Deal with unreliable Device Pixel Ratio on mobile platforms.

src/QmlControls/ScreenTools.qml

@@ -54,7 +54,20 @@ Item {
     readonly property real largeFontPointRatio:      1.5
 
     property real realPixelDensity:  QGroundControl.corePlugin.options.devicePixelDensity != 0 ? QGroundControl.corePlugin.options.devicePixelDensity : Screen.pixelDensity
-    property real realPixelRatio:    QGroundControl.corePlugin.options.devicePixelRatio != 0 ? QGroundControl.corePlugin.options.devicePixelRatio   : (isMobile ? 1 : Screen.devicePixelRatio)
+
+    property real realPixelRatio: {
+        //-- If a plugin defines it, just use what it tells us
+        if (QGroundControl.corePlugin.options.devicePixelRatio != 0)
+            return QGroundControl.corePlugin.options.devicePixelRatio
+        //-- Mobile is rather unreliable. They all return 1 for Screen.devicePixelRatio.
+        if(isMobile) {
+            //   Lets assume it's unlikely you have a tablet over 300mm wide
+            if((Screen.width / Screen.pixelDensity * Screen.devicePixelRatio) > 300)
+                return 2
+        }
+        //-- Use whatever the system tells us
+        return Screen.devicePixelRatio
+    }
 
     property bool isAndroid:        ScreenToolsController.isAndroid
     property bool isiOS:            ScreenToolsController.isiOS

src/ui/preferences/DebugWindow.qml

@@ -160,13 +160,13 @@ QGCView {
                 font.family:    ScreenTools.normalFontFamily
             }
             Text {
-                text:   Screen.pixelDensity.toFixed(4)
-                color:  qgcPal.text
+                text:           Screen.pixelDensity.toFixed(4)
+                color:          qgcPal.text
                 font.family:    ScreenTools.normalFontFamily
             }
             Text {
-                text:   qsTr("Font Point Size 13.5")
-                color:  qgcPal.text
+                text:           qsTr("Font Point Size 13.5")
+                color:          qgcPal.text
                 font.pointSize: 13.5
                 font.family:    ScreenTools.normalFontFamily
             }
@@ -218,6 +218,38 @@ QGCView {
                 font.pointSize: 15
                 font.family:    ScreenTools.normalFontFamily
             }
+            Text {
+                text:           qsTr("Computed Screen Height:")
+                color:          qgcPal.text
+                font.family:    ScreenTools.normalFontFamily
+            }
+            Text {
+                text:           (Screen.height / Screen.pixelDensity * Screen.devicePixelRatio).toFixed(0)
+                color:          qgcPal.text
+                font.family:    ScreenTools.normalFontFamily
+            }
+            Text {
+                text:           qsTr("Font Point Size 15.5")
+                color:          qgcPal.text
+                font.pointSize: 15.5
+                font.family:    ScreenTools.normalFontFamily
+            }
+            Text {
+                text:           qsTr("Computed Screen Width:")
+                color:          qgcPal.text
+                font.family:    ScreenTools.normalFontFamily
+            }
+            Text {
+                text:           (Screen.width / Screen.pixelDensity * Screen.devicePixelRatio).toFixed(0)
+                color:          qgcPal.text
+                font.family:    ScreenTools.normalFontFamily
+            }
+            Text {
+                text:           qsTr("Font Point Size 16")
+                color:          qgcPal.text
+                font.pointSize: 16
+                font.family:    ScreenTools.normalFontFamily
+            }
         }
 
         Rectangle {