feat: add high-contrast theme with accessible message bubbles (#5135)

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

core/domain/src/commonMain/kotlin/org/meshtastic/core/domain/usecase/settings/SetContrastLevelUseCase.kt

@@ -0,0 +1,27 @@
+/*
+ * Copyright (c) 2025-2026 Meshtastic LLC
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+package org.meshtastic.core.domain.usecase.settings
+
+import org.koin.core.annotation.Single
+import org.meshtastic.core.repository.UiPrefs
+
+@Single
+open class SetContrastLevelUseCase constructor(private val uiPrefs: UiPrefs) {
+    operator fun invoke(value: Int) {
+        uiPrefs.setContrastLevel(value)
+    }
+}

core/prefs/src/commonMain/kotlin/org/meshtastic/core/prefs/ui/UiPrefsImpl.kt

@@ -62,6 +62,13 @@ class UiPrefsImpl(
         scope.launch { dataStore.edit { it[KEY_THEME] = value } }
     }
 
+    override val contrastLevel: StateFlow<Int> =
+        dataStore.data.map { it[KEY_CONTRAST_LEVEL] ?: 0 }.stateIn(scope, SharingStarted.Lazily, 0)
+
+    override fun setContrastLevel(value: Int) {
+        scope.launch { dataStore.edit { it[KEY_CONTRAST_LEVEL] = value } }
+    }
+
     override val locale: StateFlow<String> =
         dataStore.data.map { it[KEY_LOCALE] ?: "" }.stateIn(scope, SharingStarted.Eagerly, "")
 
@@ -152,6 +159,7 @@ class UiPrefsImpl(
 
         val KEY_APP_INTRO_COMPLETED = booleanPreferencesKey("app_intro_completed")
         val KEY_THEME = intPreferencesKey("theme")
+        val KEY_CONTRAST_LEVEL = intPreferencesKey("contrast-level")
         val KEY_LOCALE = stringPreferencesKey("locale")
         val KEY_NODE_SORT = intPreferencesKey("node-sort-option")
         val KEY_INCLUDE_UNKNOWN = booleanPreferencesKey("include-unknown")

core/repository/src/commonMain/kotlin/org/meshtastic/core/repository/AppPreferences.kt

@@ -80,6 +80,10 @@ interface UiPrefs {
 
     fun setTheme(value: Int)
 
+    val contrastLevel: StateFlow<Int>
+
+    fun setContrastLevel(value: Int)
+
     val locale: StateFlow<String>
 
     fun setLocale(languageTag: String)

core/resources/src/commonMain/composeResources/values/strings.xml

@@ -278,10 +278,15 @@
     <string name="reset_to_defaults">Reset to defaults</string>
     <string name="apply">Apply</string>
     <string name="theme">Theme</string>
+    <string name="contrast">Contrast</string>
     <string name="theme_light">Light</string>
     <string name="theme_dark">Dark</string>
     <string name="theme_system">System default</string>
     <string name="choose_theme">Choose theme</string>
+    <string name="choose_contrast">Contrast level</string>
+    <string name="contrast_standard">Standard</string>
+    <string name="contrast_medium">Medium</string>
+    <string name="contrast_high">High</string>
     <string name="provide_location_to_mesh">Provide phone location to mesh</string>
     <string name="use_homoglyph_characters_encoding">Compact encoding for Cyrillic</string>
     <plurals name="delete_messages">

core/testing/src/commonMain/kotlin/org/meshtastic/core/testing/FakeAppPreferences.kt

@@ -84,6 +84,12 @@ class FakeUiPrefs : UiPrefs {
         theme.value = value
     }
 
+    override val contrastLevel = MutableStateFlow(0)
+
+    override fun setContrastLevel(value: Int) {
+        contrastLevel.value = value
+    }
+
     override val locale = MutableStateFlow("en")
 
     override fun setLocale(languageTag: String) {

core/ui/src/commonMain/kotlin/org/meshtastic/core/ui/theme/ContrastLevel.kt

@@ -0,0 +1,44 @@
+/*
+ * Copyright (c) 2025-2026 Meshtastic LLC
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+package org.meshtastic.core.ui.theme
+
+import androidx.compose.runtime.staticCompositionLocalOf
+
+/**
+ * Application-wide contrast level for accessibility.
+ *
+ * [STANDARD] keeps the default Material 3 color scheme. [MEDIUM] uses Material 3 medium-contrast color tokens and
+ * increases message bubble opacity. [HIGH] uses Material 3 high-contrast color tokens, forces `onSurface` text in
+ * message bubbles, and replaces translucent node-color fills with opaque theme surfaces plus accent borders.
+ */
+enum class ContrastLevel(val value: Int) {
+    STANDARD(0),
+    MEDIUM(1),
+    HIGH(2),
+    ;
+
+    companion object {
+        fun fromValue(value: Int): ContrastLevel = entries.firstOrNull { it.value == value } ?: STANDARD
+    }
+}
+
+/**
+ * Composition local providing the current [ContrastLevel].
+ *
+ * Read by components that need to adapt their rendering for accessibility (e.g. message bubbles, signal indicators).
+ */
+val LocalContrastLevel = staticCompositionLocalOf { ContrastLevel.STANDARD }

core/ui/src/commonMain/kotlin/org/meshtastic/core/ui/theme/Theme.kt

@@ -14,7 +14,7 @@
  * You should have received a copy of the GNU General Public License
  * along with this program.  If not, see <https://www.gnu.org/licenses/>.
  */
-@file:Suppress("UnusedPrivateProperty")
+@file:Suppress("MatchingDeclarationName")
 
 package org.meshtastic.core.ui.theme
 
@@ -25,6 +25,7 @@ import androidx.compose.material3.MotionScheme.Companion.expressive
 import androidx.compose.material3.darkColorScheme
 import androidx.compose.material3.lightColorScheme
 import androidx.compose.runtime.Composable
+import androidx.compose.runtime.CompositionLocalProvider
 import androidx.compose.runtime.Immutable
 import androidx.compose.ui.graphics.Color
 
@@ -272,19 +273,33 @@ val unspecified_scheme = ColorFamily(Color.Unspecified, Color.Unspecified, Color
 fun AppTheme(
     darkTheme: Boolean = isSystemInDarkTheme(),
     dynamicColor: Boolean = true,
+    contrastLevel: ContrastLevel = ContrastLevel.STANDARD,
     content:
     @Composable()
     () -> Unit,
 ) {
-    val dynamicScheme = if (dynamicColor) dynamicColorScheme(darkTheme) else null
-    val colorScheme = dynamicScheme ?: if (darkTheme) darkScheme else lightScheme
+    val dynamicScheme =
+        if (dynamicColor && contrastLevel == ContrastLevel.STANDARD) {
+            dynamicColorScheme(darkTheme)
+        } else {
+            null
+        }
+    val colorScheme =
+        dynamicScheme
+            ?: when (contrastLevel) {
+                ContrastLevel.MEDIUM -> if (darkTheme) mediumContrastDarkColorScheme else mediumContrastLightColorScheme
+                ContrastLevel.HIGH -> if (darkTheme) highContrastDarkColorScheme else highContrastLightColorScheme
+                else -> if (darkTheme) darkScheme else lightScheme
+            }
 
-    MaterialExpressiveTheme(
-        colorScheme = colorScheme,
-        typography = AppTypography,
-        motionScheme = expressive(),
-        content = content,
-    )
+    CompositionLocalProvider(LocalContrastLevel provides contrastLevel) {
+        MaterialExpressiveTheme(
+            colorScheme = colorScheme,
+            typography = AppTypography,
+            motionScheme = expressive(),
+            content = content,
+        )
+    }
 }
 
 const val MODE_DYNAMIC = 6969420

core/ui/src/commonMain/kotlin/org/meshtastic/core/ui/viewmodel/UIViewModel.kt

@@ -118,6 +118,7 @@ class UIViewModel(
     }
 
     val theme: StateFlow<Int> = uiPrefs.theme
+    val contrastLevel: StateFlow<Int> = uiPrefs.contrastLevel
 
     val firmwareEdition = meshLogRepository.getMyNodeInfo().map { nodeInfo -> nodeInfo?.firmware_edition }