From 982904e2ba1915b9edaa127da77f2cdc6c138f66 Mon Sep 17 00:00:00 2001
From: Sergio Martins <sergio.martins@kdab.com>
Date: Thu, 2 Jun 2022 15:19:01 +0100
Subject: [PATCH] Pass the DropArea to setDropIndicatorAllowedFunc() too

So the lambda can have more advanced usage and inspect the
target layout before allowing or disallowing the drop.

For our use case, we want to limit max 3 dock widgets side by side,
for example.
---
 examples/dockwidgets/main.cpp                 | 3 ++-
 src/Config.h                                  | 8 ++++++--
 src/private/DragController_p.h                | 4 +++-
 src/private/DropIndicatorOverlayInterface.cpp | 3 ++-
 4 files changed, 13 insertions(+), 5 deletions(-)

diff --git a/examples/dockwidgets/main.cpp b/examples/dockwidgets/main.cpp
index 74c724d2..2bb9cde7 100644
--- a/examples/dockwidgets/main.cpp
+++ b/examples/dockwidgets/main.cpp
@@ -267,7 +267,8 @@ int main(int argc, char **argv)
         // Dock widget 8 will only be allowed to dock to the outer areasa
         auto func = [](KDDockWidgets::DropLocation location,
                        const KDDockWidgets::DockWidgetBase::List &source,
-                       const KDDockWidgets::DockWidgetBase::List &target) {
+                       const KDDockWidgets::DockWidgetBase::List &target,
+                       KDDockWidgets::DropArea *) {
             Q_UNUSED(target); // When dragging into a tab, 'target' would have the list of already tabbed dock widgets
 
             const bool isDraggingDW8 = std::find_if(source.cbegin(), source.cend(), [] (KDDockWidgets::DockWidgetBase *dw) {
diff --git a/src/Config.h b/src/Config.h
index 2548753c..1a0b69f6 100644
--- a/src/Config.h
+++ b/src/Config.h
@@ -34,6 +34,7 @@ namespace KDDockWidgets {
 class DockWidgetBase;
 class MainWindowBase;
 class FrameworkWidgetFactory;
+class DropArea;
 
 typedef KDDockWidgets::DockWidgetBase *(*DockWidgetFactoryFunc)(const QString &name);
 typedef KDDockWidgets::MainWindowBase *(*MainWindowFactoryFunc)(const QString &name);
@@ -47,11 +48,13 @@ typedef KDDockWidgets::MainWindowBase *(*MainWindowFactoryFunc)(const QString &n
 /// @param location The drop indicator location to allow or disallow
 /// @param source The dock widgets being dragged
 /// @param target The dock widgets within an existing docked tab group
+/// @param dropArea The target drop area. Can belong to a MainWindow or a FloatingWindow.
 /// @return true if the docking is allowed.
 /// @sa setDropIndicatorAllowedFunc
 typedef bool (*DropIndicatorAllowedFunc)(DropLocation location,
                                          const QVector<DockWidgetBase *> &source,
-                                         const QVector<DockWidgetBase *> &target);
+                                         const QVector<DockWidgetBase *> &target,
+                                         DropArea *dropArea);
 
 /// @deprecated Use DropIndicatorAllowedFunc instead.
 /// @brief Function to allow the user more granularity to disallow dock widgets to tab together
@@ -262,7 +265,8 @@ public:
      *
      * auto func = [] (KDDockWidgets::DropLocation loc,
      *                 const KDDockWidgets::DockWidgetBase::List &source,
-     *                 const KDDockWidgets::DockWidgetBase::List &target)
+     *                 const KDDockWidgets::DockWidgetBase::List &target,
+     *                 KDDockWidgets::DropArea *)
      * {
      *    // disallows dockFoo to be docked to outer areas
      *    return !((loc & KDDockWidgets::DropLocation_Outter) && source.contains(dockFoo));
diff --git a/src/private/DragController_p.h b/src/private/DragController_p.h
index 58efa3c3..e361e6fc 100644
--- a/src/private/DragController_p.h
+++ b/src/private/DragController_p.h
@@ -96,6 +96,9 @@ public:
 
     FloatingWindow *floatingWindowBeingDragged() const;
 
+    /// @brief Returns the current drop area under the mouse
+    DropArea *dropAreaUnderCursor() const;
+
     ///@brief Returns the window being dragged
     WindowBeingDragged *windowBeingDragged() const;
 
@@ -126,7 +129,6 @@ private:
     DragController(QObject * = nullptr);
     StateBase *activeState() const;
     WidgetType *qtTopLevelUnderCursor() const;
-    DropArea *dropAreaUnderCursor() const;
     Draggable *draggableForQObject(QObject *o) const;
     QPoint m_pressPos;
     QPoint m_offset;
diff --git a/src/private/DropIndicatorOverlayInterface.cpp b/src/private/DropIndicatorOverlayInterface.cpp
index ebb9aedb..ee40a8d2 100644
--- a/src/private/DropIndicatorOverlayInterface.cpp
+++ b/src/private/DropIndicatorOverlayInterface.cpp
@@ -161,7 +161,8 @@ bool DropIndicatorOverlayInterface::dropIndicatorVisible(DropLocation dropLoc) c
     }
 
     if (auto dropIndicatorAllowedFunc = Config::self().dropIndicatorAllowedFunc()) {
-        if (!dropIndicatorAllowedFunc(dropLoc, source, target))
+        DropArea *dropArea = DragController::instance()->dropAreaUnderCursor();
+        if (!dropIndicatorAllowedFunc(dropLoc, source, target, dropArea))
             return false;
     }