Show high DPI custom cursor on macOS

Set the devicePixelRatio to 1 on the scaled down pixmap.
A scaled down version of the high DPI pixmap is added to the NSCursor in
addition to the high DPI one, but the devicePixelRatio must be set
correctly on the smaller of the two for macOS to pick the right image
to use on a high resolution display (retina).

This change also fixes the problem that only a high DPI custom cursor
with a hotspot in the upper left quadrant is applied by macOS. I suspect
that the NSCursor was discarded by macOS, because the hotspot was
outside the device independent bounds of the smaller scaled image.

Task-number: QTBUG-52211
Change-Id: I7e552e8f62f5255dd3786da44b2f619f6790c37a
Reviewed-by: Morten Johan Sørvig <morten.sorvig@qt.io>

1 files changed, 1 insertions, 0 deletions

diff --git a/src/plugins/platforms/cocoa/qcocoacursor.mm b/src/plugins/platforms/cocoa/qcocoacursor.mm
index c021128e4c..8c98dc69f7 100644
--- a/src/plugins/platforms/cocoa/qcocoacursor.mm
+++ b/src/plugins/platforms/cocoa/qcocoacursor.mm
@@ -314,6 +314,7 @@ NSCursor *QCocoaCursor::createCursorFromPixmap(const QPixmap pixmap, const QPoin
     if (pixmap.devicePixelRatio() > 1.0) {
         QSize layoutSize = pixmap.size() / pixmap.devicePixelRatio();
         QPixmap scaledPixmap = pixmap.scaled(layoutSize, Qt::IgnoreAspectRatio, Qt::SmoothTransformation);
+        scaledPixmap.setDevicePixelRatio(1.0);
         nsimage = static_cast<NSImage *>(qt_mac_create_nsimage(scaledPixmap));
         CGImageRef cgImage = qt_mac_toCGImage(pixmap.toImage());
         NSBitmapImageRep *imageRep = [[NSBitmapImageRep alloc] initWithCGImage:cgImage];