From ae584145306a95e331b3ea377805848946b83341 Mon Sep 17 00:00:00 2001
From: Johan Klokkhammer Helsing <johan.helsing@qt.io>
Date: Wed, 16 May 2018 08:59:20 +0200
Subject: [PATCH] Client: Lazy load QWaylandCursor

If nothing is trying to access QWaylandScreen::cursor() leave the platform
cursor uninitialized. This in turn avoids initializing cursor themes, which may
use a significant amount of shared memory depending on the cursor size, number
of screens and screen DPI.

Task-number: QTBUG-67796
Change-Id: Ifd062cb52c4889adcaadeb00bea928b8e84a2182
Reviewed-by: Paul Olav Tvete <paul.tvete@qt.io>
---
 .../platforms/wayland/qwaylanddisplay.cpp     |  1 -
 .../platforms/wayland/qwaylandscreen.cpp      | 27 ++++++++-----------
 .../platforms/wayland/qwaylandscreen_p.h      |  6 ++---
 3 files changed, 13 insertions(+), 21 deletions(-)

diff --git a/src/plugins/platforms/wayland/qwaylanddisplay.cpp b/src/plugins/platforms/wayland/qwaylanddisplay.cpp
index 1c2b47da522..0199e169d73 100644
--- a/src/plugins/platforms/wayland/qwaylanddisplay.cpp
+++ b/src/plugins/platforms/wayland/qwaylanddisplay.cpp
@@ -238,7 +238,6 @@ void QWaylandDisplay::registry_global(uint32_t id, const QString &interface, uin
         mScreens.append(screen);
         // We need to get the output events before creating surfaces
         forceRoundTrip();
-        screen->init();
         mWaylandIntegration->screenAdded(screen);
     } else if (interface == QStringLiteral("wl_compositor")) {
         mCompositorVersion = qMin((int)version, 3);
diff --git a/src/plugins/platforms/wayland/qwaylandscreen.cpp b/src/plugins/platforms/wayland/qwaylandscreen.cpp
index 38d97a91dfb..37fe5f3234b 100644
--- a/src/plugins/platforms/wayland/qwaylandscreen.cpp
+++ b/src/plugins/platforms/wayland/qwaylandscreen.cpp
@@ -60,20 +60,6 @@ QWaylandScreen::QWaylandScreen(QWaylandDisplay *waylandDisplay, int version, uin
 {
 }
 
-QWaylandScreen::~QWaylandScreen()
-{
-#if QT_CONFIG(cursor)
-    delete mWaylandCursor;
-#endif
-}
-
-void QWaylandScreen::init()
-{
-#if QT_CONFIG(cursor)
-    mWaylandCursor = new QWaylandCursor(this);
-#endif
-}
-
 QWaylandDisplay * QWaylandScreen::display() const
 {
     return mWaylandDisplay;
@@ -165,11 +151,20 @@ qreal QWaylandScreen::refreshRate() const
 }
 
 #if QT_CONFIG(cursor)
+
 QPlatformCursor *QWaylandScreen::cursor() const
 {
-    return  mWaylandCursor;
+    return const_cast<QWaylandScreen *>(this)->waylandCursor();
 }
-#endif
+
+QWaylandCursor *QWaylandScreen::waylandCursor()
+{
+    if (!mWaylandCursor)
+        mWaylandCursor.reset(new QWaylandCursor(this));
+    return mWaylandCursor.data();
+}
+
+#endif // QT_CONFIG(cursor)
 
 QWaylandScreen * QWaylandScreen::waylandScreenFromWindow(QWindow *window)
 {
diff --git a/src/plugins/platforms/wayland/qwaylandscreen_p.h b/src/plugins/platforms/wayland/qwaylandscreen_p.h
index 9df55d60340..39b72bc2443 100644
--- a/src/plugins/platforms/wayland/qwaylandscreen_p.h
+++ b/src/plugins/platforms/wayland/qwaylandscreen_p.h
@@ -67,9 +67,7 @@ class Q_WAYLAND_CLIENT_EXPORT QWaylandScreen : public QPlatformScreen, QtWayland
 {
 public:
     QWaylandScreen(QWaylandDisplay *waylandDisplay, int version, uint32_t id);
-    ~QWaylandScreen() override;
 
-    void init();
     QWaylandDisplay *display() const;
 
     QString manufacturer() const override;
@@ -95,7 +93,7 @@ public:
 
 #if QT_CONFIG(cursor)
     QPlatformCursor *cursor() const override;
-    QWaylandCursor *waylandCursor() const { return mWaylandCursor; }
+    QWaylandCursor *waylandCursor();
 #endif
 
     uint32_t outputId() const { return m_outputId; }
@@ -130,7 +128,7 @@ private:
     Qt::ScreenOrientation m_orientation = Qt::PrimaryOrientation;
 
 #if QT_CONFIG(cursor)
-    QWaylandCursor *mWaylandCursor = nullptr;
+    QScopedPointer<QWaylandCursor> mWaylandCursor;
 #endif
 };