Improved logical and physical DPI APIs.

Made physicalSize() return QSizeF instead, to prevent rounding errors.
Added logicalSize() as the base to compute font pixel sizes instead, and
added convenience functions in QScreen to access the logical and
physical sizes and DPI metrics.

Task-number: QTBUG-21736
Task-number: QTBUG-21737
Change-Id: Ic705dc98eb3632617659e65a0c9a552673dc0c65
Reviewed-on: http://codereview.qt-project.org/5888
Reviewed-by: Qt Sanity Bot <qt_sanity_bot@ovi.com>
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@nokia.com>

5 files changed, 114 insertions, 14 deletions

diff --git a/src/gui/kernel/qplatformscreen_qpa.cpp b/src/gui/kernel/qplatformscreen_qpa.cpp
index 1a8e6d8f7c..86dc0bd588 100644
--- a/src/gui/kernel/qplatformscreen_qpa.cpp
+++ b/src/gui/kernel/qplatformscreen_qpa.cpp
@@ -127,20 +127,41 @@ QScreen *QPlatformScreen::screen() const
 
 /*!
     Reimplement this function in subclass to return the physical size of the
-    screen. This function is used by QFont to convert point sizes to pixel
-    sizes.
+    screen. The physical size represents the actual physical dimensions of
+    the display.
 
     The default implementation takes the pixel size of the screen, considers a
     resolution of 100 dots per inch, and returns the calculated physical size.
     A device with a screen that has different resolutions will need to be
     supported by a suitable reimplementation of this function.
+
+    \sa logcalDpi
 */
-QSize QPlatformScreen::physicalSize() const
+QSizeF QPlatformScreen::physicalSize() const
 {
     static const int dpi = 100;
-    int width = geometry().width() / dpi * qreal(25.4) ;
-    int height = geometry().height() / dpi * qreal(25.4) ;
-    return QSize(width,height);
+    return QSizeF(geometry().size()) / dpi * qreal(25.4);
+}
+
+/*!
+    Reimplement this function in subclass to return the logical horizontal
+    and vertical dots per inch metrics of the screen.
+
+    The logical dots per inch metrics are used by QFont to convert point sizes
+    to pixel sizes.
+
+    The default implementation uses the screen pixel size and physical size to
+    compute the metrics.
+
+    \sa physicalSize
+*/
+QDpi QPlatformScreen::logicalDpi() const
+{
+    QSizeF ps = physicalSize();
+    QSize s = geometry().size();
+
+    return QDpi(25.4 * s.width() / ps.width(),
+                25.4 * s.height() / ps.height());
 }
 
 QPlatformScreen * QPlatformScreen::platformScreenForWindow(const QWindow *window)
diff --git a/src/gui/kernel/qplatformscreen_qpa.h b/src/gui/kernel/qplatformscreen_qpa.h
index 7c20fba0ba..6917d5eca5 100644
--- a/src/gui/kernel/qplatformscreen_qpa.h
+++ b/src/gui/kernel/qplatformscreen_qpa.h
@@ -67,6 +67,8 @@ class QPlatformWindow;
 class QScreen;
 class QSurfaceFormat;
 
+typedef QPair<qreal, qreal> QDpi;
+
 class Q_GUI_EXPORT QPlatformScreenPageFlipper : public QObject
 {
     Q_OBJECT
@@ -93,7 +95,9 @@ public:
 
     virtual int depth() const = 0;
     virtual QImage::Format format() const = 0;
-    virtual QSize physicalSize() const;
+
+    virtual QSizeF physicalSize() const;
+    virtual QDpi logicalDpi() const;
 
     virtual QWindow *topLevelAt(const QPoint &point) const;
     virtual QList<QPlatformScreen *> virtualSiblings() const;
diff --git a/src/gui/kernel/qscreen.cpp b/src/gui/kernel/qscreen.cpp
index 96ed2bd410..c2049af1e5 100644
--- a/src/gui/kernel/qscreen.cpp
+++ b/src/gui/kernel/qscreen.cpp
@@ -102,6 +102,75 @@ QSize QScreen::size() const
 }
 
 /*!
+  Gets the number of physical dots or pixels per inch in the horizontal direction.
+
+  This value represents the actual horizontal pixel density on the screen's display.
+  Depending on what information the underlying system provides the value might not be
+  entirely accurate.
+
+  \sa physicalDotsPerInchY()
+*/
+qreal QScreen::physicalDotsPerInchX() const
+{
+    return size().width() / physicalSize().width() * 25.4;
+}
+
+/*!
+  Gets the number of physical dots or pixels per inch in the vertical direction.
+
+  This value represents the actual vertical pixel density on the screen's display.
+  Depending on what information the underlying system provides the value might not be
+  entirely accurate.
+
+  \sa physicalDotsPerInchX()
+*/
+qreal QScreen::physicalDotsPerInchY() const
+{
+    return size().height() / physicalSize().height() * 25.4;
+}
+
+/*!
+  Gets the number of logical dots or pixels per inch in the horizontal direction.
+
+  This value is used to convert font point sizes to pixel sizes.
+
+  \sa logicalDotsPerInchY()
+*/
+qreal QScreen::logicalDotsPerInchX() const
+{
+    Q_D(const QScreen);
+    return d->platformScreen->logicalDpi().first;
+}
+
+/*!
+  Gets the number of logical dots or pixels per inch in the vertical direction.
+
+  This value is used to convert font point sizes to pixel sizes.
+
+  \sa logicalDotsPerInchX()
+*/
+qreal QScreen::logicalDotsPerInchY() const
+{
+    Q_D(const QScreen);
+    return d->platformScreen->logicalDpi().second;
+}
+
+/*!
+  Get the screen's physical size (in millimeters).
+
+  The physical size represents the actual physical dimensions of the
+  screen's display.
+
+  Depending on what information the underlying system provides the value
+  might not be entirely accurate.
+*/
+QSizeF QScreen::physicalSize() const
+{
+    Q_D(const QScreen);
+    return d->platformScreen->physicalSize();
+}
+
+/*!
   Get the screen's available size.
 
   The available size is the size excluding window manager reserved areas
diff --git a/src/gui/kernel/qscreen.h b/src/gui/kernel/qscreen.h
index ea068cd834..72681eb6da 100644
--- a/src/gui/kernel/qscreen.h
+++ b/src/gui/kernel/qscreen.h
@@ -44,6 +44,9 @@
 
 #include <QtCore/QList>
 #include <QtCore/QObject>
+#include <QtCore/QRect>
+#include <QtCore/QSize>
+#include <QtCore/QSizeF>
 
 QT_BEGIN_HEADER
 
@@ -54,7 +57,6 @@ QT_MODULE(Gui)
 class QPlatformScreen;
 class QScreenPrivate;
 class QWindow;
-class QSize;
 class QRect;
 
 class Q_GUI_EXPORT QScreen : public QObject
@@ -72,6 +74,14 @@ public:
     QSize size() const;
     QRect geometry() const;
 
+    QSizeF physicalSize() const;
+
+    qreal physicalDotsPerInchX() const;
+    qreal physicalDotsPerInchY() const;
+
+    qreal logicalDotsPerInchX() const;
+    qreal logicalDotsPerInchY() const;
+
     QSize availableSize() const;
     QRect availableGeometry() const;
 
diff --git a/src/gui/text/qfont.cpp b/src/gui/text/qfont.cpp
index e8308dba06..3d2dfb9c76 100644
--- a/src/gui/text/qfont.cpp
+++ b/src/gui/text/qfont.cpp
@@ -170,9 +170,7 @@ Q_GUI_EXPORT int qt_defaultDpiX()
 #elif defined(Q_WS_QPA)
     QScreen *screen = QGuiApplication::primaryScreen();
     if (screen) {
-        const QSize screenSize = screen->geometry().size();
-        const QSize physicalSize = screen->handle()->physicalSize();
-        dpi = qRound(screenSize.width() / (physicalSize.width() / qreal(25.4)));
+        dpi = qRound(screen->logicalDotsPerInchX());
     } else {
         //PI has not been initialised, or it is being initialised. Give a default dpi
         dpi = 100;
@@ -200,9 +198,7 @@ Q_GUI_EXPORT int qt_defaultDpiY()
 #elif defined(Q_WS_QPA)
     QScreen *screen = QGuiApplication::primaryScreen();
     if (screen) {
-        const QSize screenSize = screen->geometry().size();
-        const QSize physicalSize = screen->handle()->physicalSize();
-        dpi = qRound(screenSize.height() / (physicalSize.height() / qreal(25.4)));
+        dpi = qRound(screen->logicalDotsPerInchY());
     } else {
         //PI has not been initialised, or it is being initialised. Give a default dpi
         dpi = 100;