vcl/qt5/QtInstance.cxx |    7 +++++++
 1 file changed, 7 insertions(+)

New commits:
commit eaf9c8ccb68dfdfb1f509c43ed922f18fa6f5e74
Author:     Michael Weghorn <m.wegh...@posteo.de>
AuthorDate: Wed Mar 13 12:27:12 2024 +0100
Commit:     Christian Lohmaier <lohmaier+libreoff...@googlemail.com>
CommitDate: Tue Mar 19 17:59:35 2024 +0100

    tdf#159915 qt: Force Qt::HighDpiScaleFactorRoundingPolicy::Round
    
    For now, force `Qt::HighDpiScaleFactorRoundingPolicy::Round`
    for the HighDPI-scale factor rounding policy [1], which is the default
    for Qt 5, while Qt 6 defaults to 
`Qt::HighDpiScaleFactorRoundingPolicy::PassThrough`
    (see [2]), which resulted in broken rendering (e.g. "Help" -> "About"
    dialog not showing the whole content) when fractional display scaling like 
150 %
    is configured in the KDE Plasma display settings (in contrast to manually 
setting the
    `QT_SCALE_FACTOR=1.5` env variable to apply scaling, which was working
    fine).
    
    Quoting from [3]:
    
    > The two principal options are whether fractional scale factors should be
    > rounded to an integer or not. Keeping the scale factor as-is will make
    > the user interface size match the OS setting exactly, but may cause
    > painting errors, for example with the Windows style.
    
    Manually setting the env variable `QT_SCALE_FACTOR_ROUNDING_POLICY="Round"`
    has the same effect (and can be used with LO versions not yet
    containing this fix).
    
    (There might be a way to adjust the way that scaling happens
    to make other policies work, but for now, just hard-code to
    the policy that is known to work.)
    
    [1] https://doc.qt.io/qt-6/qt.html#HighDpiScaleFactorRoundingPolicy-enum
    [2] https://doc.qt.io/qt-6/highdpi.html#environment-variable-reference
    [3] 
https://doc.qt.io/qt-6/qguiapplication.html#setHighDpiScaleFactorRoundingPolicy
    
    [Note: The libreoffice-7-6 backport needs an extra Qt version check
    as Qt::HighDpiScaleFactorRoundingPolicy requires Qt 5.14 while
    the 7-6 baseline is lower. The master/libreoffice-24-2 baseline already
    ensures Qt 5.15, see also commit afb4c96d271958ced3175dfc2cf8bb9e8b0a9d3b,
    "qt: Drop code for Qt < 5.15".]
    
    Change-Id: I8eb6911d4dd5faf00912b8f15a58e0bdace1995a
    Reviewed-on: https://gerrit.libreoffice.org/c/core/+/164768
    Tested-by: Jenkins
    Reviewed-by: Michael Weghorn <m.wegh...@posteo.de>
    (cherry picked from commit 86abb6fd8a8f680f9fc5ff1db775845c9f4e254b)
    Reviewed-on: https://gerrit.libreoffice.org/c/core/+/164745
    Reviewed-by: Adolfo Jayme Barrientos <fit...@ubuntu.com>
    (cherry picked from commit a64d0da7d09cd27a332060f61a25980131e48a56)
    Reviewed-on: https://gerrit.libreoffice.org/c/core/+/164815
    Reviewed-by: Xisco Fauli <xiscofa...@libreoffice.org>
    Tested-by: Christian Lohmaier <lohmaier+libreoff...@googlemail.com>
    Reviewed-by: Christian Lohmaier <lohmaier+libreoff...@googlemail.com>

diff --git a/vcl/qt5/QtInstance.cxx b/vcl/qt5/QtInstance.cxx
index df3df5d17a74..2675445702de 100644
--- a/vcl/qt5/QtInstance.cxx
+++ b/vcl/qt5/QtInstance.cxx
@@ -708,6 +708,13 @@ std::unique_ptr<QApplication> 
QtInstance::CreateQApplication(int& nArgc, char**
     // for scaled icons in the native menus
     QApplication::setAttribute(Qt::AA_UseHighDpiPixmaps);
 #endif
+#if QT_VERSION >= QT_VERSION_CHECK(5, 14, 0)
+    // force Qt::HighDpiScaleFactorRoundingPolicy::Round, which is the Qt 5 
default
+    // policy and prevents incorrect rendering with the Qt 6 default policy
+    // Qt::HighDpiScaleFactorRoundingPolicy::PassThrough (tdf#159915)
+    QGuiApplication::setHighDpiScaleFactorRoundingPolicy(
+        Qt::HighDpiScaleFactorRoundingPolicy::Round);
+#endif
 
     FreeableCStr session_manager;
     if (getenv("SESSION_MANAGER") != nullptr)

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