Load Kwin's internal cursors for the highest resolution of attached monitors

Test Plan:
Hovered over decoration
Looked super crystal clear
Same physical size as when I hover over window contents (which had a buffer scale of 1)

Reviewers: #kwin, graesslin

Reviewed By: #kwin, graesslin

Subscribers: graesslin, kwin

Tags: #kwin

Differential Revision: https://phabricator.kde.org/D13608

pointer_input.cpp

@@ -29,6 +29,7 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #include "wayland_server.h"
 #include "workspace.h"
 #include "decorations/decoratedclient.h"
+#include "screens.h"
 // KDecoration
 #include <KDecoration2/Decoration>
 // KWayland
@@ -1217,7 +1218,12 @@ void CursorImage::loadThemeCursor(const T &shape, QHash<T, Image> &cursors, Imag
         if (!buffer) {
             return;
         }
-        it = decltype(it)(cursors.insert(shape, {buffer->data().copy(), QPoint(cursor->hotspot_x, cursor->hotspot_y)}));
+        auto scale = screens()->maxScale();
+        int hotSpotX = qRound(cursor->hotspot_x / scale);
+        int hotSpotY = qRound(cursor->hotspot_y / scale);
+        QImage img = buffer->data().copy();
+        img.setDevicePixelRatio(scale);
+        it = decltype(it)(cursors.insert(shape, {img, QPoint(hotSpotX, hotSpotY)}));
     }
     image->hotSpot = it.value().hotSpot;
     image->image = it.value().image;

screens.cpp

@@ -56,6 +56,7 @@ Screens::Screens(QObject *parent)
     , m_currentFollowsMouse(false)
     , m_changedTimer(new QTimer(this))
     , m_orientationSensor(new OrientationSensor(this))
+    , m_maxScale(1.0)
 {
     connect(this, &Screens::changed, this,
         [this] {
@@ -105,6 +106,11 @@ float Screens::refreshRate(int screen) const
     return 60.0f;
 }
 
+qreal Screens::maxScale() const
+{
+    return m_maxScale;
+}
+
 qreal Screens::scale(int screen) const
 {
     Q_UNUSED(screen)
@@ -124,13 +130,19 @@ void Screens::reconfigure()
 void Screens::updateSize()
 {
     QRect bounding;
+    qreal maxScale = 1.0;
     for (int i = 0; i < count(); ++i) {
         bounding = bounding.united(geometry(i));
+        maxScale = qMax(maxScale, scale(i));
     }
     if (m_boundingSize != bounding.size()) {
         m_boundingSize = bounding.size();
         emit sizeChanged();
     }
+    if (!qFuzzyCompare(m_maxScale, maxScale)) {
+        m_maxScale = maxScale;
+        emit maxScaleChanged();
+    }
 }
 
 void Screens::setCount(int count)

screens.h

@@ -88,6 +88,14 @@ public:
      **/
     virtual QSize size(int screen) const = 0;
 
+    /**
+     * The highest scale() of all connected screens
+     * for use when deciding what scale to load global assets at
+     * Similar to QGuiApplication::scale
+     * @see scale
+     */
+    qreal maxScale() const;
+
     /*
      * The output scale for this display, for use by high DPI displays
      */
@@ -171,6 +179,11 @@ Q_SIGNALS:
      * @see size()
      **/
     void sizeChanged();
+    /**
+     * Emitted when the maximum scale of all attached screens changes
+     * @see maxScale
+     */
+    void maxScaleChanged();
 
 protected Q_SLOTS:
     void setCount(int count);
@@ -196,6 +209,7 @@ private:
     KSharedConfig::Ptr m_config;
     QSize m_boundingSize;
     OrientationSensor *m_orientationSensor;
+    qreal m_maxScale;
 
     KWIN_SINGLETON(Screens)
 };

wayland_cursor_theme.cpp

@@ -20,6 +20,7 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #include "wayland_cursor_theme.h"
 #include "cursor.h"
 #include "wayland_server.h"
+#include "screens.h"
 // Qt
 #include <QVector>
 // KWayland
@@ -37,6 +38,7 @@ WaylandCursorTheme::WaylandCursorTheme(KWayland::Client::ShmPool *shm, QObject *
     , m_theme(nullptr)
     , m_shm(shm)
 {
+    connect(screens(), &Screens::maxScaleChanged, this, &WaylandCursorTheme::loadTheme);
 }
 
 WaylandCursorTheme::~WaylandCursorTheme()
@@ -56,6 +58,8 @@ void WaylandCursorTheme::loadTheme()
         size = 24;
     }
 
+    size *= screens()->maxScale();
+
     auto theme = wl_cursor_theme_load(c->themeName().toUtf8().constData(),
                                    size, m_shm->shm());
     if (theme) {