From f27489d66cc6d8263130451c26c7e4ae40acc6b4 Mon Sep 17 00:00:00 2001
From: Alexander Volkov <a.volkov@rusbitech.ru>
Date: Wed, 22 Apr 2015 19:28:24 +0300
Subject: Properly get appDpiX, appDpiY and appRootWindow for X screen

X screen is a virtual desktop in Qt terminology. So find the
first QScreen which belongs to the requested virtual desktop
and use it to get the values.

Change-Id: If5c08ff6c3e19e1d49d17ae8e1c54e09ffeb97cf
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@theqtcompany.com>
Reviewed-by: Laszlo Agocs <laszlo.agocs@theqtcompany.com>
---
 src/x11extras/qx11info_x11.cpp | 27 +++++++++++++++++++--------
 1 file changed, 19 insertions(+), 8 deletions(-)

diff --git a/src/x11extras/qx11info_x11.cpp b/src/x11extras/qx11info_x11.cpp
index 8d8f337..2d4c5d2 100644
--- a/src/x11extras/qx11info_x11.cpp
+++ b/src/x11extras/qx11info_x11.cpp
@@ -43,6 +43,7 @@
 
 #include <qpa/qplatformnativeinterface.h>
 #include <qpa/qplatformwindow.h>
+#include <QtPlatformHeaders/qxcbscreenfunctions.h>
 #include <qscreen.h>
 #include <qwindow.h>
 #include <qguiapplication.h>
@@ -50,6 +51,14 @@
 
 QT_BEGIN_NAMESPACE
 
+static QScreen *findScreenForVirtualDesktop(int virtualDesktopNumber)
+{
+    foreach (QScreen *screen, QGuiApplication::screens()) {
+        if (QXcbScreenFunctions::virtualDesktopNumber(screen) == virtualDesktopNumber)
+            return screen;
+    }
+    return Q_NULLPTR;
+}
 
 /*!
     \class QX11Info
@@ -103,11 +112,11 @@ int QX11Info::appDpiX(int screen)
         return qRound(scr->logicalDotsPerInchX());
     }
 
-    QList<QScreen *> screens = QGuiApplication::screens();
-    if (screen >= screens.size())
+    QScreen *scr = findScreenForVirtualDesktop(screen);
+    if (!scr)
         return 0;
 
-    return screens[screen]->logicalDotsPerInchX();
+    return scr->logicalDotsPerInchX();
 }
 
 /*!
@@ -130,11 +139,11 @@ int QX11Info::appDpiY(int screen)
         return qRound(scr->logicalDotsPerInchY());
     }
 
-    QList<QScreen *> screens = QGuiApplication::screens();
-    if (screen > screens.size())
+    QScreen *scr = findScreenForVirtualDesktop(screen);
+    if (!scr)
         return 0;
 
-    return screens[screen]->logicalDotsPerInchY();
+    return scr->logicalDotsPerInchY();
 }
 
 /*!
@@ -151,11 +160,13 @@ unsigned long QX11Info::appRootWindow(int screen)
 {
     if (!qApp)
         return 0;
-    Q_UNUSED(screen);
     QPlatformNativeInterface *native = qApp->platformNativeInterface();
     if (!native)
         return 0;
-    return static_cast<xcb_window_t>(reinterpret_cast<quintptr>(native->nativeResourceForIntegration(QByteArrayLiteral("rootwindow"))));
+    QScreen *scr = screen == -1 ?  QGuiApplication::primaryScreen() : findScreenForVirtualDesktop(screen);
+    if (!scr)
+        return 0;
+    return static_cast<xcb_window_t>(reinterpret_cast<quintptr>(native->nativeResourceForScreen(QByteArrayLiteral("rootwindow"), scr)));
 }
 
 /*!
-- 
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