Fix invisible speed-colored track: use step() with hex string literals

Expression.color(Color.parseColor()) inside interpolate() stops was
silently failing to render on device. Replace with Expression.step()
and Expression.literal(hexString) which MapLibre's renderer handles
natively for line-color.

https://claude.ai/code/session_01YUbuZNDAoLea4cf9UGQ9qn

1 files changed, 7 insertions, 11 deletions

diff --git a/android-app/app/src/main/kotlin/org/terst/nav/track/TrackColors.kt b/android-app/app/src/main/kotlin/org/terst/nav/track/TrackColors.kt
index 3bcabb1..145a4dd 100644
--- a/android-app/app/src/main/kotlin/org/terst/nav/track/TrackColors.kt
+++ b/android-app/app/src/main/kotlin/org/terst/nav/track/TrackColors.kt
@@ -1,10 +1,7 @@
 package org.terst.nav.track
 
-import android.graphics.Color
 import org.maplibre.android.style.expressions.Expression
-import org.maplibre.android.style.layers.PropertyFactory
 import org.maplibre.geojson.Feature
-import org.maplibre.geojson.FeatureCollection
 import org.maplibre.geojson.LineString
 import org.maplibre.geojson.Point
 
@@ -21,15 +18,14 @@ fun speedSegments(points: List<TrackPoint>): List<Feature> =
     }
 
 /**
- * MapLibre expression that interpolates line-color from the "speed" feature property.
+ * MapLibre expression that step-interpolates line-color from the "speed" feature property.
  * Scale: 0 kt → blue · 4 kt → cyan · 7 kt → green · 10 kt → amber · 13+ kt → red.
  */
-fun speedColorExpression(): Expression = Expression.interpolate(
-    Expression.linear(),
+fun speedColorExpression(): Expression = Expression.step(
     Expression.get("speed"),
-    Expression.stop(0,  Expression.color(Color.parseColor("#2196F3"))),  // blue
-    Expression.stop(4,  Expression.color(Color.parseColor("#00BCD4"))),  // cyan
-    Expression.stop(7,  Expression.color(Color.parseColor("#4CAF50"))),  // green
-    Expression.stop(10, Expression.color(Color.parseColor("#FFC107"))),  // amber
-    Expression.stop(13, Expression.color(Color.parseColor("#F44336")))   // red
+    Expression.literal("#2196F3"),   // < 4 kt: blue
+    Expression.stop(4,  Expression.literal("#00BCD4")),  // cyan
+    Expression.stop(7,  Expression.literal("#4CAF50")),  // green
+    Expression.stop(10, Expression.literal("#FFC107")),  // amber
+    Expression.stop(13, Expression.literal("#F44336"))   // red
 )