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, 1 insertions, 0 deletions

diff --git a/src/plugins/platforms/android/qandroidplatformscreen.h b/src/plugins/platforms/android/qandroidplatformscreen.h
index 403d6036f0..c01dbbc712 100644
--- a/src/plugins/platforms/android/qandroidplatformscreen.h
+++ b/src/plugins/platforms/android/qandroidplatformscreen.h
@@ -96,6 +96,7 @@ protected:
 
 private:
     QDpi logicalDpi() const;
+    qreal pixelDensity()  const;
     Qt::ScreenOrientation orientation() const;
     Qt::ScreenOrientation nativeOrientation() const;
     void surfaceChanged(JNIEnv *env, jobject surface, int w, int h);