Android: Add opt-in high-dpi support

Opt-in by setting android.app.auto_screen_scale_factor
to true in AndroidManifest.xml. This will enable
devicePixelRatio scaling in QtGui using a scale
factor provided by Android DisplayMetrics.

Note that the Android style is not currently supported:
it already accounts for different display densities
which results in incorrect visual sizes when enabling
devicePixelRatio scaling.

Implementation: Bring DisplayMetrics::density through
to setDisplayMetrics in androidjnimain.cpp, similar
to what is done for "scaledDensity". Override
QPlatformScreen::pixelDensity(), which forwards the
scale factor to QtGui.

[The difference between "density" and "scaledDensity"
is that the former is a physical display density factor
which corresponds closely to devicePixelRatio in Qt,
while the latter also includes the Android global font
scale factor.]

Scale the global font pixel size in qandroidplatformtheme.cpp
to keep the visual font size constant.

Based on an initial patch from Daiwei Li <daiweili@suitabletech.com>

Task-number: QTBUG-46615
Change-Id: Ia51f99bf6dda485a57413949246c7b32cb47e8dd
Reviewed-by: BogDan Vatra <bogdan@kdab.com>

2 files changed, 12 insertions, 6 deletions

diff --git a/src/android/jar/src/org/qtproject/qt5/android/QtLayout.java b/src/android/jar/src/org/qtproject/qt5/android/QtLayout.java
index 4d7ca47dde..b11396aeaf 100644
--- a/src/android/jar/src/org/qtproject/qt5/android/QtLayout.java
+++ b/src/android/jar/src/org/qtproject/qt5/android/QtLayout.java
@@ -65,8 +65,8 @@ public class QtLayout extends ViewGroup
     {
         DisplayMetrics metrics = new DisplayMetrics();
         ((Activity) getContext()).getWindowManager().getDefaultDisplay().getMetrics(metrics);
-        QtNative.setApplicationDisplayMetrics(metrics.widthPixels,
-                                              metrics.heightPixels, w, h, metrics.xdpi, metrics.ydpi, metrics.scaledDensity);
+        QtNative.setApplicationDisplayMetrics(metrics.widthPixels, metrics.heightPixels, w, h,
+                                              metrics.xdpi, metrics.ydpi, metrics.scaledDensity, metrics.density);
         if (m_startApplicationRunnable != null) {
             m_startApplicationRunnable.run();
             m_startApplicationRunnable = null;
diff --git a/src/android/jar/src/org/qtproject/qt5/android/QtNative.java b/src/android/jar/src/org/qtproject/qt5/android/QtNative.java
index 07ef6d657d..371e4e4a61 100644
--- a/src/android/jar/src/org/qtproject/qt5/android/QtNative.java
+++ b/src/android/jar/src/org/qtproject/qt5/android/QtNative.java
@@ -77,6 +77,7 @@ public class QtNative
     private static double m_displayMetricsXDpi = .0;
     private static double m_displayMetricsYDpi = .0;
     private static double m_displayMetricsScaledDensity = 1.0;
+    private static double m_displayMetricsDensity = 1.0;
     private static int m_oldx, m_oldy;
     private static final int m_moveThreshold = 0;
     private static ClipboardManager m_clipboardManager = null;
@@ -229,7 +230,8 @@ public class QtNative
                               m_displayMetricsDesktopHeightPixels,
                               m_displayMetricsXDpi,
                               m_displayMetricsYDpi,
-                              m_displayMetricsScaledDensity);
+                              m_displayMetricsScaledDensity,
+                              m_displayMetricsDensity);
             if (params.length() > 0 && !params.startsWith("\t"))
                 params = "\t" + params;
             startQtApplication(f.getAbsolutePath() + params, environment);
@@ -244,7 +246,8 @@ public class QtNative
                                                     int desktopHeightPixels,
                                                     double XDpi,
                                                     double YDpi,
-                                                    double scaledDensity)
+                                                    double scaledDensity,
+                                                    double density)
     {
         /* Fix buggy dpi report */
         if (XDpi < android.util.DisplayMetrics.DENSITY_LOW)
@@ -260,7 +263,8 @@ public class QtNative
                                   desktopHeightPixels,
                                   XDpi,
                                   YDpi,
-                                  scaledDensity);
+                                  scaledDensity,
+                                  density);
             } else {
                 m_displayMetricsScreenWidthPixels = screenWidthPixels;
                 m_displayMetricsScreenHeightPixels = screenHeightPixels;
@@ -269,6 +273,7 @@ public class QtNative
                 m_displayMetricsXDpi = XDpi;
                 m_displayMetricsYDpi = YDpi;
                 m_displayMetricsScaledDensity = scaledDensity;
+                m_displayMetricsDensity = density;
             }
         }
     }
@@ -621,7 +626,8 @@ public class QtNative
                                                 int desktopHeightPixels,
                                                 double XDpi,
                                                 double YDpi,
-                                                double scaledDensity);
+                                                double scaledDensity,
+                                                double density);
     public static native void handleOrientationChanged(int newRotation, int nativeOrientation);
     // screen methods