feat(xcui): add tab strip and workspace compose foundations

tests/UI/Core/unit/CMakeLists.txt

@@ -2,6 +2,8 @@ set(CORE_UI_TEST_SOURCES
     ${CMAKE_SOURCE_DIR}/tests/UI/Core/unit/test_ui_shortcut_scope.cpp
     ${CMAKE_SOURCE_DIR}/tests/UI/Core/unit/test_ui_splitter_layout.cpp
     ${CMAKE_SOURCE_DIR}/tests/UI/Core/unit/test_ui_splitter_interaction.cpp
+    ${CMAKE_SOURCE_DIR}/tests/UI/Core/unit/test_ui_tab_strip_layout.cpp
+    ${CMAKE_SOURCE_DIR}/tests/UI/Core/unit/test_ui_tab_strip_model.cpp
     # Migration bridge: legacy XCUI unit coverage still lives under tests/Core/UI
     # until it is moved into tests/UI/Core/unit without changing behavior.
     ${CMAKE_SOURCE_DIR}/tests/Core/UI/test_ui_core.cpp

tests/UI/Core/unit/test_ui_tab_strip_layout.cpp

@@ -0,0 +1,72 @@
+#include <gtest/gtest.h>
+
+#include <XCEngine/UI/Layout/UITabStripLayout.h>
+
+namespace {
+
+using XCEngine::UI::UIRect;
+using XCEngine::UI::UISize;
+using XCEngine::UI::Layout::ArrangeUITabStrip;
+using XCEngine::UI::Layout::MeasureUITabStrip;
+using XCEngine::UI::Layout::MeasureUITabStripHeaderWidth;
+using XCEngine::UI::Layout::UITabStripMeasureItem;
+using XCEngine::UI::Layout::UITabStripMetrics;
+
+void ExpectRect(
+    const UIRect& rect,
+    float x,
+    float y,
+    float width,
+    float height) {
+    EXPECT_FLOAT_EQ(rect.x, x);
+    EXPECT_FLOAT_EQ(rect.y, y);
+    EXPECT_FLOAT_EQ(rect.width, width);
+    EXPECT_FLOAT_EQ(rect.height, height);
+}
+
+} // namespace
+
+TEST(UITabStripLayoutTest, MeasureUsesTallestContentAndWidestHeaderBudget) {
+    const UITabStripMetrics metrics = { 32.0f, 80.0f, 10.0f, 2.0f };
+    const auto measured = MeasureUITabStrip(
+        {
+            UITabStripMeasureItem{ 36.0f, UISize(220.0f, 140.0f), UISize(120.0f, 80.0f) },
+            UITabStripMeasureItem{ 96.0f, UISize(180.0f, 200.0f), UISize(160.0f, 90.0f) }
+        },
+        metrics);
+
+    const float desiredHeaderWidth =
+        MeasureUITabStripHeaderWidth(36.0f, metrics) +
+        MeasureUITabStripHeaderWidth(96.0f, metrics) +
+        metrics.tabGap;
+    const float minimumHeaderWidth = metrics.tabMinWidth * 2.0f + metrics.tabGap;
+
+    EXPECT_FLOAT_EQ(measured.desiredSize.width, 220.0f);
+    EXPECT_FLOAT_EQ(measured.desiredSize.height, metrics.headerHeight + 200.0f);
+    EXPECT_FLOAT_EQ(measured.minimumSize.width, minimumHeaderWidth);
+    EXPECT_FLOAT_EQ(measured.minimumSize.height, metrics.headerHeight + 90.0f);
+}
+
+TEST(UITabStripLayoutTest, MeasureWithoutItemsReturnsZeroSize) {
+    const auto measured = MeasureUITabStrip({}, UITabStripMetrics{});
+
+    EXPECT_FLOAT_EQ(measured.desiredSize.width, 0.0f);
+    EXPECT_FLOAT_EQ(measured.desiredSize.height, 0.0f);
+    EXPECT_FLOAT_EQ(measured.minimumSize.width, 0.0f);
+    EXPECT_FLOAT_EQ(measured.minimumSize.height, 0.0f);
+}
+
+TEST(UITabStripLayoutTest, ArrangeScalesHeadersToAvailableWidthAndReservesContentArea) {
+    const UITabStripMetrics metrics = { 30.0f, 72.0f, 12.0f, 4.0f };
+    const auto arranged = ArrangeUITabStrip(
+        UIRect(10.0f, 20.0f, 180.0f, 120.0f),
+        { 120.0f, 100.0f },
+        metrics);
+
+    ExpectRect(arranged.headerRect, 10.0f, 20.0f, 180.0f, 30.0f);
+    ExpectRect(arranged.contentRect, 10.0f, 50.0f, 180.0f, 90.0f);
+    ASSERT_EQ(arranged.tabHeaderRects.size(), 2u);
+    EXPECT_NEAR(arranged.tabHeaderRects[0].width + arranged.tabHeaderRects[1].width, 176.0f, 0.001f);
+    ExpectRect(arranged.tabHeaderRects[0], 10.0f, 20.0f, 96.0f, 30.0f);
+    ExpectRect(arranged.tabHeaderRects[1], 110.0f, 20.0f, 80.0f, 30.0f);
+}

tests/UI/Core/unit/test_ui_tab_strip_model.cpp

@@ -0,0 +1,53 @@
+#include <gtest/gtest.h>
+
+#include <XCEngine/UI/Widgets/UITabStripModel.h>
+
+namespace {
+
+using XCEngine::UI::Widgets::UITabStripModel;
+
+} // namespace
+
+TEST(UITabStripModelTest, SetItemCountInitializesAndClampsSelection) {
+    UITabStripModel model = {};
+
+    EXPECT_TRUE(model.SetItemCount(3u));
+    EXPECT_TRUE(model.HasSelection());
+    EXPECT_EQ(model.GetSelectedIndex(), 0u);
+
+    EXPECT_TRUE(model.SetSelectedIndex(2u));
+    EXPECT_EQ(model.GetSelectedIndex(), 2u);
+
+    EXPECT_TRUE(model.SetItemCount(2u));
+    EXPECT_EQ(model.GetSelectedIndex(), 1u);
+}
+
+TEST(UITabStripModelTest, NextPreviousFirstAndLastStayWithinBounds) {
+    UITabStripModel model = {};
+    ASSERT_TRUE(model.SetItemCount(3u));
+
+    EXPECT_TRUE(model.SelectLast());
+    EXPECT_EQ(model.GetSelectedIndex(), 2u);
+    EXPECT_FALSE(model.SelectNext());
+    EXPECT_EQ(model.GetSelectedIndex(), 2u);
+
+    EXPECT_TRUE(model.SelectPrevious());
+    EXPECT_EQ(model.GetSelectedIndex(), 1u);
+    EXPECT_TRUE(model.SelectFirst());
+    EXPECT_EQ(model.GetSelectedIndex(), 0u);
+    EXPECT_FALSE(model.SelectPrevious());
+    EXPECT_EQ(model.GetSelectedIndex(), 0u);
+}
+
+TEST(UITabStripModelTest, RejectsOutOfRangeSelectionAndClearsWhenEmpty) {
+    UITabStripModel model = {};
+    ASSERT_TRUE(model.SetItemCount(2u));
+
+    EXPECT_FALSE(model.SetSelectedIndex(3u));
+    EXPECT_EQ(model.GetSelectedIndex(), 0u);
+
+    EXPECT_TRUE(model.SetItemCount(0u));
+    EXPECT_FALSE(model.HasSelection());
+    EXPECT_EQ(model.GetSelectedIndex(), UITabStripModel::InvalidIndex);
+    EXPECT_FALSE(model.SetSelectedIndex(0u));
+}