Set window screen from wl_surface.enter and leave events

Removes the pointer mScreen, which would previously cause a crash if the screen
was removed.

Ensures that QWindow::screen() is correct, except in the cases where:

- The compositor has not yet sent enter and leave events (in which case the
  primary output is returned).
- The compositor is not sending enter and leave events (although this is
  mandatory, some compositors don't do this).
- The application developer has tried to move the window with
  QWindow::setScreen(QScreen *). Since there is no way for a client to ask to
  be moved to a specific monitor in windowed mode, we return the requested
  screen until a new enter or leave event is received.

This will also be useful when implementing/fixing features where the current
screen matters. Examples are QT_AUTO_SCREEN_SCALE_FACTOR and the optional
output parameter to wl_shell_surface.set_fullscreen.

Task-number: QTBUG-62044
Change-Id: Iafde2e278fbc8876e8dafe5b2a4d2482fdc7961a
Reviewed-by: Paul Olav Tvete <paul.tvete@qt.io>

src/plugins/platforms/wayland/qwaylandscreen.cpp

@@ -175,6 +175,12 @@ QWaylandScreen * QWaylandScreen::waylandScreenFromWindow(QWindow *window)
     return static_cast<QWaylandScreen *>(platformScreen);
 }
 
+QWaylandScreen *QWaylandScreen::fromWlOutput(::wl_output *output)
+{
+    auto wlOutput = static_cast<QtWayland::wl_output *>(wl_output_get_user_data(output));
+    return static_cast<QWaylandScreen *>(wlOutput);
+}
+
 void QWaylandScreen::output_mode(uint32_t flags, int width, int height, int refresh)
 {
     if (!(flags & WL_OUTPUT_MODE_CURRENT))

src/plugins/platforms/wayland/qwaylandscreen_p.h

@@ -99,6 +99,7 @@ public:
     ::wl_output *output() { return object(); }
 
     static QWaylandScreen *waylandScreenFromWindow(QWindow *window);
+    static QWaylandScreen *fromWlOutput(::wl_output *output);
 
 private:
     void output_mode(uint32_t flags, int width, int height, int refresh) override;

src/plugins/platforms/wayland/qwaylandwindow.cpp

@@ -69,6 +69,8 @@
 
 #include <QtCore/QDebug>
 
+#include <wayland-client-core.h>
+
 QT_BEGIN_NAMESPACE
 
 namespace QtWaylandClient {
@@ -78,8 +80,7 @@ QWaylandWindow *QWaylandWindow::mMouseGrab = 0;
 QWaylandWindow::QWaylandWindow(QWindow *window)
     : QObject()
     , QPlatformWindow(window)
-    , mScreen(QWaylandScreen::waylandScreenFromWindow(window))
-    , mDisplay(mScreen->display())
+    , mDisplay(screen()->display())
     , mShellSurface(0)
     , mSubSurfaceWindow(0)
     , mWindowDecoration(0)
@@ -99,6 +100,7 @@ QWaylandWindow::QWaylandWindow(QWindow *window)
 {
     static WId id = 1;
     mWindowId = id++;
+    connect(qApp, &QGuiApplication::screenRemoved, this, &QWaylandWindow::handleScreenRemoved);
     initializeWlSurface();
 }
 
@@ -356,6 +358,11 @@ void QWaylandWindow::closePopups(QWaylandWindow *parent)
     }
 }
 
+QWaylandScreen *QWaylandWindow::calculateScreenFromSurfaceEvents() const
+{
+    return mScreens.isEmpty() ? screen() : mScreens.first();
+}
+
 void QWaylandWindow::setVisible(bool visible)
 {
     if (visible) {
@@ -491,6 +498,53 @@ void QWaylandWindow::requestResize()
     QWindowSystemInterface::flushWindowSystemEvents();
 }
 
+void QWaylandWindow::surface_enter(wl_output *output)
+{
+    QWaylandScreen *oldScreen = calculateScreenFromSurfaceEvents();
+    auto addedScreen = QWaylandScreen::fromWlOutput(output);
+
+    if (mScreens.contains(addedScreen)) {
+        qWarning() << "Unexpected wl_surface.enter received for output with id:"
+                   << wl_proxy_get_id(reinterpret_cast<wl_proxy *>(output))
+                   << "screen name:" << addedScreen->name() << "screen model:" << addedScreen->model();
+        return;
+    }
+
+    mScreens.append(addedScreen);
+
+    QWaylandScreen *newScreen = calculateScreenFromSurfaceEvents();
+    if (oldScreen != newScreen) //currently this will only happen if the first wl_surface.enter is for a non-primary screen
+        QWindowSystemInterface::handleWindowScreenChanged(window(), newScreen->QPlatformScreen::screen());
+}
+
+void QWaylandWindow::surface_leave(wl_output *output)
+{
+    QWaylandScreen *oldScreen = calculateScreenFromSurfaceEvents();
+    auto *removedScreen = QWaylandScreen::fromWlOutput(output);
+    bool wasRemoved = mScreens.removeOne(removedScreen);
+    if (!wasRemoved) {
+        qWarning() << "Unexpected wl_surface.leave received for output with id:"
+                   << wl_proxy_get_id(reinterpret_cast<wl_proxy *>(output))
+                   << "screen name:" << removedScreen->name() << "screen model:" << removedScreen->model();
+        return;
+    }
+
+    QWaylandScreen *newScreen = calculateScreenFromSurfaceEvents();
+    if (oldScreen != newScreen)
+        QWindowSystemInterface::handleWindowScreenChanged(window(), newScreen->QPlatformScreen::screen());
+}
+
+void QWaylandWindow::handleScreenRemoved(QScreen *qScreen)
+{
+    QWaylandScreen *oldScreen = calculateScreenFromSurfaceEvents();
+    bool wasRemoved = mScreens.removeOne(static_cast<QWaylandScreen *>(qScreen->handle()));
+    if (wasRemoved) {
+        QWaylandScreen *newScreen = calculateScreenFromSurfaceEvents();
+        if (oldScreen != newScreen)
+            QWindowSystemInterface::handleWindowScreenChanged(window(), newScreen->QPlatformScreen::screen());
+    }
+}
+
 void QWaylandWindow::attach(QWaylandBuffer *buffer, int x, int y)
 {
     if (mFrameCallback) {
@@ -579,6 +633,11 @@ QWaylandSubSurface *QWaylandWindow::subSurfaceWindow() const
     return mSubSurfaceWindow;
 }
 
+QWaylandScreen *QWaylandWindow::screen() const
+{
+    return static_cast<QWaylandScreen *>(QPlatformWindow::screen());
+}
+
 void QWaylandWindow::handleContentOrientationChange(Qt::ScreenOrientation orientation)
 {
     if (mDisplay->compositorVersion() < 2)
@@ -843,7 +902,7 @@ void QWaylandWindow::handleMouseEventWithDecoration(QWaylandInputDevice *inputDe
 #if QT_CONFIG(cursor)
 void QWaylandWindow::setMouseCursor(QWaylandInputDevice *device, const QCursor &cursor)
 {
-    device->setCursor(cursor, mScreen);
+    device->setCursor(cursor, screen());
 }
 
 void QWaylandWindow::restoreMouseCursor(QWaylandInputDevice *device)

src/plugins/platforms/wayland/qwaylandwindow_p.h

@@ -142,7 +142,7 @@ public:
     QWaylandDisplay *display() const { return mDisplay; }
     QWaylandShellSurface *shellSurface() const;
     QWaylandSubSurface *subSurfaceWindow() const;
-    QWaylandScreen *screen() const { return mScreen; }
+    QWaylandScreen *screen() const;
 
     void handleContentOrientationChange(Qt::ScreenOrientation orientation) override;
     void setOrientationMask(Qt::ScreenOrientations mask);
@@ -209,7 +209,10 @@ public slots:
     void requestResize();
 
 protected:
-    QWaylandScreen *mScreen;
+    void surface_enter(struct ::wl_output *output) override;
+    void surface_leave(struct ::wl_output *output) override;
+
+    QVector<QWaylandScreen *> mScreens; //As seen by wl_surface.enter/leave events. Chronological order.
     QWaylandDisplay *mDisplay;
     QWaylandShellSurface *mShellSurface;
     QWaylandSubSurface *mSubSurfaceWindow;
@@ -244,6 +247,9 @@ protected:
 
     QWaylandShmBackingStore *mBackingStore;
 
+private slots:
+    void handleScreenRemoved(QScreen *qScreen);
+
 private:
     bool setWindowStateInternal(Qt::WindowState flags);
     void setGeometry_helper(const QRect &rect);
@@ -254,6 +260,7 @@ private:
     void reset();
     void sendExposeEvent(const QRect &rect);
     static void closePopups(QWaylandWindow *parent);
+    QWaylandScreen *calculateScreenFromSurfaceEvents() const;
 
     void handleMouseEventWithDecoration(QWaylandInputDevice *inputDevice, const QWaylandPointerEvent &e);