Subsurface-mobile on Android: change the splash screen methodology

This is based on post by Ben Laud
https://medium.com/@benlaud/complete-guide-to-make-a-splash-screen-for-your-qml-android-application-567ca3bc70af

It creates a theme that uses a splash drawable that Android will show
immediately when the application is launched. And then starts the QML
application with visibility set to false adn only makes it visible (and replace
the splash screen) once initialization is finished.

We still get a little flicker with the switch from splash to start page to dive
list, but over all the experience is hugely improved. And the bug that the
splash screen stays around when starting Subsurface-mobile in landscape also
appears to be fixed.

Fixes #994

Signed-off-by: Dirk Hohndel <dirk@hohndel.org>

android-mobile/AndroidManifest.xml

@@ -14,6 +14,7 @@
             android:name="org.qtproject.qt5.android.bindings.QtActivity"
             android:configChanges="orientation|uiMode|screenLayout|screenSize|smallestScreenSize|locale|fontScale|keyboard|keyboardHidden|navigation"
             android:label="@string/app_name"
+            android:theme="@style/AppTheme"
             android:launchMode="singleTop"
             android:screenOrientation="unspecified" >
             <intent-filter>
@@ -77,7 +78,8 @@
 
 
             <!-- Splash screen -->
-	    <meta-data android:name="android.app.splash_screen_drawable" android:resource="@drawable/subsurface_mobile_splash" />
+<!--	    <meta-data android:name="android.app.splash_screen_drawable" android:resource="@drawable/subsurface_mobile_splash" /> -->
+	    <meta-data android:name="android.app.splash_screen_drawable" android:resource="@drawable/splash" />
             <!-- Splash screen -->
 
         </activity>

android-mobile/res/drawable/splash.xml

@@ -0,0 +1,12 @@
+<?xml version="1.0" encoding="utf-8"?>
+<layer-list xmlns:android="http://schemas.android.com/apk/res/android">
+    <item>
+        <shape android:shape="rectangle" >
+            <solid android:color="#000000FF"/>
+        </shape>
+    </item>
+    <item>
+         <bitmap android:src="@drawable/subsurface_mobile_splash"
+        android:gravity="center" />
+    </item>
+</layer-list>

android-mobile/res/values/apptheme.xml

@@ -0,0 +1,6 @@
+<?xml version="1.0" encoding="utf-8"?>
+<resources>
+    <style name="AppTheme" parent="@android:style/Theme.DeviceDefault.Light.NoActionBar">
+        <item name="android:windowBackground">@drawable/splash</item>
+    </style>
+</resources>

qt-mobile/qml/main.qml

@@ -17,7 +17,8 @@ MobileComponents.ApplicationWindow {
 		id: fontMetrics
 	}
 
-	visible: true
+	visible: false
+	opacity: 0
 
 	globalDrawer: MobileComponents.GlobalDrawer {
 		title: "Subsurface"
@@ -200,6 +201,14 @@ MobileComponents.ApplicationWindow {
 	initialPage: DiveList {
 		anchors.fill: detailsPage
 		id: diveDetails
+		opacity: 0
+		Behavior on opacity {
+			NumberAnimation {
+				duration: 200
+				easing.type: Easing.OutQuad
+			}
+		}
+
 	}
 
 	QMLManager {
@@ -244,5 +253,14 @@ MobileComponents.ApplicationWindow {
 
 	Component.onCompleted: {
 		manager.finishSetup();
+		rootItem.visible = true
+		diveDetails.opacity = 1
+		rootItem.opacity = 1
+	}
+	Behavior on opacity {
+		NumberAnimation {
+			duration: 200
+			easing.type: Easing.OutQuad
+		}
 	}
 }