Make rhiFlush() support custom source DPR

The rhiFlush() implementation currently assumes that
QWindow->devicePixelRatio() is the correct scale factor for
transforming device independent window geometry to source geometry.

However, this assumption does not hold if/when we add support
for drawing to a rounded-up DPR, with a downscale later in
the rhiFlush implementation.

Fix this by adding a sourceDevicePixelRatio argument to rhiFlush(),
which is set to either QWindow::devicePixelRatio() or
QWidget::devicePixelRatio(), depending on from where it is used.

Change deviceRect() and friends in qbackingstoredefualtcompositor.cpp
to be scale*() functions instead which take a scale factor instead
of a QWindow. Update call sites to use srouceDevicePixelRatio
where that makes sense.

Pick-to: 6.4
Change-Id: Idb7b1e2f36816a201e00f0defe100d2dc079cb17
Reviewed-by: Eirik Aavitsland <eirik.aavitsland@qt.io>

4 files changed, 6 insertions, 2 deletions

diff --git a/src/plugins/platforms/cocoa/qcocoabackingstore.h b/src/plugins/platforms/cocoa/qcocoabackingstore.h
index ebbf9d1609..6db88f923c 100644
--- a/src/plugins/platforms/cocoa/qcocoabackingstore.h
+++ b/src/plugins/platforms/cocoa/qcocoabackingstore.h
@@ -40,6 +40,7 @@ public:
     void flush(QWindow *, const QRegion &, const QPoint &) override;
 
     FlushResult rhiFlush(QWindow *window,
+                         qreal sourceDevicePixelRatio,
                          const QRegion &region,
                          const QPoint &offset,
                          QPlatformTextureList *textures,
diff --git a/src/plugins/platforms/cocoa/qcocoabackingstore.mm b/src/plugins/platforms/cocoa/qcocoabackingstore.mm
index 21e4d88e73..5d8bd2b7bb 100644
--- a/src/plugins/platforms/cocoa/qcocoabackingstore.mm
+++ b/src/plugins/platforms/cocoa/qcocoabackingstore.mm
@@ -395,6 +395,7 @@ void QCALayerBackingStore::windowDestroyed(QObject *object)
 }
 
 QPlatformBackingStore::FlushResult QCALayerBackingStore::rhiFlush(QWindow *window,
+                                                                  qreal sourceDevicePixelRatio,
                                                                   const QRegion &region,
                                                                   const QPoint &offset,
                                                                   QPlatformTextureList *textures,
@@ -407,7 +408,7 @@ QPlatformBackingStore::FlushResult QCALayerBackingStore::rhiFlush(QWindow *windo
 
     finalizeBackBuffer();
 
-    return QPlatformBackingStore::rhiFlush(window, region, offset, textures, translucentBackground);
+    return QPlatformBackingStore::rhiFlush(window, sourceDevicePixelRatio, region, offset, textures, translucentBackground);
 }
 
 QImage QCALayerBackingStore::toImage() const
diff --git a/src/plugins/platforms/xcb/qxcbbackingstore.cpp b/src/plugins/platforms/xcb/qxcbbackingstore.cpp
index d6cc0bc2af..f3905dff81 100644
--- a/src/plugins/platforms/xcb/qxcbbackingstore.cpp
+++ b/src/plugins/platforms/xcb/qxcbbackingstore.cpp
@@ -866,6 +866,7 @@ void QXcbBackingStore::render(xcb_window_t window, const QRegion &region, const
 }
 
 QPlatformBackingStore::FlushResult QXcbBackingStore::rhiFlush(QWindow *window,
+                                                              qreal sourceDevicePixelRatio,
                                                               const QRegion &region,
                                                               const QPoint &offset,
                                                               QPlatformTextureList *textures,
@@ -876,7 +877,7 @@ QPlatformBackingStore::FlushResult QXcbBackingStore::rhiFlush(QWindow *window,
 
     m_image->flushScrolledRegion(true);
 
-    QPlatformBackingStore::rhiFlush(window, region, offset, textures, translucentBackground);
+    QPlatformBackingStore::rhiFlush(window, sourceDevicePixelRatio, region, offset, textures, translucentBackground);
 
     QXcbWindow *platformWindow = static_cast<QXcbWindow *>(window->handle());
     if (platformWindow->needsSync()) {
diff --git a/src/plugins/platforms/xcb/qxcbbackingstore.h b/src/plugins/platforms/xcb/qxcbbackingstore.h
index c3ee4a9e31..979b254326 100644
--- a/src/plugins/platforms/xcb/qxcbbackingstore.h
+++ b/src/plugins/platforms/xcb/qxcbbackingstore.h
@@ -24,6 +24,7 @@ public:
     QPaintDevice *paintDevice() override;
     void flush(QWindow *window, const QRegion &region, const QPoint &offset) override;
     FlushResult rhiFlush(QWindow *window,
+                         qreal sourceDevicePixelRatio,
                          const QRegion &region,
                          const QPoint &offset,
                          QPlatformTextureList *textures,