemOverlap;
+        int flags = ImGuiTreeNodeFlags_AllowItemOverlap;
+        bool expanded = item.expanded.value_or(true);
+
+        if (expanded) {
+            flags |= ImGuiTreeNodeFlags_DefaultOpen;
+        }
         if (impl_->can_select_parents_) {
             flags |= ImGuiTreeNodeFlags_OpenOnDoubleClick;
             flags |= ImGuiTreeNodeFlags_OpenOnArrow;
@@ -465,7 +487,10 @@ Widget::DrawResult TreeView::Draw(const DrawContext &context) {
             }
         };
 
-        if (ImGui::TreeNodeEx(item.id_string.c_str(), flags, "%s", "")) {
+        bool open = ImGui::TreeNodeEx(item.id_string.c_str(), flags, "%s", "");
+        item.expanded = open;
+
+        if (open) {
             DrawThis(item, height, is_selectable);
 
             for (auto &child : item.children) {

cpp/open3d/visualization/gui/TreeView.h

@@ -134,6 +134,9 @@ class TreeView : public Widget {
     void SetOnSelectionChanged(
             std::function<void(ItemId)> on_selection_changed);
 
+    bool IsItemExpanded(ItemId item_id) const;
+    void SetItemExpanded(ItemId item_id, bool expanded);
+
 private:
     struct Impl;
     std::unique_ptr<Impl> impl_;

cpp/pybind/visualization/gui/gui.cpp

@@ -1664,7 +1664,9 @@ void pybind_gui_definitions(py::module &m) {
                           "The currently selected item")
             .def("set_on_selection_changed", &TreeView::SetOnSelectionChanged,
                  "Sets f(new_item_id) which is called when the user "
-                 "changes the selection.");
+                 "changes the selection.")
+            .def("is_item_expanded", &TreeView::IsItemExpanded)
+            .def("set_item_expanded", &TreeView::SetItemExpanded);
 
     // ---- TreeView cells ----
     auto checkable_cell = static_cast<

cpp/tests/visualization/CMakeLists.txt

@@ -3,3 +3,17 @@ if (BUILD_GUI)
         rendering/MaterialModifier.cpp
     )
 endif()
+
+
+add_executable(TreeViewTest
+    TreeViewTest.cpp
+)
+
+target_link_libraries(TreeViewTest
+    PRIVATE
+        Open3D::Open3D
+)
+
+set_target_properties(TreeViewTest PROPERTIES
+    RUNTIME_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR}/bin
+)

cpp/tests/visualization/TreeViewTest.cpp

@@ -0,0 +1,45 @@
+#include <thread>
+#include <chrono>
+
+#include "open3d/visualization/gui/Application.h"
+#include "open3d/visualization/gui/Window.h"
+#include "open3d/visualization/gui/TreeView.h"
+#include "open3d/visualization/gui/Layout.h"
+
+using namespace open3d::visualization::gui;
+
+int main() {
+    auto& app = Application::GetInstance();
+    app.Initialize();
+
+    auto window = std::make_shared<Window>("TreeView GUI Test", 400, 300);
+
+    // Layout
+    auto layout = std::make_shared<Vert>(10);  // spacing = 10
+
+    // TreeView
+    auto tree = std::make_shared<TreeView>();
+    auto root = tree->GetRootItem();
+    tree->AddTextItem(root, "Item A");
+    tree->AddTextItem(root, "Item B");
+
+    layout->AddChild(tree);
+    window->AddChild(layout);
+
+    app.AddWindow(window);
+
+    // Close automatically after 2 seconds
+    app.PostToMainThread(nullptr, []() {
+        // NOTE:
+        // This is a GUI smoke test.
+        // The window is shown briefly to ensure TreeView can be
+        // created, attached, and rendered without crashing.
+        // The application exits automatically to avoid blocking CI.
+
+        std::this_thread::sleep_for(std::chrono::seconds(2));
+        Application::GetInstance().Quit();
+    });
+
+    app.Run();
+    return 0;
+}