client: Wait for the compositor to send a fractional scale

Don't assume it's 1.0 initially.

Change-Id: I443cb40a0f3421e6d7bdeba550cc8fc94c646319
Reviewed-by: David Edmundson <davidedmundson@kde.org>
(cherry picked from commit 1452c8d6ee8fe59763d9d48549fe0fbd2466015c)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

3 files changed, 7 insertions, 18 deletions

diff --git a/src/client/qwaylandfractionalscale.cpp b/src/client/qwaylandfractionalscale.cpp
index 324a0b729..34169670f 100644
--- a/src/client/qwaylandfractionalscale.cpp
+++ b/src/client/qwaylandfractionalscale.cpp
@@ -17,17 +17,12 @@ QWaylandFractionalScale::~QWaylandFractionalScale()
     destroy();
 }
 
-qreal QWaylandFractionalScale::preferredScale() const
-{
-    return mPreferredScale;
-}
-
 void QWaylandFractionalScale::wp_fractional_scale_v1_preferred_scale(uint scale)
 {
     qreal preferredScale = scale / 120.0; // hardcoded denominator determined in the spec
     if (preferredScale != mPreferredScale) {
         mPreferredScale = preferredScale;
-        Q_EMIT preferredScaleChanged();
+        Q_EMIT preferredScaleChanged(preferredScale);
     }
 }
 
diff --git a/src/client/qwaylandfractionalscale_p.h b/src/client/qwaylandfractionalscale_p.h
index 0483eb338..c030e60dd 100644
--- a/src/client/qwaylandfractionalscale_p.h
+++ b/src/client/qwaylandfractionalscale_p.h
@@ -20,6 +20,8 @@
 
 #include <QObject>
 
+#include <optional>
+
 QT_BEGIN_NAMESPACE
 
 namespace QtWaylandClient {
@@ -31,16 +33,14 @@ public:
     explicit QWaylandFractionalScale(struct ::wp_fractional_scale_v1 *object);
     ~QWaylandFractionalScale();
 
-    qreal preferredScale() const;
-
 Q_SIGNALS:
-    void preferredScaleChanged();
+    void preferredScaleChanged(qreal preferredScale);
 
 protected:
     void wp_fractional_scale_v1_preferred_scale(uint scale) override;
 
 private:
-    qreal mPreferredScale = 1.0;
+    std::optional<qreal> mPreferredScale;
 };
 
 }
diff --git a/src/client/qwaylandwindow.cpp b/src/client/qwaylandwindow.cpp
index aea2cfff9..cbf1c2a81 100644
--- a/src/client/qwaylandwindow.cpp
+++ b/src/client/qwaylandwindow.cpp
@@ -105,14 +105,8 @@ void QWaylandWindow::initWindow()
     if (mDisplay->fractionalScaleManager() && qApp->highDpiScaleFactorRoundingPolicy() == Qt::HighDpiScaleFactorRoundingPolicy::PassThrough) {
         mFractionalScale.reset(new QWaylandFractionalScale(mDisplay->fractionalScaleManager()->get_fractional_scale(mSurface->object())));
 
-        qreal preferredScale = std::max(1.0, mFractionalScale->preferredScale());
-        if (mScale != preferredScale) {
-            mScale = preferredScale;
-            QWindowSystemInterface::handleWindowDevicePixelRatioChanged(window());
-        }
-
-        connect(mFractionalScale.data(), &QWaylandFractionalScale::preferredScaleChanged, this, [this]() {
-            qreal preferredScale = std::max(1.0, mFractionalScale->preferredScale());
+        connect(mFractionalScale.data(), &QWaylandFractionalScale::preferredScaleChanged, this, [this](qreal preferredScale) {
+            preferredScale = std::max(1.0, preferredScale);
             if (mScale == preferredScale) {
                 return;
             }