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>

1 files changed, 2 insertions, 2 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;