Update Dpi and scale factor computation

Remove pixelScale() in favor of logicalBaseDpi(). Compute scale factor
based on logical DPI and logical base DPI, or optionally based on the
physical DPI.

Add policies for running the scale factor and adjusting the logical
DPI reported to the application. The policies are set via environment
variables:

  QT_SCALE_FACTOR_ROUNDING_POLICY=Round|Ceil|Floor|RoundPreferFloor|PassThrough
  QT_DPI_ADJUSTMENT_POLICY=AdjustDpi|DontAdjustDpi|AdjustUpOnly
  QT_USE_PHYSICAL_DPI=0|1

Done-with: Friedemann Kleint <Friedemann.Kleint@qt.io>
Task-number: QTBUG-53022
Change-Id: I4846f223186df665eb0a9c827eaef0a96d1f458f
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@qt.io>

7 files changed, 9 insertions, 29 deletions

diff --git a/src/plugins/platforms/android/qandroidplatformscreen.cpp b/src/plugins/platforms/android/qandroidplatformscreen.cpp
index 7dc8bb8080..80757c2135 100644
--- a/src/plugins/platforms/android/qandroidplatformscreen.cpp
+++ b/src/plugins/platforms/android/qandroidplatformscreen.cpp
@@ -401,15 +401,17 @@ void QAndroidPlatformScreen::doRedraw()
         m_dirtyRect = QRect();
 }
 
+static const int androidLogicalDpi = 72;
+
 QDpi QAndroidPlatformScreen::logicalDpi() const
 {
-    qreal lDpi = QtAndroid::scaledDensity() * 72;
+    qreal lDpi = QtAndroid::scaledDensity() * androidLogicalDpi;
     return QDpi(lDpi, lDpi);
 }
 
-qreal QAndroidPlatformScreen::pixelDensity() const
+QDpi QAndroidPlatformScreen::logicalBaseDpi() const
 {
-    return QtAndroid::pixelDensity();
+    return QDpi(androidLogicalDpi, androidLogicalDpi);
 }
 
 Qt::ScreenOrientation QAndroidPlatformScreen::orientation() const
diff --git a/src/plugins/platforms/android/qandroidplatformscreen.h b/src/plugins/platforms/android/qandroidplatformscreen.h
index f15aeae3fd..5dc158e351 100644
--- a/src/plugins/platforms/android/qandroidplatformscreen.h
+++ b/src/plugins/platforms/android/qandroidplatformscreen.h
@@ -103,7 +103,7 @@ protected:
 
 private:
     QDpi logicalDpi() const override;
-    qreal pixelDensity()  const override;
+    QDpi logicalBaseDpi() const override;
     Qt::ScreenOrientation orientation() const override;
     Qt::ScreenOrientation nativeOrientation() const override;
     void surfaceChanged(JNIEnv *env, jobject surface, int w, int h) override;
diff --git a/src/plugins/platforms/cocoa/qcocoascreen.h b/src/plugins/platforms/cocoa/qcocoascreen.h
index 491af2fe9c..60243b79be 100644
--- a/src/plugins/platforms/cocoa/qcocoascreen.h
+++ b/src/plugins/platforms/cocoa/qcocoascreen.h
@@ -68,6 +68,7 @@ public:
     qreal devicePixelRatio() const override { return m_devicePixelRatio; }
     QSizeF physicalSize() const override { return m_physicalSize; }
     QDpi logicalDpi() const override { return m_logicalDpi; }
+    QDpi logicalBaseDpi() const override { return m_logicalDpi; }
     qreal refreshRate() const override { return m_refreshRate; }
     QString name() const override { return m_name; }
     QPlatformCursor *cursor() const override { return m_cursor; }
diff --git a/src/plugins/platforms/windows/qwindowsscreen.cpp b/src/plugins/platforms/windows/qwindowsscreen.cpp
index 282c0b107e..8cd09a34eb 100644
--- a/src/plugins/platforms/windows/qwindowsscreen.cpp
+++ b/src/plugins/platforms/windows/qwindowsscreen.cpp
@@ -256,15 +256,6 @@ QWindow *QWindowsScreen::windowAt(const QPoint &screenPoint, unsigned flags)
     return result;
 }
 
-qreal QWindowsScreen::pixelDensity() const
-{
-    // QTBUG-49195: Use logical DPI instead of physical DPI to calculate
-    // the pixel density since it is reflects the Windows UI scaling.
-    // High DPI auto scaling should be disabled when the user chooses
-    // small fonts on a High DPI monitor, resulting in lower logical DPI.
-    return qMax(1, qRound(logicalDpi().first / 96));
-}
-
 /*!
     \brief Determine siblings in a virtual desktop system.
 
diff --git a/src/plugins/platforms/windows/qwindowsscreen.h b/src/plugins/platforms/windows/qwindowsscreen.h
index 0ccebf6d71..2fd56f53cf 100644
--- a/src/plugins/platforms/windows/qwindowsscreen.h
+++ b/src/plugins/platforms/windows/qwindowsscreen.h
@@ -87,7 +87,7 @@ public:
     QImage::Format format() const override { return m_data.format; }
     QSizeF physicalSize() const override { return m_data.physicalSizeMM; }
     QDpi logicalDpi() const override { return m_data.dpi; }
-    qreal pixelDensity() const override;
+    QDpi logicalBaseDpi() const override { return QDpi(96, 96); };
     qreal devicePixelRatio() const override { return 1.0; }
     qreal refreshRate() const override { return m_data.refreshRateHz; }
     QString name() const override { return m_data.name; }
diff --git a/src/plugins/platforms/xcb/qxcbscreen.cpp b/src/plugins/platforms/xcb/qxcbscreen.cpp
index 8c34bd9c91..145f40ce80 100644
--- a/src/plugins/platforms/xcb/qxcbscreen.cpp
+++ b/src/plugins/platforms/xcb/qxcbscreen.cpp
@@ -679,11 +679,6 @@ QDpi QXcbScreen::logicalDpi() const
     return m_virtualDesktop->dpi();
 }
 
-qreal QXcbScreen::pixelDensity() const
-{
-    return m_pixelDensity;
-}
-
 QPlatformCursor *QXcbScreen::cursor() const
 {
     return m_cursor;
@@ -747,14 +742,6 @@ void QXcbScreen::updateGeometry(const QRect &geometry, uint8_t rotation)
     if (m_sizeMillimeters.isEmpty())
         m_sizeMillimeters = sizeInMillimeters(geometry.size(), m_virtualDesktop->dpi());
 
-    qreal dpi = forcedDpi();
-    if (dpi <= 0)
-        dpi = geometry.width() / physicalSize().width() * qreal(25.4);
-
-    // Use 128 as a reference DPI on small screens. This favors "small UI" over "large UI".
-    qreal referenceDpi = physicalSize().width() <= 320 ? 128 : 96;
-
-    m_pixelDensity = qMax(1, qRound(dpi/referenceDpi));
     m_geometry = geometry;
     m_availableGeometry = geometry & m_virtualDesktop->workArea();
     QWindowSystemInterface::handleScreenGeometryChange(QPlatformScreen::screen(), m_geometry, m_availableGeometry);
diff --git a/src/plugins/platforms/xcb/qxcbscreen.h b/src/plugins/platforms/xcb/qxcbscreen.h
index ec3b07bfb7..62931d2500 100644
--- a/src/plugins/platforms/xcb/qxcbscreen.h
+++ b/src/plugins/platforms/xcb/qxcbscreen.h
@@ -161,7 +161,7 @@ public:
     QImage::Format format() const override;
     QSizeF physicalSize() const override { return m_sizeMillimeters; }
     QDpi logicalDpi() const override;
-    qreal pixelDensity() const override;
+    QDpi logicalBaseDpi() const override { return QDpi(96, 96); };
     QPlatformCursor *cursor() const override;
     qreal refreshRate() const override { return m_refreshRate; }
     Qt::ScreenOrientation orientation() const override { return m_orientation; }
@@ -227,7 +227,6 @@ private:
     Qt::ScreenOrientation m_orientation = Qt::PrimaryOrientation;
     QXcbCursor *m_cursor;
     int m_refreshRate = 60;
-    int m_pixelDensity = 1;
     QEdidParser m_edid;
 };