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, 24 insertions, 12 deletions

diff --git a/src/widgets/kernel/qwidget_p.h b/src/widgets/kernel/qwidget_p.h
index 3e52a6ad2f..08954cc778 100644
--- a/src/widgets/kernel/qwidget_p.h
+++ b/src/widgets/kernel/qwidget_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.
@@ -61,6 +61,7 @@
 #include "QtGui/qinputmethod.h"
 #include "QtGui/qopengl.h"
 #include "QtGui/qsurfaceformat.h"
+#include "QtGui/qscreen.h"
 #include "QtWidgets/qsizepolicy.h"
 #include "QtWidgets/qstyle.h"
 #include "QtWidgets/qapplication.h"
@@ -144,8 +145,7 @@ struct QTLWExtra {
     QRect frameStrut;
     QRect normalGeometry; // used by showMin/maximized/FullScreen
     Qt::WindowFlags savedFlags; // Save widget flags while showing fullscreen
-    // ### TODO replace initialScreenIndex with QScreen *, in case the screens change at runtime
-    int initialScreenIndex; // Screen number when passing a QDesktop[Screen]Widget as parent.
+    QScreen *initialScreen; // Screen when passing a QDesktop[Screen]Widget as parent.
 
 #ifndef QT_NO_OPENGL
     std::vector<std::unique_ptr<QPlatformTextureList>> widgetTextures;
@@ -476,13 +476,11 @@ public:
 
     void setModal_sys();
 
-    // This is an helper function that return the available geometry for
-    // a widget and takes care is this one is in QGraphicsView.
-    // If the widget is not embed in a scene then the geometry available is
-    // null, we let QDesktopWidget decide for us.
-    static QRect screenGeometry(const QWidget *widget)
+    // These helper functions return the (available) geometry for the screen
+    // the widget is on, and takes care if this one is embedded in a QGraphicsView.
+    static QRect graphicsViewParentRect(const QWidget *widget)
     {
-        QRect screen;
+        QRect rect;
 #if QT_CONFIG(graphicsview)
         QGraphicsProxyWidget *ancestorProxy = widget->d_func()->nearestGraphicsProxyWidget(widget);
         //It's embedded if it has an ancestor
@@ -491,16 +489,30 @@ public:
                 // One view, let be smart and return the viewport rect then the popup is aligned
                 if (ancestorProxy->scene()->views().size() == 1) {
                     QGraphicsView *view = ancestorProxy->scene()->views().at(0);
-                    screen = view->mapToScene(view->viewport()->rect()).boundingRect().toRect();
+                    rect = view->mapToScene(view->viewport()->rect()).boundingRect().toRect();
                 } else {
-                    screen = ancestorProxy->scene()->sceneRect().toRect();
+                    rect = ancestorProxy->scene()->sceneRect().toRect();
                 }
             }
         }
 #else
         Q_UNUSED(widget);
 #endif
-        return screen;
+        return rect;
+    }
+    static QRect screenGeometry(const QWidget *widget)
+    {
+        QRect rect = graphicsViewParentRect(widget);
+        if (rect.isNull())
+            rect = widget->screen()->geometry();
+        return rect;
+    }
+    static QRect availableScreenGeometry(const QWidget *widget)
+    {
+        QRect rect = graphicsViewParentRect(widget);
+        if (rect.isNull())
+            rect = widget->screen()->availableGeometry();
+        return rect;
     }
 
     inline void setRedirected(QPaintDevice *replacement, const QPoint &offset)