Fix off-by-one surface pixel size on Android

m_window->size() may have been rounded for devices
with DPI which results in a fractional DPR (e.g.
650 DPI / 160 DPI = 3.5 DPR). In this case scaling
by devicePixelRatio does not give the correct result.

Instead, use QPlatformWindow geometry and DPR to determine
the device size, without using the (possibly) rounded
device independent window size.

Fixes: QTBUG-87334
Pick-to: 6.6 6.5 6.2
Change-Id: I280236a06516cdb2a1a259fd0cfa8084c1ce7f46
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Jøger Hansegård <joger.hansegard@qt.io>
Reviewed-by: Laszlo Agocs <laszlo.agocs@qt.io>

1 files changed, 7 insertions, 1 deletions

diff --git a/src/gui/rhi/qrhigles2.cpp b/src/gui/rhi/qrhigles2.cpp
index 7148d59d18..fc57cbd072 100644
--- a/src/gui/rhi/qrhigles2.cpp
+++ b/src/gui/rhi/qrhigles2.cpp
@@ -7,6 +7,7 @@
 #include <QtCore/qmap.h>
 #include <QtGui/private/qopenglextensions_p.h>
 #include <QtGui/private/qopenglprogrambinarycache_p.h>
+#include <QtGui/private/qwindow_p.h>
 #include <qpa/qplatformopenglcontext.h>
 #include <qmath.h>
 
@@ -6222,7 +6223,12 @@ QRhiRenderTarget *QGles2SwapChain::currentFrameRenderTarget(StereoTargetBuffer t
 QSize QGles2SwapChain::surfacePixelSize()
 {
     Q_ASSERT(m_window);
-    return m_window->size() * m_window->devicePixelRatio();
+    if (QPlatformWindow *platformWindow = m_window->handle())
+        // Prefer using QPlatformWindow geometry and DPR in order to avoid
+        // errors due to rounded QWindow geometry.
+        return platformWindow->geometry().size() * platformWindow->devicePixelRatio();
+    else
+        return m_window->size() * m_window->devicePixelRatio();
 }
 
 bool QGles2SwapChain::isFormatSupported(Format f)