Fix default hinting with dpr scaling on Wayland

When high-dpi scaling is enabled, we default to HintNone
currently, since otherwise text layouts (and widget layouts
and anything depending on text size) will have to be updated
when the window is dragged onto a screen with a different dpr.

The check for whether scaling is enabled was based on
QHighDpiScaling::isActive(), which is technically incorrect
since this does not return whether there is a scale on the
painting, rather whether the coordinate system in Qt matches
the one of the platform.

Now that we support agreeing on fractional scale factors with
the Wayland compositor, this issue has become visible, since
QHighDpiScaling::isActive() will now return false for these
compositors, even for fractional scales. For integer scales,
the issue existed before as well, but the kerning issues are
less noticeable in that case.

Pick-to: 6.6 6.7
Fixes: QTBUG-122910
Change-Id: Ic82b07d57a06a351255619f9227dd60396903ade
Reviewed-by: David Edmundson <davidedmundson@kde.org>
Reviewed-by: Kai Uwe Broulik <kde@privat.broulik.de>

3 files changed, 9 insertions, 7 deletions

diff --git a/src/gui/text/unix/qfontconfigdatabase.cpp b/src/gui/text/unix/qfontconfigdatabase.cpp
index 46e8f5724a..975a583220 100644
--- a/src/gui/text/unix/qfontconfigdatabase.cpp
+++ b/src/gui/text/unix/qfontconfigdatabase.cpp
@@ -16,7 +16,6 @@
 #include <qpa/qplatformservices.h>
 
 #include <QtGui/private/qguiapplication_p.h>
-#include <QtGui/private/qhighdpiscaling_p.h>
 
 #include <QtGui/qguiapplication.h>
 
@@ -547,6 +546,11 @@ static void populateFromPattern(FcPattern *pattern,
 
 }
 
+static bool isDprScaling()
+{
+    return !qFuzzyCompare(qApp->devicePixelRatio(), 1.0);
+}
+
 QFontconfigDatabase::~QFontconfigDatabase()
 {
     FcConfigDestroy(FcConfigGetCurrent());
@@ -651,7 +655,7 @@ QFontEngine::HintStyle defaultHintStyleFromMatch(QFont::HintingPreference hintin
         break;
     }
 
-    if (QHighDpiScaling::isActive())
+    if (isDprScaling())
         return QFontEngine::HintNone;
 
     int hint_style = 0;
@@ -958,7 +962,7 @@ QFont QFontconfigDatabase::defaultFont() const
 void QFontconfigDatabase::setupFontEngine(QFontEngineFT *engine, const QFontDef &fontDef) const
 {
     bool antialias = !(fontDef.styleStrategy & QFont::NoAntialias);
-    bool forcedAntialiasSetting = !antialias || QHighDpiScaling::isActive();
+    bool forcedAntialiasSetting = !antialias || isDprScaling();
 
     const QPlatformServices *services = QGuiApplicationPrivate::platformIntegration()->services();
     bool useXftConf = false;
diff --git a/src/gui/text/windows/qwindowsfontdatabase.cpp b/src/gui/text/windows/qwindowsfontdatabase.cpp
index 7f7dada056..adc06a6c2a 100644
--- a/src/gui/text/windows/qwindowsfontdatabase.cpp
+++ b/src/gui/text/windows/qwindowsfontdatabase.cpp
@@ -10,7 +10,6 @@
 
 #include <QtGui/QFont>
 #include <QtGui/QGuiApplication>
-#include <QtGui/private/qhighdpiscaling_p.h>
 #include <QtGui/private/qtgui-config_p.h>
 
 #include <QtCore/qmath.h>
@@ -57,7 +56,7 @@ static inline bool useDirectWrite(QFont::HintingPreference hintingPreference,
 
     return hintingPreference == QFont::PreferNoHinting
         || hintingPreference == QFont::PreferVerticalHinting
-        || (QHighDpiScaling::isActive() && hintingPreference == QFont::PreferDefaultHinting);
+        || (!qFuzzyCompare(qApp->devicePixelRatio(), 1.0) && hintingPreference == QFont::PreferDefaultHinting);
 }
 #endif // !QT_NO_DIRECTWRITE
 
diff --git a/src/gui/text/windows/qwindowsfontenginedirectwrite.cpp b/src/gui/text/windows/qwindowsfontenginedirectwrite.cpp
index 04a7a44f27..5946dfe59d 100644
--- a/src/gui/text/windows/qwindowsfontenginedirectwrite.cpp
+++ b/src/gui/text/windows/qwindowsfontenginedirectwrite.cpp
@@ -12,7 +12,6 @@
 #include <QtCore/private/qwinregistry_p.h>
 #include <QtGui/private/qguiapplication_p.h>
 #include <qpa/qplatformintegration.h>
-#include <QtGui/private/qhighdpiscaling_p.h>
 #include <QtGui/qpainterpath.h>
 
 #if QT_CONFIG(directwrite3)
@@ -166,7 +165,7 @@ static DWRITE_MEASURING_MODE renderModeToMeasureMode(DWRITE_RENDERING_MODE rende
 static DWRITE_RENDERING_MODE hintingPreferenceToRenderingMode(const QFontDef &fontDef)
 {
     QFont::HintingPreference hintingPreference = QFont::HintingPreference(fontDef.hintingPreference);
-    if (QHighDpiScaling::isActive() && hintingPreference == QFont::PreferDefaultHinting) {
+    if (!qFuzzyCompare(qApp->devicePixelRatio(), 1.0) && hintingPreference == QFont::PreferDefaultHinting) {
         // Microsoft documentation recommends using asymmetric rendering for small fonts
         // at pixel size 16 and less, and symmetric for larger fonts.
         hintingPreference = fontDef.pixelSize > 16.0