Extract XCUI selection model and layout lab click selection

docs/plan/XCUI_Phase_Status_2026-04-05.md

@@ -32,6 +32,7 @@ Old `editor` replacement is explicitly out of scope for this phase.
 - Shared text-editing primitives now live under `engine/include/XCEngine/UI/Text` and `engine/src/UI/Text`, so UTF-8 caret movement, line splitting, and multiline navigation are no longer trapped inside `XCUI Demo`.
 - Shared text-input controller/state now also lives under `engine/include/XCEngine/UI/Text` and `engine/src/UI/Text`, so character insertion, backspace/delete, submit, and multiline key handling no longer need to be reimplemented per host.
 - Shared editor collection primitive classification and metric helpers now also live under `engine/include/XCEngine/UI/Widgets` and `engine/src/UI/Widgets`, covering the current `ScrollView` / `TreeView` / `ListView` / `PropertySection` / `FieldRow` prototype taxonomy.
+- Shared single-selection state now also lives under `engine/include/XCEngine/UI/Widgets` and `engine/src/UI/Widgets` as `UISelectionModel`, so collection-style widget selection no longer has to stay private to `LayoutLab`.
 - Core regression coverage now includes `UIContext`, layout, style, runtime screen player/system, and real document-host tests through `core_ui_tests`.
 
 Current gap:
@@ -66,6 +67,7 @@ Current gap:
 - `LayoutLab` now includes a `ScrollView` prototype and a more editor-like three-column authored layout.
 - `LayoutLab` now also covers editor-facing widget prototypes: `TreeView`, `TreeItem`, `ListView`, `ListItem`, `PropertySection`, and `FieldRow`.
 - `LayoutLab` now consumes the shared `UIEditorCollectionPrimitives` helper layer for collection-widget tag classification, clipping flags, and default metric resolution instead of keeping that taxonomy private to the sandbox runtime.
+- `LayoutLab` now also consumes the shared `UISelectionModel` for click-selection persistence across collection-style widgets, and the diagnostics panel now exposes both hovered and selected element ids.
 - Panel diagnostics were expanded to clearly separate preview/runtime/input state and native vs legacy paths.
 - The editor bridge layer now has smoke coverage for swapchain after-UI rendering hooks and SRV-backed ImGui texture descriptor registration.
 - `Application` no longer owns the ImGui backend directly; window presentation now routes through `IWindowUICompositor` with an `ImGuiWindowUICompositor` implementation, which currently delegates to `IEditorHostCompositor` / `ImGuiHostCompositor`.
@@ -78,17 +80,17 @@ Current gap:
 
 - The shell is still ImGui-hosted.
 - Legacy hosted preview still depends on an active ImGui window context for inline presentation.
-- Editor-specialized widgets are still incomplete at the shared-module level: the authored prototypes exist, but virtualization, selection models, command routing, property editing models, toolbar/menu chrome, and icon-atlas widgets are not yet extracted into reusable XCUI modules.
+- Editor-specialized widgets are still incomplete at the shared-module level: the authored prototypes exist, but virtualization, multi-selection/tree expansion state, command routing, property editing models, toolbar/menu chrome, and icon-atlas widgets are not yet extracted into reusable XCUI modules.
 
 ## Validated This Phase
 
 - `new_editor_xcui_demo_runtime_tests`: `7/7`
-- `new_editor_xcui_layout_lab_runtime_tests`: `6/6`
+- `new_editor_xcui_layout_lab_runtime_tests`: `7/7`
 - `new_editor_xcui_rhi_command_compiler_tests`: `6/6`
 - `new_editor_xcui_rhi_render_backend_tests`: `5/5`
 - `new_editor_xcui_hosted_preview_presenter_tests`: `12/12`
 - `XCNewEditor` Debug target builds successfully
-- `core_ui_tests`: `28/28`
+- `core_ui_tests`: `30/30`
 - `scene_tests`: `65/65`
 - `core_ui_style_tests`: `5/5`
 - `ui_resource_tests`: `11/11`
@@ -101,6 +103,7 @@ Current gap:
 - Common-core `UITextEditing` extraction now owns UTF-8 offset stepping, codepoint counting, line splitting, and vertical caret motion with dedicated `core_ui_tests` coverage.
 - Common-core `UITextInputController` extraction now owns per-field text state, character insertion, enter-submit, and multiline keyboard editing behavior with dedicated `core_ui_tests` coverage.
 - Common-core `UIEditorCollectionPrimitives` extraction now owns the editor collection tag taxonomy and default metric resolution used by current `LayoutLab` widget prototypes, with dedicated `core_ui_tests` coverage.
+- Common-core `UISelectionModel` extraction now owns reusable single-selection state for collection-style widgets, with dedicated `core_ui_tests` coverage.
 - Demo runtime text editing was extended with:
   - click-to-place caret
   - `Delete` support
@@ -109,6 +112,7 @@ Current gap:
 - Demo authored resources updated to exercise the input field.
 - LayoutLab `ScrollView` prototype with clipping and hover rejection outside clipped content.
 - LayoutLab editor-widget prototypes for tree/list/property-style sections with dedicated runtime coverage.
+- LayoutLab click-selection now persists through the shared `UISelectionModel`, including selected-state diagnostics and reusable visual selection feedback on cards, collection rows, and field rows.
 - Schema document support extended with:
   - retained `UISchemaDefinition` data on `UIDocumentModel`
   - artifact schema version bump for UI documents

engine/CMakeLists.txt

@@ -521,7 +521,9 @@ add_library(XCEngine STATIC
     ${CMAKE_CURRENT_SOURCE_DIR}/src/UI/Text/UITextEditing.cpp
     ${CMAKE_CURRENT_SOURCE_DIR}/src/UI/Text/UITextInputController.cpp
     ${CMAKE_CURRENT_SOURCE_DIR}/include/XCEngine/UI/Widgets/UIEditorCollectionPrimitives.h
+    ${CMAKE_CURRENT_SOURCE_DIR}/include/XCEngine/UI/Widgets/UISelectionModel.h
     ${CMAKE_CURRENT_SOURCE_DIR}/src/UI/Widgets/UIEditorCollectionPrimitives.cpp
+    ${CMAKE_CURRENT_SOURCE_DIR}/src/UI/Widgets/UISelectionModel.cpp
     ${CMAKE_CURRENT_SOURCE_DIR}/include/XCEngine/UI/Runtime/UIScreenTypes.h
     ${CMAKE_CURRENT_SOURCE_DIR}/include/XCEngine/UI/Runtime/UIScreenDocumentHost.h
     ${CMAKE_CURRENT_SOURCE_DIR}/include/XCEngine/UI/Runtime/UIScreenPlayer.h

engine/include/XCEngine/UI/Widgets/UISelectionModel.h

@@ -0,0 +1,26 @@
+#pragma once
+
+#include <string>
+#include <string_view>
+
+namespace XCEngine {
+namespace UI {
+namespace Widgets {
+
+class UISelectionModel {
+public:
+    bool HasSelection() const;
+    const std::string& GetSelectedId() const;
+    bool IsSelected(std::string_view id) const;
+
+    bool SetSelection(std::string selectionId);
+    bool ClearSelection();
+    bool ToggleSelection(std::string selectionId);
+
+private:
+    std::string m_selectedId = {};
+};
+
+} // namespace Widgets
+} // namespace UI
+} // namespace XCEngine

engine/src/UI/Widgets/UISelectionModel.cpp

@@ -0,0 +1,49 @@
+#include <XCEngine/UI/Widgets/UISelectionModel.h>
+
+namespace XCEngine {
+namespace UI {
+namespace Widgets {
+
+bool UISelectionModel::HasSelection() const {
+    return !m_selectedId.empty();
+}
+
+const std::string& UISelectionModel::GetSelectedId() const {
+    return m_selectedId;
+}
+
+bool UISelectionModel::IsSelected(std::string_view id) const {
+    return !m_selectedId.empty() && m_selectedId == id;
+}
+
+bool UISelectionModel::SetSelection(std::string selectionId) {
+    if (m_selectedId == selectionId) {
+        return false;
+    }
+
+    m_selectedId = std::move(selectionId);
+    return true;
+}
+
+bool UISelectionModel::ClearSelection() {
+    if (m_selectedId.empty()) {
+        return false;
+    }
+
+    m_selectedId.clear();
+    return true;
+}
+
+bool UISelectionModel::ToggleSelection(std::string selectionId) {
+    if (m_selectedId == selectionId) {
+        m_selectedId.clear();
+        return true;
+    }
+
+    m_selectedId = std::move(selectionId);
+    return true;
+}
+
+} // namespace Widgets
+} // namespace UI
+} // namespace XCEngine

new_editor/src/XCUIBackend/XCUILayoutLabRuntime.cpp

@@ -9,6 +9,7 @@
 #include <XCEngine/UI/Style/Theme.h>
 #include <XCEngine/UI/Types.h>
 #include <XCEngine/UI/Widgets/UIEditorCollectionPrimitives.h>
+#include <XCEngine/UI/Widgets/UISelectionModel.h>
 
 #include <algorithm>
 #include <cstdlib>
@@ -77,6 +78,7 @@ struct RuntimeBuildContext {
     std::vector<LayoutNode> nodes = {};
     std::unordered_map<std::string, std::size_t> nodeIndexById = {};
     std::unordered_map<std::string, UIRect> rectsById = {};
+    UIWidgets::UISelectionModel selectionModel = {};
     bool documentsReady = false;
     std::string statusMessage = {};
     XCUIAssetDocumentSource documentSource = XCUIAssetDocumentSource(
@@ -752,6 +754,7 @@ void DrawNode(
                 bodyFont);
         }
     } else if (node.tagName == "Card") {
+        const bool selected = state.selectionModel.IsSelected(node.id);
         const Color cardColor = ResolveColorToken(
             state.theme,
             node.tone == "accent"
@@ -799,17 +802,25 @@ void DrawNode(
                 UIColor(1.0f, 0.82f, 0.45f, 1.0f),
                 2.0f,
                 rounding);
+        } else if (selected) {
+            drawList.AddRectOutline(
+                node.rect,
+                ToUIColor(ResolveColorToken(state.theme, "color.accent", Color(0.30f, 0.46f, 0.58f, 1.0f))),
+                2.0f,
+                rounding);
         }
     } else if (primitiveKind == UIWidgets::UIEditorCollectionPrimitiveKind::TreeItem ||
         primitiveKind == UIWidgets::UIEditorCollectionPrimitiveKind::ListItem) {
         const bool hovered = node.id == hoveredId;
-        const Color rowColor = hovered
+        const bool selected = state.selectionModel.IsSelected(node.id);
+        const Color rowColor = selected
+            ? ResolveColorToken(state.theme, "color.accent", Color(0.30f, 0.46f, 0.58f, 1.0f))
+            : (hovered
                 ? ResolveColorToken(state.theme, "color.card.alt", Color(0.20f, 0.27f, 0.34f, 1.0f))
-            : ResolveColorToken(state.theme, "color.card", Color(0.12f, 0.17f, 0.23f, 1.0f));
-        const Color borderColor = ResolveColorToken(
-            state.theme,
-            "color.border",
-            Color(0.24f, 0.34f, 0.43f, 1.0f));
+                : ResolveColorToken(state.theme, "color.card", Color(0.12f, 0.17f, 0.23f, 1.0f)));
+        const Color borderColor = selected
+            ? ResolveColorToken(state.theme, "color.accent", Color(0.30f, 0.46f, 0.58f, 1.0f))
+            : ResolveColorToken(state.theme, "color.border", Color(0.24f, 0.34f, 0.43f, 1.0f));
         const Color textColor = ResolveColorToken(
             state.theme,
             "color.text",
@@ -848,6 +859,7 @@ void DrawNode(
         }
     } else if (primitiveKind == UIWidgets::UIEditorCollectionPrimitiveKind::FieldRow) {
         const bool hovered = node.id == hoveredId;
+        const bool selected = state.selectionModel.IsSelected(node.id);
         const Color textColor = ResolveColorToken(
             state.theme,
             "color.text",
@@ -856,7 +868,7 @@ void DrawNode(
             state.theme,
             "color.text.muted",
             Color(0.72f, 0.79f, 0.86f, 1.0f));
-        const Color lineColor = hovered
+        const Color lineColor = selected || hovered
             ? ResolveColorToken(state.theme, "color.accent", Color(0.30f, 0.46f, 0.58f, 1.0f))
             : ResolveColorToken(state.theme, "color.border", Color(0.24f, 0.34f, 0.43f, 1.0f));
         const float inset = ResolveFloatToken(state.theme, "space.cardInset", 12.0f);
@@ -955,6 +967,7 @@ bool XCUILayoutLabRuntime::ReloadDocuments() {
     state.nodes.clear();
     state.nodeIndexById.clear();
     state.rectsById.clear();
+    state.selectionModel.ClearSelection();
 
     state.documentSource.SetPathSet(XCUIAssetDocumentSource::MakeLayoutLabPathSet());
     if (!state.documentSource.Reload()) {
@@ -1027,13 +1040,24 @@ const XCUILayoutLabFrameResult& XCUILayoutLabRuntime::Update(const XCUILayoutLab
         state.rectsById[state.nodes[0].id] = state.nodes[0].rect;
     }
 
+    std::size_t hoveredIndex = kInvalidIndex;
     if (input.pointerInside) {
-        const std::size_t hoveredIndex = HitTest(state, input.pointerPosition);
+        hoveredIndex = HitTest(state, input.pointerPosition);
         if (hoveredIndex != kInvalidIndex) {
             state.frameResult.stats.hoveredElementId = state.nodes[hoveredIndex].id;
         }
     }
 
+    if (input.pointerPressed) {
+        if (hoveredIndex != kInvalidIndex) {
+            state.selectionModel.SetSelection(state.nodes[hoveredIndex].id);
+        } else {
+            state.selectionModel.ClearSelection();
+        }
+    }
+
+    state.frameResult.stats.selectedElementId = state.selectionModel.GetSelectedId();
+
     UIDrawList drawList("XCUI Layout Lab");
     drawList.PushClipRect(input.canvasRect);
     DrawNode(state, 0u, drawList, state.frameResult.stats.hoveredElementId);

new_editor/src/XCUIBackend/XCUILayoutLabRuntime.h

@@ -17,6 +17,7 @@ struct XCUILayoutLabInputState {
     UI::UIRect canvasRect = {};
     UI::UIPoint pointerPosition = {};
     bool pointerInside = false;
+    bool pointerPressed = false;
 };
 
 struct XCUILayoutLabFrameStats {
@@ -47,6 +48,7 @@ struct XCUILayoutLabFrameStats {
     std::size_t propertySectionCount = 0;
     std::size_t fieldRowCount = 0;
     std::string hoveredElementId = {};
+    std::string selectedElementId = {};
 };
 
 struct XCUILayoutLabFrameResult {

new_editor/src/panels/XCUILayoutLabPanel.cpp

@@ -241,6 +241,7 @@ void XCUILayoutLabPanel::Render() {
         input.pointerPosition = UI::UIPoint(ImGui::GetIO().MousePos.x, ImGui::GetIO().MousePos.y);
         input.pointerInside = validCanvas && ImGui::IsItemHovered();
     }
+    input.pointerPressed = input.pointerInside && ImGui::IsMouseClicked(ImGuiMouseButton_Left);
 
     const ::XCEngine::Editor::XCUIBackend::XCUILayoutLabFrameResult& frame = m_runtime.Update(input);
 
@@ -337,17 +338,19 @@ void XCUILayoutLabPanel::Render() {
         "Native note: %s",
         stats.nativeOverlayStatusMessage.empty() ? "none" : stats.nativeOverlayStatusMessage.c_str());
     ImGui::Text(
-        "Hovered: %s | canvas: %.0f x %.0f",
+        "Hovered: %s | Selected: %s | canvas: %.0f x %.0f",
         stats.hoveredElementId.empty() ? "none" : stats.hoveredElementId.c_str(),
+        stats.selectedElementId.empty() ? "none" : stats.selectedElementId.c_str(),
         input.canvasRect.width,
         input.canvasRect.height);
 
     ImGui::SeparatorText("Input");
     ImGui::Text(
-        "Pointer: %.0f, %.0f | inside %s",
+        "Pointer: %.0f, %.0f | inside %s | pressed %s",
         input.pointerPosition.x,
         input.pointerPosition.y,
-        input.pointerInside ? "yes" : "no");
+        input.pointerInside ? "yes" : "no",
+        input.pointerPressed ? "yes" : "no");
     ImGui::EndChild();
 
     ImGui::End();

tests/Core/UI/CMakeLists.txt

@@ -6,6 +6,7 @@ set(UI_TEST_SOURCES
     test_ui_core.cpp
     test_ui_editor_collection_primitives.cpp
     test_layout_engine.cpp
+    test_ui_selection_model.cpp
     test_ui_runtime.cpp
     test_ui_text_editing.cpp
     test_ui_text_input_controller.cpp

tests/Core/UI/test_ui_selection_model.cpp

@@ -0,0 +1,42 @@
+#include <gtest/gtest.h>
+
+#include <XCEngine/UI/Widgets/UISelectionModel.h>
+
+namespace {
+
+using XCEngine::UI::Widgets::UISelectionModel;
+
+TEST(UISelectionModelTest, SetAndClearSelectionTrackCurrentId) {
+    UISelectionModel selection = {};
+
+    EXPECT_FALSE(selection.HasSelection());
+    EXPECT_TRUE(selection.GetSelectedId().empty());
+
+    EXPECT_TRUE(selection.SetSelection("assetLighting"));
+    EXPECT_TRUE(selection.HasSelection());
+    EXPECT_TRUE(selection.IsSelected("assetLighting"));
+    EXPECT_EQ(selection.GetSelectedId(), "assetLighting");
+
+    EXPECT_FALSE(selection.SetSelection("assetLighting"));
+    EXPECT_TRUE(selection.ClearSelection());
+    EXPECT_FALSE(selection.HasSelection());
+    EXPECT_TRUE(selection.GetSelectedId().empty());
+    EXPECT_FALSE(selection.ClearSelection());
+}
+
+TEST(UISelectionModelTest, ToggleSelectionSelectsAndDeselectsMatchingId) {
+    UISelectionModel selection = {};
+
+    EXPECT_TRUE(selection.ToggleSelection("treeScenes"));
+    EXPECT_EQ(selection.GetSelectedId(), "treeScenes");
+
+    EXPECT_TRUE(selection.ToggleSelection("treeScenes"));
+    EXPECT_TRUE(selection.GetSelectedId().empty());
+
+    EXPECT_TRUE(selection.ToggleSelection("treeMaterials"));
+    EXPECT_EQ(selection.GetSelectedId(), "treeMaterials");
+    EXPECT_TRUE(selection.ToggleSelection("treeUi"));
+    EXPECT_EQ(selection.GetSelectedId(), "treeUi");
+}
+
+} // namespace

tests/NewEditor/test_xcui_layout_lab_runtime.cpp

@@ -216,3 +216,37 @@ TEST(NewEditorXCUILayoutLabRuntimeTest, HoverIgnoresClippedScrollViewContent) {
     ASSERT_TRUE(frame.stats.documentsReady);
     EXPECT_TRUE(frame.stats.hoveredElementId.empty());
 }
+
+TEST(NewEditorXCUILayoutLabRuntimeTest, ClickSelectionPersistsOnSharedCollectionItems) {
+    XCEngine::Editor::XCUIBackend::XCUILayoutLabRuntime runtime;
+    ASSERT_TRUE(runtime.ReloadDocuments());
+
+    const auto& baseline = runtime.Update(BuildInputState());
+    ASSERT_TRUE(baseline.stats.documentsReady);
+
+    XCEngine::UI::UIRect targetRect = {};
+    ASSERT_TRUE(runtime.TryGetElementRect("fieldPosition", targetRect));
+
+    XCEngine::Editor::XCUIBackend::XCUILayoutLabInputState clickInput = BuildInputState();
+    clickInput.pointerPosition = XCEngine::UI::UIPoint(
+        targetRect.x + targetRect.width * 0.5f,
+        targetRect.y + targetRect.height * 0.5f);
+    clickInput.pointerPressed = true;
+    const auto& selectedFrame = runtime.Update(clickInput);
+
+    ASSERT_TRUE(selectedFrame.stats.documentsReady);
+    ASSERT_FALSE(selectedFrame.stats.hoveredElementId.empty());
+    EXPECT_EQ(
+        selectedFrame.stats.selectedElementId,
+        selectedFrame.stats.hoveredElementId);
+
+    const std::string selectedElementId = selectedFrame.stats.selectedElementId;
+    XCEngine::UI::UIRect selectedRect = {};
+    EXPECT_TRUE(runtime.TryGetElementRect(selectedElementId, selectedRect));
+    EXPECT_GT(selectedRect.width, 0.0f);
+    EXPECT_GT(selectedRect.height, 0.0f);
+
+    const auto& persistedFrame = runtime.Update(BuildInputState());
+    ASSERT_TRUE(persistedFrame.stats.documentsReady);
+    EXPECT_EQ(persistedFrame.stats.selectedElementId, selectedElementId);
+}