car: tint the car UI with the phone's Material You color

Cards over the map use the nav bar's color instead of near-black.

gearslip/src/main/java/app/seb3thehacker/gearslip/car/CarUi.kt

@@ -75,6 +75,7 @@ import androidx.compose.ui.res.vectorResource
 import androidx.compose.ui.text.style.TextOverflow
 import app.seb3thehacker.gearslip.R
 import app.seb3thehacker.gearslip.car.theme.GsColors
+import app.seb3thehacker.gearslip.car.theme.withTintedSurfaces
 import app.seb3thehacker.gearslip.car.theme.GsIconBox
 import app.seb3thehacker.gearslip.car.theme.GsIconButton
 import app.seb3thehacker.gearslip.car.theme.GsButton
@@ -117,7 +118,7 @@ fun CarUi() {
         AppTheme.LIGHT -> false
         AppTheme.DARK -> true
     }
-    val colors = if (dark) dynamicDarkColorScheme(appContext) else dynamicLightColorScheme(appContext)
+    val colors = (if (dark) dynamicDarkColorScheme(appContext) else dynamicLightColorScheme(appContext)).withTintedSurfaces(dark)
     val base = LocalDensity.current
     val insets by CarEnvironment.insets.collectAsState()
     val navigator = remember { CarNavigator(CarSettings.openOnConnect.value) }

gearslip/src/main/java/app/seb3thehacker/gearslip/car/TemplateParts.kt

@@ -106,7 +106,8 @@ internal fun ChromeSurface(
 ) {
     Surface(
         shadowElevation = shadowElevation,
-        color = MaterialTheme.colorScheme.surface,
+        // The nav bar's own container colour, so cards over the map match the rest of the car UI.
+        color = MaterialTheme.colorScheme.surfaceContainer,
         contentColor = MaterialTheme.colorScheme.onSurface,
         shape = shape,
         modifier = modifier,

gearslip/src/main/java/app/seb3thehacker/gearslip/car/theme/CarColors.kt

@@ -0,0 +1,29 @@
+package app.seb3thehacker.gearslip.car.theme
+
+import androidx.compose.material3.ColorScheme
+import androidx.compose.ui.graphics.Color
+import androidx.compose.ui.graphics.compositeOver
+
+/**
+ * The phone's Material You colours, with its accent washed over the surfaces. Material You's own
+ * surfaces are nearly neutral, which reads as flat grey on a car screen; tinting them with the
+ * phone's primary colour (purple on a purple phone) gives the whole UI the phone's hue, the way
+ * Material 3's surface tint does, and it changes with the wallpaper like everything else.
+ * Higher containers take more of the tint, so cards still stand off the background.
+ */
+fun ColorScheme.withTintedSurfaces(dark: Boolean): ColorScheme {
+    val base = if (dark) 0.03f else 0.02f
+    fun tint(own: Color, step: Int) = primary.copy(alpha = base + step * (if (dark) 0.015f else 0.01f)).compositeOver(own)
+    return copy(
+        background = tint(background, 0),
+        surface = tint(surface, 0),
+        surfaceDim = tint(surfaceDim, 0),
+        surfaceContainerLowest = tint(surfaceContainerLowest, 0),
+        surfaceContainerLow = tint(surfaceContainerLow, 1),
+        surfaceContainer = tint(surfaceContainer, 2),
+        surfaceContainerHigh = tint(surfaceContainerHigh, 3),
+        surfaceContainerHighest = tint(surfaceContainerHighest, 4),
+        surfaceBright = tint(surfaceBright, 4),
+        surfaceVariant = tint(surfaceVariant, 3),
+    )
+}