views: Use scene devicePixelRatio rather than qApp

When possible, use the devicePixelRatio from the scene which on Wayland
unlike the QApplication will properly support fractional scaling.

A KItemViewsUtils class is introduced that can be reused elsewhere.

2 files changed, 43 insertions, 0 deletions

diff --git a/src/kitemviews/private/kitemviewsutils.cpp b/src/kitemviews/private/kitemviewsutils.cpp
new file mode 100644
index 000000000..9e343b6d0
--- /dev/null
+++ b/src/kitemviews/private/kitemviewsutils.cpp
@@ -0,0 +1,23 @@
+/*
+ * SPDX-FileCopyrightText: 2023 Kai Uwe Broulik <[email protected]>
+ *
+ * SPDX-License-Identifier: GPL-2.0-or-later
+ */
+
+#include "kitemviewsutils.h"
+
+#include <QApplication>
+#include <QGraphicsItem>
+#include <QGraphicsScene>
+#include <QGraphicsView>
+
+qreal KItemViewsUtils::devicePixelRatio(const QGraphicsItem *item)
+{
+    qreal dpr = qApp->devicePixelRatio();
+    if (item->scene()) {
+        if (const auto views = item->scene()->views(); !views.isEmpty()) {
+            dpr = views.first()->devicePixelRatioF();
+        }
+    }
+    return dpr;
+}
diff --git a/src/kitemviews/private/kitemviewsutils.h b/src/kitemviews/private/kitemviewsutils.h
new file mode 100644
index 000000000..e9c8bd3e8
--- /dev/null
+++ b/src/kitemviews/private/kitemviewsutils.h
@@ -0,0 +1,20 @@
+/*
+ * SPDX-FileCopyrightText: 2023 Kai Uwe Broulik <[email protected]>
+ *
+ * SPDX-License-Identifier: GPL-2.0-or-later
+ */
+
+#ifndef KITEMVIEWSUTILS_H
+#define KITEMVIEWSUTILS_H
+
+#include <qtypes.h>
+
+class QGraphicsItem;
+
+class KItemViewsUtils
+{
+public:
+    static qreal devicePixelRatio(const QGraphicsItem *item);
+};
+
+#endif // KITEMVIEWSUTILS_H