Add scaling to virtual backend

Reviewers: #plasma

Subscribers: plasma-devel, kwin

Tags: #kwin

Differential Revision: https://phabricator.kde.org/D3497

plugins/platforms/virtual/scene_qpainter_virtual_backend.cpp

@@ -59,7 +59,7 @@ void VirtualQPainterBackend::createOutputs()
 {
     m_backBuffers.clear();
     for (int i = 0; i < screens()->count(); ++i) {
-        QImage buffer(screens()->size(i), QImage::Format_RGB32);
+        QImage buffer(screens()->size(i) * screens()->scale(i), QImage::Format_RGB32);
         buffer.fill(Qt::black);
         m_backBuffers << buffer;
     }