fix(new_editor/tab-drag): keep floating window under cursor

new_editor/app/Platform/Win32/EditorWindowManagerTabDrag.cpp

@@ -3,8 +3,34 @@
 #include "State/EditorContext.h"
 #include "EditorWindow.h"
 
+#include <algorithm>
+#include <cmath>
+
 namespace XCEngine::UI::Editor::App {
 
+namespace {
+
+constexpr LONG kFallbackDragHotspotX = 40;
+constexpr LONG kFallbackDragHotspotY = 12;
+
+POINT BuildFallbackGlobalTabDragHotspot() {
+    POINT hotspot = {};
+    hotspot.x = kFallbackDragHotspotX;
+    hotspot.y = kFallbackDragHotspotY;
+    return hotspot;
+}
+
+float ResolveWindowDpiScale(HWND hwnd) {
+    if (hwnd == nullptr) {
+        return 1.0f;
+    }
+
+    const UINT dpi = GetDpiForWindow(hwnd);
+    return dpi == 0u ? 1.0f : static_cast<float>(dpi) / 96.0f;
+}
+
+} // namespace
+
 bool EditorWindowManager::IsGlobalTabDragActive() const {
     return m_globalTabDragSession.active;
 }
@@ -18,12 +44,94 @@ void EditorWindowManager::BeginGlobalTabDragSession(
     std::string_view panelWindowId,
     std::string_view sourceNodeId,
     std::string_view panelId,
-    const POINT& screenPoint) {
+    const POINT& screenPoint,
+    const POINT& dragHotspot) {
     m_globalTabDragSession.active = true;
     m_globalTabDragSession.panelWindowId = std::string(panelWindowId);
     m_globalTabDragSession.sourceNodeId = std::string(sourceNodeId);
     m_globalTabDragSession.panelId = std::string(panelId);
     m_globalTabDragSession.screenPoint = screenPoint;
+    m_globalTabDragSession.dragHotspot = dragHotspot;
+}
+
+bool EditorWindowManager::TryResolveGlobalTabDragHotspot(
+    const EditorWindow& sourceWindow,
+    std::string_view nodeId,
+    std::string_view panelId,
+    const POINT& screenPoint,
+    POINT& outDragHotspot) const {
+    const HWND hwnd = sourceWindow.GetHwnd();
+    if (hwnd == nullptr) {
+        return false;
+    }
+
+    const auto& layout =
+        sourceWindow.GetShellFrame().workspaceInteractionFrame.dockHostFrame.layout;
+    for (const Widgets::UIEditorDockHostTabStackLayout& tabStack : layout.tabStacks) {
+        if (tabStack.nodeId != nodeId) {
+            continue;
+        }
+
+        const std::size_t tabCount =
+            (std::min)(tabStack.items.size(), tabStack.tabStripLayout.tabHeaderRects.size());
+        for (std::size_t index = 0u; index < tabCount; ++index) {
+            if (tabStack.items[index].panelId != panelId) {
+                continue;
+            }
+
+            const ::XCEngine::UI::UIPoint clientPointDips =
+                sourceWindow.ConvertScreenPixelsToClientDips(screenPoint);
+            const ::XCEngine::UI::UIRect& tabRect =
+                tabStack.tabStripLayout.tabHeaderRects[index];
+            const float dpiScale = ResolveWindowDpiScale(hwnd);
+            const float localOffsetXDips = (std::clamp)(
+                clientPointDips.x - tabRect.x,
+                0.0f,
+                (std::max)(tabRect.width, 0.0f));
+            const float localOffsetYDips = (std::clamp)(
+                clientPointDips.y - tabRect.y,
+                0.0f,
+                (std::max)(tabRect.height, 0.0f));
+            outDragHotspot.x = static_cast<LONG>(std::lround(localOffsetXDips * dpiScale));
+            outDragHotspot.y = static_cast<LONG>(std::lround(localOffsetYDips * dpiScale));
+            return true;
+        }
+    }
+
+    return false;
+}
+
+void EditorWindowManager::UpdateGlobalTabDragOwnerWindowPosition() {
+    if (!m_globalTabDragSession.active) {
+        return;
+    }
+
+    EditorWindow* ownerWindow = FindWindow(m_globalTabDragSession.panelWindowId);
+    if (ownerWindow == nullptr || ownerWindow->GetHwnd() == nullptr) {
+        return;
+    }
+
+    RECT windowRect = {};
+    if (!GetWindowRect(ownerWindow->GetHwnd(), &windowRect)) {
+        return;
+    }
+
+    const LONG targetLeft =
+        m_globalTabDragSession.screenPoint.x - m_globalTabDragSession.dragHotspot.x;
+    const LONG targetTop =
+        m_globalTabDragSession.screenPoint.y - m_globalTabDragSession.dragHotspot.y;
+    if (windowRect.left == targetLeft && windowRect.top == targetTop) {
+        return;
+    }
+
+    SetWindowPos(
+        ownerWindow->GetHwnd(),
+        nullptr,
+        targetLeft,
+        targetTop,
+        0,
+        0,
+        SWP_NOSIZE | SWP_NOZORDER | SWP_NOACTIVATE);
 }
 
 void EditorWindowManager::EndGlobalTabDragSession() {
@@ -55,6 +163,7 @@ bool EditorWindowManager::HandleGlobalTabDragPointerMove(HWND hwnd) {
     POINT screenPoint = {};
     if (GetCursorPos(&screenPoint)) {
         m_globalTabDragSession.screenPoint = screenPoint;
+        UpdateGlobalTabDragOwnerWindowPosition();
     }
     return true;
 }
@@ -82,6 +191,14 @@ bool EditorWindowManager::TryStartGlobalTabDrag(EditorWindow& sourceWindow) {
         return false;
     }
 
+    POINT dragHotspot = BuildFallbackGlobalTabDragHotspot();
+    TryResolveGlobalTabDragHotspot(
+        sourceWindow,
+        pending->nodeId,
+        pending->panelId,
+        pending->screenPoint,
+        dragHotspot);
+
     if (sourceWindow.IsPrimary()) {
         UIEditorWindowWorkspaceController windowWorkspaceController =
             BuildLiveWindowWorkspaceController(sourceWindow.GetWindowId());
@@ -115,7 +232,9 @@ bool EditorWindowManager::TryStartGlobalTabDrag(EditorWindow& sourceWindow) {
             detachedWindow->GetWindowId(),
             detachedWindow->GetWorkspaceController().GetWorkspace().root.nodeId,
             pending->panelId,
-            pending->screenPoint);
+            pending->screenPoint,
+            dragHotspot);
+        UpdateGlobalTabDragOwnerWindowPosition();
         SetCapture(detachedWindow->GetHwnd());
         SetForegroundWindow(detachedWindow->GetHwnd());
         LogRuntimeTrace(
@@ -130,7 +249,9 @@ bool EditorWindowManager::TryStartGlobalTabDrag(EditorWindow& sourceWindow) {
         sourceWindow.GetWindowId(),
         pending->nodeId,
         pending->panelId,
-        pending->screenPoint);
+        pending->screenPoint,
+        dragHotspot);
+    UpdateGlobalTabDragOwnerWindowPosition();
     if (sourceWindow.GetHwnd() != nullptr) {
         SetCapture(sourceWindow.GetHwnd());
     }