Add a placement strategy for transient ShellClients

A transient ShellClient has an offset position to the parent surface.
Use this to position the ShellClient properly.

This fixes the random placement of menus.

abstract_client.cpp

@@ -812,4 +812,14 @@ AbstractClient *AbstractClient::transientFor()
     return m_transientFor;
 }
 
+bool AbstractClient::hasTransientPlacementHint() const
+{
+    return false;
+}
+
+QPoint AbstractClient::transientPlacementHint() const
+{
+    return QPoint();
+}
+
 }

abstract_client.h

@@ -247,6 +247,15 @@ public:
     // TODO: remove boolean trap
     virtual AbstractClient *findModal(bool allow_itself = false) = 0;
     virtual bool isTransient() const;
+    /**
+     * @returns Whether there is a hint available to place the AbstractClient on it's parent, default @c false.
+     * @see transientPlacementHint
+     **/
+    virtual bool hasTransientPlacementHint() const;
+    /**
+     * @returns The recommended position of the transient in parent coordinates
+     **/
+    virtual QPoint transientPlacementHint() const;
     const AbstractClient* transientFor() const;
     AbstractClient* transientFor();
     /**

placement.cpp

@@ -72,6 +72,8 @@ void Placement::place(AbstractClient* c, QRect& area)
         placeOnMainWindow(c, area);   // on mainwindow, if any, otherwise centered
     else if (c->isOnScreenDisplay() || c->isNotification())
         placeOnScreenDisplay(c, area);
+    else if (c->isTransient() && c->hasTransientPlacementHint())
+        placeTransient(c);
     else
         place(c, area, options->placement());
 }
@@ -492,6 +494,12 @@ void Placement::placeOnScreenDisplay(AbstractClient* c, QRect& area)
     c->move(QPoint(x, y));
 }
 
+void Placement::placeTransient(AbstractClient *c)
+{
+    // TODO: apply sanity checks?
+    c->move(c->transientFor()->pos() + c->transientPlacementHint());
+}
+
 void Placement::placeDialog(AbstractClient* c, QRect& area, Policy nextPlacement)
 {
     placeOnMainWindow(c, area, nextPlacement);

placement.h

@@ -92,6 +92,7 @@ private:
     void place(AbstractClient* c, QRect& area, Policy policy, Policy nextPlacement = Unknown);
     void placeUnderMouse(AbstractClient* c, QRect& area, Policy next = Unknown);
     void placeOnMainWindow(AbstractClient* c, QRect& area, Policy next = Unknown);
+    void placeTransient(AbstractClient *c);
     QRect checkArea(const AbstractClient*c, const QRect& area);
 
     //CT needed for cascading+

shell_client.cpp

@@ -726,4 +726,14 @@ void ShellClient::setTransient()
     setTransientFor(waylandServer()->findClient(s.data()));
 }
 
+bool ShellClient::hasTransientPlacementHint() const
+{
+    return isTransient() && transientFor() != nullptr;
+}
+
+QPoint ShellClient::transientPlacementHint() const
+{
+    return m_shellSurface->transientOffset();
+}
+
 }

shell_client.h

@@ -112,6 +112,8 @@ public:
     bool isInitialPositionSet() const;
 
     bool isTransient() const override;
+    bool hasTransientPlacementHint() const override;
+    QPoint transientPlacementHint() const override;
 
 protected:
     void addDamage(const QRegion &damage) override;