fix(new_editor/docking): restore cross-window drop preview

new_editor/app/Composition/EditorShellRuntime.cpp

@@ -65,6 +65,17 @@ const std::string& EditorShellRuntime::GetBuiltInIconError() const {
     return m_builtInIcons.GetLastError();
 }
 
+void EditorShellRuntime::SetExternalDockHostDropPreview(
+    const Widgets::UIEditorDockHostDropPreviewState& preview) {
+    m_shellInteractionState.workspaceInteractionState.dockHostInteractionState
+        .dockHostState.dropPreview = preview;
+}
+
+void EditorShellRuntime::ClearExternalDockHostDropPreview() {
+    m_shellInteractionState.workspaceInteractionState.dockHostInteractionState
+        .dockHostState.dropPreview = {};
+}
+
 ProjectPanel::CursorKind EditorShellRuntime::GetHostedContentCursorKind() const {
     return m_projectPanel.GetCursorKind();
 }

new_editor/app/Composition/EditorShellRuntime.h

@@ -53,6 +53,9 @@ public:
     const std::vector<HierarchyPanel::Event>& GetHierarchyPanelEvents() const;
     const std::vector<ProjectPanel::Event>& GetProjectPanelEvents() const;
     const std::string& GetBuiltInIconError() const;
+    void SetExternalDockHostDropPreview(
+        const Widgets::UIEditorDockHostDropPreviewState& preview);
+    void ClearExternalDockHostDropPreview();
 
     ProjectPanel::CursorKind GetHostedContentCursorKind() const;
     Widgets::UIEditorDockHostCursorKind GetDockCursorKind() const;

new_editor/app/Platform/Win32/EditorWindow.h

@@ -60,6 +60,9 @@ public:
     const UIEditorShellInteractionState& GetShellInteractionState() const;
     ::XCEngine::UI::UIPoint ConvertScreenPixelsToClientDips(const POINT& screenPoint) const;
     void InvalidateHostWindow() const;
+    void SetExternalDockHostDropPreview(
+        const Widgets::UIEditorDockHostDropPreviewState& preview);
+    void ClearExternalDockHostDropPreview();
 
     void AttachHwnd(HWND hwnd);
     void MarkDestroyed();

new_editor/app/Platform/Win32/EditorWindowLifecycle.cpp

@@ -77,6 +77,15 @@ const UIEditorShellInteractionState& EditorWindow::GetShellInteractionState() co
     return m_composition.shellRuntime.GetShellInteractionState();
 }
 
+void EditorWindow::SetExternalDockHostDropPreview(
+    const Widgets::UIEditorDockHostDropPreviewState& preview) {
+    m_composition.shellRuntime.SetExternalDockHostDropPreview(preview);
+}
+
+void EditorWindow::ClearExternalDockHostDropPreview() {
+    m_composition.shellRuntime.ClearExternalDockHostDropPreview();
+}
+
 void EditorWindow::AttachHwnd(HWND hwnd) {
     m_window.hwnd = hwnd;
 }

new_editor/app/Platform/Win32/EditorWindowManager.h

@@ -87,6 +87,7 @@ private:
         std::string panelWindowId = {};
         std::string sourceNodeId = {};
         std::string panelId = {};
+        std::string previewWindowId = {};
         POINT screenPoint = {};
         POINT dragHotspot = {};
     };
@@ -121,6 +122,8 @@ private:
         std::string_view panelId,
         const POINT& screenPoint,
         POINT& outDragHotspot) const;
+    void ClearGlobalTabDragDropPreview();
+    void UpdateGlobalTabDragDropPreview();
     void UpdateGlobalTabDragOwnerWindowPosition();
     EditorWindow* FindTopmostWindowAtScreenPoint(
         const POINT& screenPoint,

new_editor/app/Platform/Win32/EditorWindowManagerCrossWindowDropSupport.h

@@ -19,7 +19,7 @@ struct CrossWindowDockDropTarget {
     std::size_t insertionIndex = Widgets::UIEditorTabStripInvalidIndex;
 };
 
-bool TryResolveCrossWindowDockDropTarget(
+inline bool TryResolveCrossWindowDockDropTarget(
     const Widgets::UIEditorDockHostLayout& layout,
     const ::XCEngine::UI::UIPoint& point,
     CrossWindowDockDropTarget& outTarget) {

new_editor/app/Platform/Win32/EditorWindowManagerTabDrag.cpp

@@ -1,5 +1,6 @@
 #include "EditorWindowManager.h"
 
+#include "Platform/Win32/EditorWindowManagerCrossWindowDropSupport.h"
 #include "State/EditorContext.h"
 #include "EditorWindow.h"
 
@@ -10,6 +11,9 @@ namespace XCEngine::UI::Editor::App {
 
 namespace {
 
+using EditorWindowManagerCrossWindowDropSupport::CrossWindowDockDropTarget;
+using EditorWindowManagerCrossWindowDropSupport::TryResolveCrossWindowDockDropTarget;
+
 constexpr LONG kFallbackDragHotspotX = 40;
 constexpr LONG kFallbackDragHotspotY = 12;
 
@@ -134,11 +138,67 @@ void EditorWindowManager::UpdateGlobalTabDragOwnerWindowPosition() {
         SWP_NOSIZE | SWP_NOZORDER | SWP_NOACTIVATE);
 }
 
+void EditorWindowManager::ClearGlobalTabDragDropPreview() {
+    if (m_globalTabDragSession.previewWindowId.empty()) {
+        return;
+    }
+
+    if (EditorWindow* previewWindow = FindWindow(m_globalTabDragSession.previewWindowId);
+        previewWindow != nullptr) {
+        previewWindow->ClearExternalDockHostDropPreview();
+        previewWindow->InvalidateHostWindow();
+    }
+    m_globalTabDragSession.previewWindowId.clear();
+}
+
+void EditorWindowManager::UpdateGlobalTabDragDropPreview() {
+    if (!m_globalTabDragSession.active) {
+        return;
+    }
+
+    EditorWindow* targetWindow = FindTopmostWindowAtScreenPoint(
+        m_globalTabDragSession.screenPoint,
+        m_globalTabDragSession.panelWindowId);
+    if (targetWindow == nullptr || targetWindow->GetHwnd() == nullptr) {
+        ClearGlobalTabDragDropPreview();
+        return;
+    }
+
+    const ::XCEngine::UI::UIPoint targetPoint =
+        targetWindow->ConvertScreenPixelsToClientDips(m_globalTabDragSession.screenPoint);
+    const Widgets::UIEditorDockHostLayout& targetLayout =
+        targetWindow->GetShellFrame().workspaceInteractionFrame.dockHostFrame.layout;
+    CrossWindowDockDropTarget dropTarget = {};
+    if (!TryResolveCrossWindowDockDropTarget(targetLayout, targetPoint, dropTarget) ||
+        !dropTarget.valid) {
+        ClearGlobalTabDragDropPreview();
+        return;
+    }
+
+    if (!m_globalTabDragSession.previewWindowId.empty() &&
+        m_globalTabDragSession.previewWindowId != targetWindow->GetWindowId()) {
+        ClearGlobalTabDragDropPreview();
+    }
+
+    Widgets::UIEditorDockHostDropPreviewState preview = {};
+    preview.visible = true;
+    preview.sourceNodeId = m_globalTabDragSession.sourceNodeId;
+    preview.sourcePanelId = m_globalTabDragSession.panelId;
+    preview.targetNodeId = dropTarget.nodeId;
+    preview.placement = dropTarget.placement;
+    preview.insertionIndex = dropTarget.insertionIndex;
+    targetWindow->SetExternalDockHostDropPreview(preview);
+    targetWindow->InvalidateHostWindow();
+    m_globalTabDragSession.previewWindowId = std::string(targetWindow->GetWindowId());
+}
+
 void EditorWindowManager::EndGlobalTabDragSession() {
     if (!m_globalTabDragSession.active) {
         return;
     }
 
+    ClearGlobalTabDragDropPreview();
+
     if (EditorWindow* ownerWindow = FindWindow(m_globalTabDragSession.panelWindowId);
         ownerWindow != nullptr) {
         if (GetCapture() == ownerWindow->GetHwnd()) {
@@ -164,6 +224,7 @@ bool EditorWindowManager::HandleGlobalTabDragPointerMove(HWND hwnd) {
     if (GetCursorPos(&screenPoint)) {
         m_globalTabDragSession.screenPoint = screenPoint;
         UpdateGlobalTabDragOwnerWindowPosition();
+        UpdateGlobalTabDragDropPreview();
     }
     return true;
 }