Stop loading screens flashing white against the chosen theme

Two causes. The activity's window was a Light platform theme with no
values-night, so the bare window was white whatever theme was picked. And on
the category and poem screens Load sits outside the Scaffold, so while a page
was loading nothing painted a background and that white window showed through.

The window is now painted from the chosen theme before the first frame, and
kept in step when the theme changes, which a static XML theme could not do for
sepia or OLED. Load paints its own loading and error states too.

Android 12+ draws its splash before any app code runs, so that one can only
follow the system light/dark setting; picking sepia or OLED on a light-mode
phone still shows a light splash for a frame.

Verified on an API 36 emulator under the OLED theme: the loading screen is now
true black with the themed spinner.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

app/src/main/java/com/ganjoor/android/MainActivity.kt

@@ -10,6 +10,7 @@ import androidx.compose.runtime.CompositionLocalProvider
 import androidx.compose.runtime.remember
 import androidx.compose.ui.platform.LocalLayoutDirection
 import androidx.compose.ui.unit.LayoutDirection
+import androidx.core.graphics.drawable.toDrawable
 import com.ganjoor.android.data.Bookmarks
 import com.ganjoor.android.data.Ganjoor
 import com.ganjoor.android.data.LocalBookmarks
@@ -17,6 +18,7 @@ import com.ganjoor.android.ui.GanjoorApp
 import com.ganjoor.android.ui.LocalSettings
 import com.ganjoor.android.ui.Settings
 import com.ganjoor.android.ui.theme.GanjoorTheme
+import com.ganjoor.android.ui.theme.windowBackground
 import java.util.Locale
 
 class MainActivity : ComponentActivity() {
@@ -35,9 +37,19 @@ class MainActivity : ComponentActivity() {
     override fun onCreate(savedInstanceState: Bundle?) {
         super.onCreate(savedInstanceState)
         Ganjoor.init(applicationContext)
+
+        // Before the first frame: otherwise the window keeps the platform's white through
+        // startup and every screen transition, whatever theme is chosen.
+        val settings = Settings(applicationContext)
+        val systemInDark = resources.configuration.uiMode and
+            Configuration.UI_MODE_NIGHT_MASK == Configuration.UI_MODE_NIGHT_YES
+        window.setBackgroundDrawable(
+            windowBackground(settings.value.theme, systemInDark).toDrawable()
+        )
+
         enableEdgeToEdge()
         setContent {
-            val settings = remember { Settings(applicationContext) }
+            val settings = remember { settings }
             val bookmarks = remember { Bookmarks(applicationContext) }
             // The client reads this flag on every request, so keep it in step with the setting.
             Ganjoor.offline = settings.value.offline

app/src/main/java/com/ganjoor/android/ui/Load.kt

@@ -1,5 +1,6 @@
 package com.ganjoor.android.ui
 
+import androidx.compose.foundation.background
 import androidx.compose.foundation.layout.Arrangement
 import androidx.compose.foundation.layout.Box
 import androidx.compose.foundation.layout.Column
@@ -36,12 +37,23 @@ fun <T> Load(key: Any?, block: suspend () -> T, content: @Composable (T) -> Unit
 
     result.let { outcome ->
         when {
-            outcome == null -> Box(Modifier.fillMaxSize(), Alignment.Center) {
+            // Painted explicitly: on the category and poem screens Load sits outside the
+            // Scaffold, so while loading nothing else fills the window and the bare window
+            // background would show through.
+            outcome == null -> Box(
+                modifier = Modifier
+                    .fillMaxSize()
+                    .background(MaterialTheme.colorScheme.background),
+                contentAlignment = Alignment.Center,
+            ) {
                 CircularProgressIndicator()
             }
 
             outcome.isFailure -> Column(
-                modifier = Modifier.fillMaxSize().padding(24.dp),
+                modifier = Modifier
+                    .fillMaxSize()
+                    .background(MaterialTheme.colorScheme.background)
+                    .padding(24.dp),
                 verticalArrangement = Arrangement.Center,
                 horizontalAlignment = Alignment.CenterHorizontally,
             ) {

app/src/main/java/com/ganjoor/android/ui/theme/Theme.kt

@@ -8,7 +8,9 @@ import androidx.compose.material3.lightColorScheme
 import androidx.compose.runtime.Composable
 import androidx.compose.runtime.SideEffect
 import androidx.compose.ui.graphics.Color
+import androidx.compose.ui.graphics.toArgb
 import androidx.compose.ui.platform.LocalView
+import androidx.core.graphics.drawable.toDrawable
 import androidx.core.view.WindowCompat
 import com.ganjoor.android.ui.Language
 import com.ganjoor.android.ui.ThemeMode
@@ -146,6 +148,20 @@ private val SepiaDarkScheme = darkColorScheme(
     outline = Color(0xFF968A72),
 )
 
+/**
+ * The window's own background colour for a theme. The activity paints this before Compose runs,
+ * so the gap between the window appearing and the first frame matches the theme instead of
+ * flashing the platform's white. A static XML theme can't express sepia or OLED, hence this.
+ */
+fun windowBackground(mode: ThemeMode, systemInDark: Boolean): Int = when (mode) {
+    ThemeMode.Light -> LightScheme
+    ThemeMode.Dark -> DarkScheme
+    ThemeMode.Sepia -> SepiaScheme
+    ThemeMode.SepiaDark -> SepiaDarkScheme
+    ThemeMode.Black -> BlackScheme
+    ThemeMode.System -> if (systemInDark) DarkScheme else LightScheme
+}.background.toArgb()
+
 @Composable
 fun GanjoorTheme(mode: ThemeMode, language: Language, content: @Composable () -> Unit) {
     val dark = when (mode) {
@@ -164,6 +180,9 @@ fun GanjoorTheme(mode: ThemeMode, language: Language, content: @Composable () ->
     if (!view.isInEditMode) {
         SideEffect {
             val window = (view.context as Activity).window
+            // Keep the window in step when the theme changes, so switching themes doesn't leave
+            // a stale colour behind transitions.
+            window.setBackgroundDrawable(scheme.background.toArgb().toDrawable())
             WindowCompat.getInsetsController(window, view).apply {
                 isAppearanceLightStatusBars = !dark
                 isAppearanceLightNavigationBars = !dark

app/src/main/res/values-night-v31/themes.xml

@@ -0,0 +1,13 @@
+<?xml version="1.0" encoding="utf-8"?>
+<resources>
+
+    <!--
+      Android 12+ draws its own splash from these attributes, before any of our code runs, so it
+      can only follow the system's light/dark setting — not the theme chosen inside the app.
+      Picking sepia or OLED on a light-mode phone still shows a light splash for one frame.
+    -->
+    <style name="Theme.Ganjoorappandroid" parent="android:Theme.Material.NoActionBar">
+        <item name="android:windowBackground">@color/window_background</item>
+        <item name="android:windowSplashScreenBackground">@color/window_background</item>
+    </style>
+</resources>

app/src/main/res/values-night/colors.xml

@@ -0,0 +1,5 @@
+<?xml version="1.0" encoding="utf-8"?>
+<resources>
+    <!-- Matches DarkScheme.background in Theme.kt. -->
+    <color name="window_background">#191C1C</color>
+</resources>

app/src/main/res/values-night/themes.xml

@@ -0,0 +1,7 @@
+<?xml version="1.0" encoding="utf-8"?>
+<resources>
+
+    <style name="Theme.Ganjoorappandroid" parent="android:Theme.Material.NoActionBar">
+        <item name="android:windowBackground">@color/window_background</item>
+    </style>
+</resources>

app/src/main/res/values-v31/themes.xml

@@ -0,0 +1,13 @@
+<?xml version="1.0" encoding="utf-8"?>
+<resources>
+
+    <!--
+      Android 12+ draws its own splash from these attributes, before any of our code runs, so it
+      can only follow the system's light/dark setting — not the theme chosen inside the app.
+      Picking sepia or OLED on a light-mode phone still shows a light splash for one frame.
+    -->
+    <style name="Theme.Ganjoorappandroid" parent="android:Theme.Material.Light.NoActionBar">
+        <item name="android:windowBackground">@color/window_background</item>
+        <item name="android:windowSplashScreenBackground">@color/window_background</item>
+    </style>
+</resources>

app/src/main/res/values/colors.xml

@@ -1,10 +1,5 @@
 <?xml version="1.0" encoding="utf-8"?>
 <resources>
-    <color name="purple_200">#FFBB86FC</color>
-    <color name="purple_500">#FF6200EE</color>
-    <color name="purple_700">#FF3700B3</color>
-    <color name="teal_200">#FF03DAC5</color>
-    <color name="teal_700">#FF018786</color>
-    <color name="black">#FF000000</color>
-    <color name="white">#FFFFFFFF</color>
+    <!-- Matches LightScheme.background in Theme.kt. -->
+    <color name="window_background">#FAFDFC</color>
 </resources>

app/src/main/res/values/themes.xml

@@ -1,5 +1,12 @@
 <?xml version="1.0" encoding="utf-8"?>
 <resources>
 
-    <style name="Theme.Ganjoorappandroid" parent="android:Theme.Material.Light.NoActionBar" />
+    <!--
+      The starting window Android shows before onCreate runs. MainActivity immediately repaints
+      it from the chosen theme, so this only has to cover light vs dark; values-night supplies
+      the other half.
+    -->
+    <style name="Theme.Ganjoorappandroid" parent="android:Theme.Material.Light.NoActionBar">
+        <item name="android:windowBackground">@color/window_background</item>
+    </style>
 </resources>