Always outter indicators if the center is obscured with something else

If there's some other floating window over our drop zone, then it's
very difficult to drop if there's no outter indicators.

Now we'll show the outter indicators if we suspect there's some other
window obscuring

src/private/DockRegistry.cpp

@@ -15,6 +15,7 @@
 #include "Position_p.h"
 #include "MultiSplitter_p.h"
 #include "QWidgetAdapter.h"
+#include "Config.h"
 
 #include <QPointer>
 #include <QDebug>
@@ -152,6 +153,38 @@ QStringList DockRegistry::dockWidgetNames() const
     return names;
 }
 
+bool DockRegistry::isProbablyObscured(QWindow *window, FloatingWindow *exclude) const
+{
+    if (!window)
+        return false;
+
+    const QRect geo = window->geometry();
+    for (FloatingWindow *fw : m_nestedWindows) {
+        QWindow *fwWindow = fw->QWidgetAdapter::windowHandle();
+        if (fw == exclude || fwWindow == window)
+            continue;
+
+        if (fwWindow->geometry().intersects(geo)) {
+            // fw might be bellow, but we don't have a way to check. So be conservative and return true.
+            return true;
+        }
+    }
+
+    // Floating windows are Tool (keep above), unless we disabled it in Config
+    const bool targetIsToolWindow = !(Config::self().flags() & Config::Flag_DontUseUtilityFloatingWindows) && floatingWindowForHandle(window) != nullptr;
+
+    for (MainWindowBase *mw : m_mainWindows) {
+        QWindow *mwWindow = mw->window()->windowHandle();
+
+        if (mwWindow != window && !targetIsToolWindow && mwWindow->geometry().intersects(geo)) {
+            // Two main windows that intersect. Return true. If the target is a tool window it will be above, so we don't care.
+            return true;
+        }
+    }
+
+    return false;
+}
+
 MainWindowBase::List DockRegistry::mainWindowsWithAffinity(const QStringList &affinities) const
 {
     MainWindowBase::List result;

src/private/DockRegistry_p.h

@@ -165,6 +165,13 @@ public:
     /// @brief Returns a list of all known dock widget unique names
     QStringList dockWidgetNames() const;
 
+    /// @brief returns if the specified window has some other window on top (with higher Z)
+    /// This is an approximation, as we don't have ways to compare Z, so we mostly intersect
+    /// geometries.
+    /// @param target The window which we want to know if it's probably obscured
+    /// @param exclude This window should not be counted as an obscurer. (It's being dragged).
+    bool isProbablyObscured(QWindow *target, FloatingWindow *exclude) const;
+
 protected:
     bool eventFilter(QObject *watched, QEvent *event) override;
 private:

src/private/DragController.cpp

@@ -337,6 +337,12 @@ void DragController::releaseMouse(QWidgetOrQuick *target)
     }
 }
 
+FloatingWindow *DragController::windowBeingDragged() const
+{
+    return m_windowBeingDragged ? m_windowBeingDragged->floatingWindow()
+                                : nullptr;
+}
+
 static QMouseEvent *mouseEvent(QEvent *e)
 {
     switch (e->type()) {

src/private/DragController_p.h

@@ -50,6 +50,8 @@ public:
     void grabMouseFor(QWidgetOrQuick *);
     void releaseMouse(QWidgetOrQuick *);
 
+    FloatingWindow *windowBeingDragged() const;
+
 Q_SIGNALS:
     void mousePressed();
     void manhattanLengthMove();

src/private/indicators/ClassicIndicators.cpp

@@ -15,6 +15,7 @@
 #include "Frame_p.h"
 #include "Logging_p.h"
 #include "Config.h"
+#include "DockRegistry_p.h"
 #include "FrameworkWidgetFactory.h"
 #include "ClassicIndicatorsWindow_p.h"
 
@@ -86,7 +87,11 @@ void ClassicIndicators::updateIndicatorsVisibility(bool visible)
     const bool isTheOnlyFrame = hoveredFrame && hoveredFrame->isTheOnlyFrame();
 
     m_innerIndicatorsVisible = visible && hoveredFrame;
-    m_outterIndicatorsVisible = visible && !isTheOnlyFrame;
+
+    // If there's only 1 frame in the layout, the outter indicators are redundant, as they do the same thing as the internal ones.
+    // But there might be another window obscuring our target, so it's useful to show the outter indicators in this case
+    m_outterIndicatorsVisible = visible && (!isTheOnlyFrame ||
+                                            DockRegistry::self()->isProbablyObscured(hoveredFrame->window()->windowHandle(), DragController::instance()->windowBeingDragged()));
 
     Q_EMIT innerIndicatorsVisibleChanged();
     Q_EMIT outterIndicatorsVisibleChanged();