Turn off font hinting when we do high DPI scaling

Font hinting depends on the specific pixel size, and ends up very
wrong when the painter is scaled.

Change-Id: I2007ec7e7ad8d52358d76e88e030ea4df7e91455
Task-number: QTBUG-43809
Reviewed-by: Eskil Abrahamsen Blomfeldt <eskil.abrahamsen-blomfeldt@theqtcompany.com>

5 files changed, 21 insertions, 2 deletions

diff --git a/src/platformsupport/fontdatabases/fontconfig/qfontconfigdatabase.cpp b/src/platformsupport/fontdatabases/fontconfig/qfontconfigdatabase.cpp
index 5dec1d0915..27ff33be86 100644
--- a/src/platformsupport/fontdatabases/fontconfig/qfontconfigdatabase.cpp
+++ b/src/platformsupport/fontdatabases/fontconfig/qfontconfigdatabase.cpp
@@ -521,6 +521,11 @@ QFontEngine::HintStyle defaultHintStyleFromMatch(QFont::HintingPreference hintin
         break;
     }
 
+    if (QGuiApplication::platformNativeInterface()->nativeResourceForScreen("nofonthinting",
+                         QGuiApplication::primaryScreen())) {
+        return QFontEngine::HintNone;
+    }
+
     if (useXftConf) {
         void *hintStyleResource =
                 QGuiApplication::platformNativeInterface()->nativeResourceForScreen("hintstyle",
diff --git a/src/plugins/platforms/xcb/qxcbnativeinterface.cpp b/src/plugins/platforms/xcb/qxcbnativeinterface.cpp
index 3058b29f2d..31dedd40a2 100644
--- a/src/plugins/platforms/xcb/qxcbnativeinterface.cpp
+++ b/src/plugins/platforms/xcb/qxcbnativeinterface.cpp
@@ -78,7 +78,8 @@ static int resourceType(const QByteArray &key)
         QByteArrayLiteral("startupid"), QByteArrayLiteral("traywindow"),
         QByteArrayLiteral("gettimestamp"), QByteArrayLiteral("x11screen"),
         QByteArrayLiteral("rootwindow"),
-        QByteArrayLiteral("subpixeltype"), QByteArrayLiteral("antialiasingEnabled")
+        QByteArrayLiteral("subpixeltype"), QByteArrayLiteral("antialiasingEnabled"),
+        QByteArrayLiteral("nofonthinting")
     };
     const QByteArray *end = names + sizeof(names) / sizeof(names[0]);
     const QByteArray *result = std::find(names, end, key);
@@ -283,6 +284,9 @@ void *QXcbNativeInterface::nativeResourceForScreen(const QByteArray &resource, Q
     case GetTimestamp:
         result = getTimestamp(xcbScreen);
         break;
+    case NoFontHinting:
+        result = xcbScreen->noFontHinting() ? this : 0; //qboolptr...
+        break;
     default:
         break;
     }
diff --git a/src/plugins/platforms/xcb/qxcbnativeinterface.h b/src/plugins/platforms/xcb/qxcbnativeinterface.h
index b667f1a372..330dd008c4 100644
--- a/src/plugins/platforms/xcb/qxcbnativeinterface.h
+++ b/src/plugins/platforms/xcb/qxcbnativeinterface.h
@@ -67,7 +67,8 @@ public:
         X11Screen,
         RootWindow,
         ScreenSubpixelType,
-        ScreenAntialiasingEnabled
+        ScreenAntialiasingEnabled,
+        NoFontHinting
     };
 
     QXcbNativeInterface();
diff --git a/src/plugins/platforms/xcb/qxcbscreen.cpp b/src/plugins/platforms/xcb/qxcbscreen.cpp
index 6559a0bdba..7136455754 100644
--- a/src/plugins/platforms/xcb/qxcbscreen.cpp
+++ b/src/plugins/platforms/xcb/qxcbscreen.cpp
@@ -62,6 +62,7 @@ QXcbScreen::QXcbScreen(QXcbConnection *connection, xcb_screen_t *scr,
     , m_forcedDpi(-1)
     , m_devicePixelRatio(1)
     , m_hintStyle(QFontEngine::HintStyle(-1))
+    , m_noFontHinting(false)
     , m_subpixelType(QFontEngine::SubpixelAntialiasingType(-1))
     , m_antialiasingEnabled(-1)
     , m_xSettings(0)
@@ -86,6 +87,12 @@ QXcbScreen::QXcbScreen(QXcbConnection *connection, xcb_screen_t *scr,
 
     readXResources();
 
+    // disable font hinting when we do UI scaling
+    static bool dpr_scaling_enabled = (qgetenv("QT_DEVICE_PIXEL_RATIO").toInt() > 1
+                           || qgetenv("QT_DEVICE_PIXEL_RATIO").toLower() == "auto");
+    if (dpr_scaling_enabled)
+        m_noFontHinting = true;
+
 #ifdef Q_XCB_DEBUG
     qDebug();
     qDebug("Screen output %s of xcb screen %d:", m_outputName.toUtf8().constData(), m_number);
diff --git a/src/plugins/platforms/xcb/qxcbscreen.h b/src/plugins/platforms/xcb/qxcbscreen.h
index 4675b12d9c..e9ab2edaa0 100644
--- a/src/plugins/platforms/xcb/qxcbscreen.h
+++ b/src/plugins/platforms/xcb/qxcbscreen.h
@@ -98,6 +98,7 @@ public:
     void readXResources();
 
     QFontEngine::HintStyle hintStyle() const { return m_hintStyle; }
+    bool noFontHinting() const { return m_noFontHinting; }
     QFontEngine::SubpixelAntialiasingType subpixelType() const { return m_subpixelType; }
     int antialiasingEnabled() const { return m_antialiasingEnabled; }
 
@@ -132,6 +133,7 @@ private:
     int m_forcedDpi;
     int m_devicePixelRatio;
     QFontEngine::HintStyle m_hintStyle;
+    bool m_noFontHinting;
     QFontEngine::SubpixelAntialiasingType m_subpixelType;
     int m_antialiasingEnabled;
     QXcbXSettings *m_xSettings;