QScreen::grabWindow(): Scale the coordinates.

The coordinates need to be scaled before calling QPlatformScreen::grabWindow()
On return, set a devicePixelRatio on the pixmap.

Adapt the QWidget test to scale the grabbed pixmaps.

Fixes pixeltool displaying the wrong part of the screen when High DPI scaling
is in effect.

Task-number: QTBUG-46615
Change-Id: I12de7df0da669230cf0fae74f4a42d43f061d5ff
Reviewed-by: Morten Johan Sørvig <morten.sorvig@theqtcompany.com>

2 files changed, 18 insertions, 3 deletions

diff --git a/src/gui/kernel/qscreen.cpp b/src/gui/kernel/qscreen.cpp
index 52e7686439..e87f58d735 100644
--- a/src/gui/kernel/qscreen.cpp
+++ b/src/gui/kernel/qscreen.cpp
@@ -40,6 +40,7 @@
 
 #include <QtCore/QDebug>
 #include <QtCore/private/qobject_p.h>
+#include "qhighdpiscaling_p.h"
 
 QT_BEGIN_NAMESPACE
 
@@ -683,7 +684,19 @@ QPixmap QScreen::grabWindow(WId window, int x, int y, int width, int height)
         qWarning("invoked with handle==0");
         return QPixmap();
     }
-    return platformScreen->grabWindow(window, x, y, width, height);
+    const qreal factor = QHighDpiScaling::factor(this);
+    if (qFuzzyCompare(factor, 1))
+        return platformScreen->grabWindow(window, x, y, width, height);
+
+    const QPoint nativePos = QHighDpi::toNative(QPoint(x, y), factor);
+    QSize nativeSize(width, height);
+    if (nativeSize.isValid())
+        nativeSize = QHighDpi::toNative(nativeSize, factor);
+    QPixmap result =
+        platformScreen->grabWindow(window, nativePos.x(), nativePos.y(),
+                                   nativeSize.width(), nativeSize.height());
+    result.setDevicePixelRatio(factor);
+    return result;
 }
 
 #ifndef QT_NO_DEBUG_STREAM
diff --git a/tests/auto/widgets/kernel/qwidget/tst_qwidget.cpp b/tests/auto/widgets/kernel/qwidget/tst_qwidget.cpp
index 8a5250aad4..293689bff3 100644
--- a/tests/auto/widgets/kernel/qwidget/tst_qwidget.cpp
+++ b/tests/auto/widgets/kernel/qwidget/tst_qwidget.cpp
@@ -4979,7 +4979,9 @@ static inline QByteArray msgRgbMismatch(unsigned actual, unsigned expected)
 static QPixmap grabWindow(QWindow *window, int x, int y, int width, int height)
 {
     QScreen *screen = window->screen();
-    return screen ? screen->grabWindow(window->winId(), x, y, width, height) : QPixmap();
+    Q_ASSERT(screen);
+    QPixmap result = screen->grabWindow(window->winId(), x, y, width, height);
+    return result.devicePixelRatio() > 1 ? result.scaled(width, height) : result;
 }
 
 #define VERIFY_COLOR(child, region, color) verifyColor(child, region, color, __LINE__)
@@ -8505,7 +8507,7 @@ void tst_QWidget::translucentWidget()
 #ifdef Q_OS_WIN
     QWidget *desktopWidget = QApplication::desktop()->screen(0);
     if (QSysInfo::windowsVersion() >= QSysInfo::WV_VISTA)
-        widgetSnapshot = qApp->primaryScreen()->grabWindow(desktopWidget->winId(), labelPos.x(), labelPos.y(), label.width(), label.height());
+        widgetSnapshot = grabWindow(desktopWidget->windowHandle(), labelPos.x(), labelPos.y(), label.width(), label.height());
     else
 #endif
         widgetSnapshot = label.grab(QRect(QPoint(0, 0), label.size()));