Phase 2 of removing QDesktopWidget

Remove QDestopWidget public header, simplify the implementation that
maintains a Qt::Desktop type QWidget for each QScreen, and turn
QWidget's initial target screen into a QScreen pointer.

QApplication::desktop() now takes an optional QScreen pointer, and
returns a QWidget pointer, so that applications and widgets can get
access to the root widget for a specific screen without having to
resort to private APIs.

QDesktopWidgetPrivate implementations to look up a screen for an index,
widget, or point are now all inline functions that thinly wrap
QGuiApplication::screens/screenAt calls. We should consider adding those
as convenience APIs to QScreen instead.

Note that QWidget::screen is assumed to return a valid pointer; there is
code that handles the case that it returns nullptr (but also code that
trusts that it never is nullptr), so this needs to be defined, verified
with tests, and asserted. We can then simplify the code further.

Change-Id: Ifc89be65a0dce265b6729feaf54121c35137cb94
Reviewed-by: Shawn Rutledge <shawn.rutledge@qt.io>
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>

1 files changed, 70 insertions, 30 deletions

diff --git a/src/widgets/kernel/qdesktopwidget_p.h b/src/widgets/kernel/qdesktopwidget_p.h
index b0ac13808d..d2845af17c 100644
--- a/src/widgets/kernel/qdesktopwidget_p.h
+++ b/src/widgets/kernel/qdesktopwidget_p.h
@@ -1,6 +1,6 @@
 /****************************************************************************
 **
-** Copyright (C) 2016 The Qt Company Ltd.
+** Copyright (C) 2020 The Qt Company Ltd.
 ** Contact: https://www.qt.io/licensing/
 **
 ** This file is part of the QtWidgets module of the Qt Toolkit.
@@ -52,56 +52,96 @@
 #define QDESKTOPWIDGET_P_H
 
 #include <QtWidgets/private/qtwidgetsglobal_p.h>
-#include "QDesktopWidget"
 #include "private/qwidget_p.h"
 
-#include <QtCore/qalgorithms.h>
 #include <QtGui/qscreen.h>
+#include <QtCore/private/qflatmap_p.h>
 
 QT_BEGIN_NAMESPACE
 
-class QDesktopScreenWidget : public QWidget {
+class QDesktopWidgetPrivate;
+
+class Q_WIDGETS_EXPORT QDesktopWidget : public QWidget
+{
     Q_OBJECT
 public:
-    explicit QDesktopScreenWidget(QScreen *screen, const QRect &geometry);
+    QDesktopWidget();
+    ~QDesktopWidget();
 
-    int screenNumber() const;
-    void setScreenGeometry(const QRect &geometry);
-
-    QScreen *assignedScreen() const { return m_screen.data(); }
-    QRect screenGeometry() const { return m_geometry; }
 
 private:
-    // The widget updates its screen and geometry automatically. We need to save them separately
-    // to detect changes, and trigger the appropriate signals.
-    const QPointer<QScreen> m_screen;
-    QRect m_geometry;
-};
+    Q_DISABLE_COPY(QDesktopWidget)
+    Q_DECLARE_PRIVATE(QDesktopWidget)
 
-class QDesktopWidgetPrivate : public QWidgetPrivate {
-    Q_DECLARE_PUBLIC(QDesktopWidget)
+    friend class QApplication;
+    friend class QApplicationPrivate;
+};
 
+class QDesktopScreenWidget : public QWidget {
+    Q_OBJECT
 public:
-    ~QDesktopWidgetPrivate() { qDeleteAll(screens); }
-    void _q_updateScreens();
-    QDesktopScreenWidget *widgetForScreen(QScreen *qScreen) const;
+    explicit QDesktopScreenWidget(QScreen *, const QRect &geometry);
 
-    static int screenNumber(const QWidget *widget = nullptr);
-    static int screenNumber(const QPoint &);
+    QScreen *screen() const;
+};
 
-    static QScreen *screen(int screenNo = -1);
+class QDesktopWidgetPrivate : public QWidgetPrivate {
+    Q_DECLARE_PUBLIC(QDesktopWidget)
 
-    static const QRect screenGeometry(int screen = -1);
-    static const QRect screenGeometry(const QWidget *widget);
-    static const QRect screenGeometry(const QPoint &point)
+public:
+    ~QDesktopWidgetPrivate();
+    void updateScreens();
+    QDesktopScreenWidget *widgetForScreen(QScreen *qScreen) const
+    {
+        return screenWidgets.value(qScreen);
+    }
+
+    static inline int screenNumber(const QWidget *widget = nullptr)
+    {
+        if (!widget)
+            return 0;
+        return QGuiApplication::screens().indexOf(widget->screen());
+    }
+
+    static inline int screenNumber(const QPoint &point)
+    {
+        int screenNo = 0;
+        if (QScreen *screen = QGuiApplication::screenAt(point))
+            screenNo = QGuiApplication::screens().indexOf(screen);
+        return screenNo;
+    }
+
+    static inline QScreen *screen(int screenNo = -1)
+    {
+        const QList<QScreen *> screens = QGuiApplication::screens();
+        if (screenNo == -1)
+            screenNo = 0;
+        if (screenNo < 0 || screenNo >= screens.size())
+            return nullptr;
+        return screens.at(screenNo);
+    }
+
+    static inline QRect screenGeometry(int screenNo = -1)
+    {
+        QRect rect;
+        if (const QScreen *s = screen(screenNo))
+            rect = s->geometry();
+        return rect;
+    }
+    static inline QRect screenGeometry(const QPoint &point)
     { return screenGeometry(screenNumber(point)); }
 
-    static const QRect availableGeometry(int screen = -1);
-    static const QRect availableGeometry(const QWidget *widget);
-    static const QRect availableGeometry(const QPoint &point)
+    static inline QRect availableGeometry(int screenNo = -1)
+    {
+        QRect rect;
+        if (const QScreen *s = screen(screenNo))
+            rect = s->availableGeometry();
+        return rect;
+    }
+    static inline QRect availableGeometry(const QPoint &point)
     { return availableGeometry(screenNumber(point)); }
 
-    QList<QDesktopScreenWidget *> screens;
+    QFlatMap<QScreen*, QDesktopScreenWidget*> screenWidgets;
 };
 
 QT_END_NAMESPACE