Replace scale with devicePixelRatio for non-integer scaling

The 'scale' event from wayland cannot support non-integer scaling
which was originally supported in Qt.

As default, devicePixelRatio follows the 'scale' so that the high DPI
still works as the mechanism in Wayland. But if non-integer scaling
factor such as 150% is needed, it can be supported to override the
devicePixelRatio.

Change-Id: I63a04db27bd521264b6d0904e1ddd05a572dc970
Reviewed-by: Elvis Lee <kwangwoong.lee@lge.com>
Reviewed-by: Jungi Byun <jungi.byun@lge.com>
Reviewed-by: Eskil Abrahamsen Blomfeldt <eskil.abrahamsen-blomfeldt@qt.io>

src/plugins/platforms/wayland/qwaylandabstractdecoration.cpp

@@ -122,7 +122,7 @@ const QImage &QWaylandAbstractDecoration::contentImage()
     if (d->m_isDirty) {
         // Update the decoration backingstore
 
-        const int bufferScale = waylandWindow()->scale();
+        const qreal bufferScale = waylandWindow()->scale();
         const QSize imageSize = waylandWindow()->surfaceSize() * bufferScale;
         d->m_decorationContentImage = QImage(imageSize, QImage::Format_ARGB32_Premultiplied);
         // Only scale by buffer scale, not QT_SCALE_FACTOR etc.

src/plugins/platforms/wayland/qwaylandshmbackingstore.cpp

@@ -68,7 +68,7 @@ QT_BEGIN_NAMESPACE
 namespace QtWaylandClient {
 
 QWaylandShmBuffer::QWaylandShmBuffer(QWaylandDisplay *display,
-                     const QSize &size, QImage::Format format, int scale)
+                     const QSize &size, QImage::Format format, qreal scale)
 {
     int stride = size.width() * 4;
     int alloc = stride * size.height();
@@ -108,7 +108,7 @@ QWaylandShmBuffer::QWaylandShmBuffer(QWaylandDisplay *display,
     QWaylandShm* shm = display->shm();
     wl_shm_format wl_format = shm->formatFrom(format);
     mImage = QImage(data, size.width(), size.height(), stride, format);
-    mImage.setDevicePixelRatio(qreal(scale));
+    mImage.setDevicePixelRatio(scale);
 
     mShmPool = wl_shm_create_pool(shm->object(), fd, alloc);
     init(wl_shm_pool_create_buffer(mShmPool,0, size.width(), size.height(),
@@ -271,7 +271,7 @@ QWaylandShmBuffer *QWaylandShmBackingStore::getBuffer(const QSize &size)
 void QWaylandShmBackingStore::resize(const QSize &size)
 {
     QMargins margins = windowDecorationMargins();
-    int scale = waylandWindow()->scale();
+    qreal scale = waylandWindow()->scale();
     QSize sizeWithMargins = (size + QSize(margins.left()+margins.right(),margins.top()+margins.bottom())) * scale;
 
     // We look for a free buffer to draw into. If the buffer is not the last buffer we used,

src/plugins/platforms/wayland/qwaylandshmbackingstore_p.h

@@ -71,7 +71,7 @@ class QWaylandWindow;
 class Q_WAYLAND_CLIENT_EXPORT QWaylandShmBuffer : public QWaylandBuffer {
 public:
     QWaylandShmBuffer(QWaylandDisplay *display,
-           const QSize &size, QImage::Format format, int scale = 1);
+           const QSize &size, QImage::Format format, qreal scale = 1);
     ~QWaylandShmBuffer() override;
     QSize size() const override { return mImage.size(); }
     int scale() const override { return int(mImage.devicePixelRatio()); }

src/plugins/platforms/wayland/qwaylandwindow.cpp

@@ -189,7 +189,7 @@ void QWaylandWindow::initWindow()
     // typically be integer 1 (normal-dpi) or 2 (high-dpi). Call set_buffer_scale()
     // to inform the compositor that high-resolution buffers will be provided.
     if (mSurface->version() >= 3)
-        mSurface->set_buffer_scale(scale());
+        mSurface->set_buffer_scale(mScale);
 
     setWindowFlags(window()->flags());
     QRect geometry = windowGeometry();
@@ -571,9 +571,9 @@ void QWaylandWindow::attachOffset(QWaylandBuffer *buffer)
 
 void QWaylandWindow::damage(const QRect &rect)
 {
-    const int s = scale();
+    const qreal s = scale();
     if (mSurface->version() >= 4)
-        mSurface->damage_buffer(s * rect.x(), s * rect.y(), s * rect.width(), s * rect.height());
+        mSurface->damage_buffer(qFloor(s * rect.x()), qFloor(s * rect.y()), qCeil(s * rect.width()), qCeil(s * rect.height()));
     else
         mSurface->damage(rect.x(), rect.y(), rect.width(), rect.height());
 }
@@ -610,9 +610,9 @@ void QWaylandWindow::commit(QWaylandBuffer *buffer, const QRegion &damage)
 
     attachOffset(buffer);
     if (mSurface->version() >= 4) {
-        const int s = scale();
+        const qreal s = scale();
         for (const QRect &rect: damage)
-            mSurface->damage_buffer(s * rect.x(), s * rect.y(), s * rect.width(), s * rect.height());
+            mSurface->damage_buffer(qFloor(s * rect.x()), qFloor(s * rect.y()), qCeil(s * rect.width()), qCeil(s * rect.height()));
     } else {
         for (const QRect &rect: damage)
             mSurface->damage(rect.x(), rect.y(), rect.width(), rect.height());
@@ -1071,14 +1071,14 @@ bool QWaylandWindow::isActive() const
     return mDisplay->isWindowActivated(this);
 }
 
-int QWaylandWindow::scale() const
+qreal QWaylandWindow::scale() const
 {
-    return mScale;
+    return devicePixelRatio();
 }
 
 qreal QWaylandWindow::devicePixelRatio() const
 {
-    return mScale;
+    return qreal(mScale);
 }
 
 bool QWaylandWindow::setMouseGrabEnabled(bool grab)

src/plugins/platforms/wayland/qwaylandwindow_p.h

@@ -154,7 +154,7 @@ public:
 
     void setMask(const QRegion &region) override;
 
-    int scale() const;
+    qreal scale() const;
     qreal devicePixelRatio() const override;
 
     void requestActivateWindow() override;