fixes

demo-app/src/commonMain/kotlin/dev/sargunv/maplibrecompose/demoapp/app.kt

@@ -157,7 +157,7 @@ fun DemoMapControls(
   if (Platform.supportsBlending) {
     Box(modifier = modifier.fillMaxSize().padding(8.dp)) {
       DisappearingScaleBar(
-        metersPerDp = cameraState.metersPerDpAtTarget,
+        lengthPerDp = cameraState.lengthPerDpAtTarget,
         zoom = cameraState.position.zoom,
         modifier = Modifier.align(Alignment.TopStart),
       )

demo-app/src/commonMain/kotlin/dev/sargunv/maplibrecompose/demoapp/demos/CameraStateDemo.kt

@@ -25,7 +25,7 @@ import dev.sargunv.maplibrecompose.demoapp.DemoOrnamentSettings
 import dev.sargunv.maplibrecompose.demoapp.DemoScaffold
 import dev.sargunv.maplibrecompose.demoapp.format
 import io.github.dellisd.spatialk.geojson.Position
-import kotlin.math.roundToInt
+import io.github.kevincianfarini.alchemist.unit.LengthUnit.International.Meter
 
 private val CHICAGO = Position(latitude = 41.878, longitude = -87.626)
 
@@ -53,14 +53,14 @@ object CameraStateDemo : Demo {
 
         Row(modifier = Modifier.safeDrawingPadding().wrapContentSize(Alignment.Center)) {
           val pos = cameraState.position
-          val scale = cameraState.metersPerDpAtTarget
+          val scale = cameraState.lengthPerDpAtTarget
 
           Cell("Latitude", pos.target.latitude.format(3), Modifier.weight(1.4f))
           Cell("Longitude", pos.target.longitude.format(3), Modifier.weight(1.4f))
           Cell("Zoom", pos.zoom.format(2), Modifier.weight(1f))
           Cell("Bearing", pos.bearing.format(2), Modifier.weight(1f))
           Cell("Tilt", pos.tilt.format(2), Modifier.weight(1f))
-          Cell("Scale", "${scale.roundToInt()}m", Modifier.weight(1f))
+          Cell("Scale", "${scale.toLong(Meter)}m", Modifier.weight(1f))
         }
       }
     }

demo-app/src/commonMain/kotlin/dev/sargunv/maplibrecompose/demoapp/docs/Material3.kt

@@ -33,7 +33,7 @@ fun Material3() {
     )
 
     Box(modifier = Modifier.fillMaxSize().padding(8.dp)) {
-      ScaleBar(cameraState.metersPerDpAtTarget, modifier = Modifier.align(Alignment.TopStart))
+      ScaleBar(cameraState.lengthPerDpAtTarget, modifier = Modifier.align(Alignment.TopStart))
       CompassButton(cameraState, modifier = Modifier.align(Alignment.TopEnd))
       AttributionButton(styleState, modifier = Modifier.align(Alignment.BottomEnd))
     }
@@ -50,7 +50,7 @@ fun Material3() {
 
     Box(modifier = Modifier.fillMaxSize().padding(8.dp)) {
       DisappearingScaleBar(
-        metersPerDp = cameraState.metersPerDpAtTarget,
+        lengthPerDp = cameraState.lengthPerDpAtTarget,
         zoom = cameraState.position.zoom,
         modifier = Modifier.align(Alignment.TopStart),
       ) // (1)!

lib/maplibre-compose-material3/src/commonMain/kotlin/dev/sargunv/maplibrecompose/material3/controls/DisappearingScaleBar.kt

@@ -16,6 +16,7 @@ import androidx.compose.ui.Modifier
 import androidx.compose.ui.graphics.Color
 import androidx.compose.ui.text.TextStyle
 import dev.sargunv.maplibrecompose.material3.defaultScaleBarMeasures
+import io.github.kevincianfarini.alchemist.type.Length
 import kotlin.time.Duration
 import kotlin.time.Duration.Companion.seconds
 import kotlinx.coroutines.delay
@@ -24,9 +25,9 @@ import kotlinx.coroutines.delay
  * An animated scale bar that appears when the [zoom] level of the map changes, and then disappears
  * after [visibilityDuration]. This composable wraps [ScaleBar] with visibility animations.
  *
- * @param metersPerDp how many meters are displayed in one device independent pixel (dp), i.e. the
- *   scale. See
- *   [CameraState.metersPerDpAtTarget][dev.sargunv.maplibrecompose.compose.CameraState.metersPerDpAtTarget]
+ * @param lengthPerDp the real world distance in one device independent pixel (dp), i.e. the scale.
+ *   See
+ *   [CameraState.lengthPerDpAtTarget][dev.sargunv.maplibrecompose.compose.CameraState.lengthPerDpAtTarget]
  * @param zoom zoom level of the map
  * @param modifier the [Modifier] to be applied to this layout node
  * @param measures which measures to show on the scale bar. If `null`, measures will be selected
@@ -42,7 +43,7 @@ import kotlinx.coroutines.delay
  */
 @Composable
 public fun DisappearingScaleBar(
-  metersPerDp: Double,
+  lengthPerDp: Length,
   zoom: Double,
   modifier: Modifier = Modifier,
   measures: ScaleBarMeasures = defaultScaleBarMeasures(),
@@ -71,7 +72,7 @@ public fun DisappearingScaleBar(
     exit = exitTransition,
   ) {
     ScaleBar(
-      metersPerDp = metersPerDp,
+      lengthPerDp = lengthPerDp,
       measures = measures,
       haloColor = haloColor,
       color = color,

lib/maplibre-compose-material3/src/commonMain/kotlin/dev/sargunv/maplibrecompose/material3/controls/ScaleBar.kt

@@ -23,6 +23,10 @@ import androidx.compose.ui.unit.toSize
 import dev.sargunv.maplibrecompose.material3.defaultScaleBarMeasures
 import dev.sargunv.maplibrecompose.material3.drawPathsWithHalo
 import dev.sargunv.maplibrecompose.material3.drawTextWithHalo
+import io.github.kevincianfarini.alchemist.scalar.toLength
+import io.github.kevincianfarini.alchemist.type.Length
+import io.github.kevincianfarini.alchemist.unit.LengthUnit.International.Nanometer
+import kotlin.math.roundToLong
 
 /** Which measures to show on the scale bar. */
 public data class ScaleBarMeasures(
@@ -31,12 +35,12 @@ public data class ScaleBarMeasures(
 )
 
 /**
- * A scale bar composable that shows the current scale of the map in feet, meters or feet and meters
- * when zoomed in to the map, changing to miles and kilometers, respectively, when zooming out.
+ * A scale bar composable that shows the current scale of the map in feet, yards, or meters when
+ * zoomed in to the map, changing to miles and kilometers when zooming out.
  *
- * @param metersPerDp how many meters are displayed in one device independent pixel (dp), i.e. the
- *   scale. See
- *   [CameraState.metersPerDpAtTarget][dev.sargunv.maplibrecompose.compose.CameraState.metersPerDpAtTarget]
+ * @param lengthPerDp the real world distance in one device independent pixel (dp), i.e. the scale.
+ *   See
+ *   [CameraState.lengthPerDpAtTarget][dev.sargunv.maplibrecompose.compose.CameraState.lengthPerDpAtTarget]
  * @param modifier the [Modifier] to be applied to this layout node
  * @param measures which measures to show on the scale bar. If `null`, measures will be selected
  *   based on the system settings or otherwise the user's locale.
@@ -48,7 +52,7 @@ public data class ScaleBarMeasures(
  */
 @Composable
 public fun ScaleBar(
-  metersPerDp: Double,
+  lengthPerDp: Length,
   modifier: Modifier = Modifier,
   measures: ScaleBarMeasures = defaultScaleBarMeasures(),
   haloColor: Color = MaterialTheme.colorScheme.surface,
@@ -83,8 +87,8 @@ public fun ScaleBar(
     // scale bar start/end should not overlap horizontally with canvas bounds
     val maxBarLength = maxWidth - fullStrokeWidth
 
-    val params1 = scaleBarParameters(measures.primary, metersPerDp, maxBarLength)
-    val params2 = measures.secondary?.let { scaleBarParameters(it, metersPerDp, maxBarLength) }
+    val params1 = scaleBarParameters(measures.primary, lengthPerDp, maxBarLength)
+    val params2 = measures.secondary?.let { scaleBarParameters(it, lengthPerDp, maxBarLength) }
 
     Canvas(modifier.fillMaxSize()) {
       val fullStrokeWidthPx = fullStrokeWidth.toPx()
@@ -102,15 +106,15 @@ public fun ScaleBar(
       if (true) { // just want a scope here
         val offsetX =
           alignment.align(
-            size = params1.barLength.toPx().toInt(),
+            size = params1.barWidth.toPx().toInt(),
             space = (size.width - fullStrokeWidthPx).toInt(),
             layoutDirection = layoutDirection,
           )
         paths.add(
           listOf(
             Offset(offsetX + fullStrokeWidthPx / 2f, 0f + textHeightPx / 2f),
             Offset(0f, barEndsHeightPx),
-            Offset(params1.barLength.toPx(), 0f),
+            Offset(params1.barWidth.toPx(), 0f),
             Offset(0f, -barEndsHeightPx),
           )
         )
@@ -127,15 +131,15 @@ public fun ScaleBar(
       if (params2 != null) {
         val offsetX =
           alignment.align(
-            size = params2.barLength.toPx().toInt(),
+            size = params2.barWidth.toPx().toInt(),
             space = (size.width - fullStrokeWidthPx).toInt(),
             layoutDirection = layoutDirection,
           )
         paths.add(
           listOf(
             Offset(offsetX + fullStrokeWidthPx / 2f, y + fullStrokeWidthPx / 2f + barEndsHeightPx),
             Offset(0f, -barEndsHeightPx),
-            Offset(params2.barLength.toPx(), 0f),
+            Offset(params2.barWidth.toPx(), 0f),
             Offset(0f, +barEndsHeightPx),
           )
         )
@@ -178,24 +182,29 @@ public fun ScaleBar(
   }
 }
 
-private data class ScaleBarParams(val barLength: Dp, val text: String)
+private data class ScaleBarParams(val barWidth: Dp, val text: String)
 
 @Composable
 private fun scaleBarParameters(
   measure: ScaleBarMeasure,
-  metersPerDp: Double,
+  lengthPerDp: Length,
   maxBarLength: Dp,
 ): ScaleBarParams {
-  val max = maxBarLength.value * metersPerDp / measure.unitInMeters
+  val max = lengthPerDp * maxBarLength.value.toDouble()
   val stop = findStop(max, measure.stops)
-  return ScaleBarParams((stop * measure.unitInMeters / metersPerDp).dp, measure.getText(stop))
+  return ScaleBarParams(barWidth = (stop / lengthPerDp).dp, text = measure.getText(stop))
 }
 
 /**
  * find the largest stop in the list of stops (sorted in ascending order) that is below or equal
  * [max].
  */
-private fun findStop(max: Double, stops: List<Double>): Double {
+private fun findStop(max: Length, stops: List<Length>): Length {
   val i = stops.binarySearch { it.compareTo(max) }
   return if (i >= 0) stops[i] else stops[(-i - 2).coerceAtLeast(0)]
 }
+
+// https://github.com/kevincianfarini/alchemist/issues/53
+// https://github.com/kevincianfarini/alchemist/issues/54
+private operator fun Length.times(other: Double) =
+  (this.toLong(Nanometer) * other).roundToLong().toLength(Nanometer)

lib/maplibre-compose-material3/src/commonMain/kotlin/dev/sargunv/maplibrecompose/material3/controls/ScaleBarMeasure.kt

@@ -7,21 +7,17 @@ import dev.sargunv.maplibrecompose.material3.generated.kilometers_symbol
 import dev.sargunv.maplibrecompose.material3.generated.meters_symbol
 import dev.sargunv.maplibrecompose.material3.generated.miles_symbol
 import dev.sargunv.maplibrecompose.material3.generated.yards_symbol
-import io.github.kevincianfarini.alchemist.scalar.feet
-import io.github.kevincianfarini.alchemist.scalar.kilometers
-import io.github.kevincianfarini.alchemist.scalar.meters
-import io.github.kevincianfarini.alchemist.scalar.miles
-import io.github.kevincianfarini.alchemist.scalar.nanometers
-import io.github.kevincianfarini.alchemist.scalar.yards
+import io.github.kevincianfarini.alchemist.scalar.toLength
 import io.github.kevincianfarini.alchemist.type.Length
 import io.github.kevincianfarini.alchemist.unit.LengthUnit
 import io.github.kevincianfarini.alchemist.unit.LengthUnit.International.Kilometer
 import io.github.kevincianfarini.alchemist.unit.LengthUnit.International.Meter
+import io.github.kevincianfarini.alchemist.unit.LengthUnit.International.Nanometer
 import io.github.kevincianfarini.alchemist.unit.LengthUnit.UnitedStatesCustomary.Foot
 import io.github.kevincianfarini.alchemist.unit.LengthUnit.UnitedStatesCustomary.Mile
 import io.github.kevincianfarini.alchemist.unit.LengthUnit.UnitedStatesCustomary.Yard
 import kotlin.math.pow
-import kotlin.math.roundToInt
+import kotlin.math.roundToLong
 import org.jetbrains.compose.resources.StringResource
 import org.jetbrains.compose.resources.stringResource
 
@@ -36,11 +32,12 @@ public interface ScaleBarMeasure {
   public data object Metric : ScaleBarMeasure {
 
     override val stops: List<Length> =
-      buildStops(mantissas = listOf(1, 2, 5).map { it.meters }, exponents = -1..7)
+      buildStops(mantissas = listOf(1, 2, 5).map { it.toLength(Meter) }, exponents = -1..7)
 
     @Composable
     override fun getText(stop: Length): String =
-      if (stop >= 1.kilometers) stop.toDisplayString(Kilometer, Res.string.kilometers_symbol)
+      if (stop >= 1.toLength(Kilometer))
+        stop.toDisplayString(Kilometer, Res.string.kilometers_symbol)
       else stop.toDisplayString(Meter, Res.string.meters_symbol)
   }
 
@@ -49,14 +46,15 @@ public interface ScaleBarMeasure {
 
     override val stops: List<Length> =
       listOf(
-          buildStops(mantissas = listOf(1, 2, 5).map { it.feet }, exponents = -1..3).dropLast(1),
-          buildStops(mantissas = listOf(1, 2, 5).map { it.miles }, exponents = 0..4),
+          buildStops(mantissas = listOf(1, 2, 5).map { it.toLength(Foot) }, exponents = -1..3)
+            .dropLast(1),
+          buildStops(mantissas = listOf(1, 2, 5).map { it.toLength(Mile) }, exponents = 0..4),
         )
         .flatten()
 
     @Composable
     override fun getText(stop: Length): String =
-      if (stop >= 1.miles) stop.toDisplayString(Mile, Res.string.miles_symbol)
+      if (stop >= 1.toLength(Mile)) stop.toDisplayString(Mile, Res.string.miles_symbol)
       else stop.toDisplayString(Foot, Res.string.feet_symbol)
   }
 
@@ -65,14 +63,15 @@ public interface ScaleBarMeasure {
 
     override val stops: List<Length> =
       listOf(
-          buildStops(mantissas = listOf(1, 2, 5).map { it.yards }, exponents = -1..3).dropLast(2),
-          buildStops(mantissas = listOf(1, 2, 5).map { it.miles }, exponents = 0..4),
+          buildStops(mantissas = listOf(1, 2, 5).map { it.toLength(Yard) }, exponents = -1..3)
+            .dropLast(2),
+          buildStops(mantissas = listOf(1, 2, 5).map { it.toLength(Mile) }, exponents = 0..4),
         )
         .flatten()
 
     @Composable
     override fun getText(stop: Length): String =
-      if (stop >= 1.miles) stop.toDisplayString(Mile, Res.string.miles_symbol)
+      if (stop >= 1.toLength(Mile)) stop.toDisplayString(Mile, Res.string.miles_symbol)
       else stop.toDisplayString(Yard, Res.string.yards_symbol)
   }
 }
@@ -92,5 +91,6 @@ private fun buildStops(mantissas: List<Length>, exponents: IntRange) = buildList
 }
 
 // https://github.com/kevincianfarini/alchemist/issues/53
+// https://github.com/kevincianfarini/alchemist/issues/54
 private operator fun Length.times(other: Double) =
-  (this.toDouble(LengthUnit.International.Nanometer) * other).roundToInt().nanometers
+  (this.toLong(Nanometer) * other).roundToLong().toLength(Nanometer)

lib/maplibre-compose/src/androidMain/kotlin/dev/sargunv/maplibrecompose/core/AndroidMap.kt

@@ -24,6 +24,9 @@ import dev.sargunv.maplibrecompose.expressions.value.BooleanValue
 import io.github.dellisd.spatialk.geojson.BoundingBox
 import io.github.dellisd.spatialk.geojson.Feature
 import io.github.dellisd.spatialk.geojson.Position
+import io.github.kevincianfarini.alchemist.scalar.toLength
+import io.github.kevincianfarini.alchemist.type.Length
+import io.github.kevincianfarini.alchemist.unit.LengthUnit.International.Meter
 import kotlin.coroutines.resume
 import kotlin.coroutines.suspendCoroutine
 import kotlin.time.Duration
@@ -335,8 +338,10 @@ internal class AndroidMap(
       .map { Feature.fromJson(it.toJson()) }
   }
 
-  override fun metersPerDpAtLatitude(latitude: Double) =
-    map.projection.getMetersPerPixelAtLatitude(latitude)
+  override fun lengthPerDpAtLatitude(latitude: Double): Length {
+    // https://github.com/kevincianfarini/alchemist/issues/54
+    return map.projection.getMetersPerPixelAtLatitude(latitude).toLength(Meter)
+  }
 }
 
 private fun MLNVisibleRegion.toVisibleRegion() =

lib/maplibre-compose/src/commonMain/kotlin/dev/sargunv/maplibrecompose/compose/CameraState.kt

@@ -17,6 +17,9 @@ import dev.sargunv.maplibrecompose.expressions.value.BooleanValue
 import io.github.dellisd.spatialk.geojson.BoundingBox
 import io.github.dellisd.spatialk.geojson.Feature
 import io.github.dellisd.spatialk.geojson.Position
+import io.github.kevincianfarini.alchemist.scalar.toLength
+import io.github.kevincianfarini.alchemist.type.Length
+import io.github.kevincianfarini.alchemist.unit.LengthUnit.International.Meter
 import kotlin.time.Duration
 import kotlin.time.Duration.Companion.milliseconds
 import kotlinx.coroutines.channels.Channel
@@ -42,7 +45,8 @@ public class CameraState internal constructor(firstPosition: CameraPosition) {
 
   internal val positionState = mutableStateOf(firstPosition)
   internal val moveReasonState = mutableStateOf(CameraMoveReason.NONE)
-  internal val metersPerDpAtTargetState = mutableStateOf(0.0)
+  // https://github.com/kevincianfarini/alchemist/issues/54
+  internal val lengthPerDpAtTargetState = mutableStateOf(0.toLength(Meter))
 
   /** how the camera is oriented towards the map */
   // if the map is not yet initialized, we store the value to apply it later
@@ -57,9 +61,9 @@ public class CameraState internal constructor(firstPosition: CameraPosition) {
   public val moveReason: CameraMoveReason
     get() = moveReasonState.value
 
-  /** meters per dp at the target position */
-  public val metersPerDpAtTarget: Double
-    get() = metersPerDpAtTargetState.value
+  /** real world distance per dp at the target position */
+  public val lengthPerDpAtTarget: Length
+    get() = lengthPerDpAtTargetState.value
 
   /** suspends until the map has been initialized */
   public suspend fun awaitInitialized() {

lib/maplibre-compose/src/commonMain/kotlin/dev/sargunv/maplibrecompose/compose/MaplibreMap.kt

@@ -115,8 +115,8 @@ public fun MaplibreMap(
           map as StandardMaplibreMap
           styleState.attach(style)
           rememberedStyle = style
-          cameraState.metersPerDpAtTargetState.value =
-            map.metersPerDpAtLatitude(map.getCameraPosition().target.latitude)
+          cameraState.lengthPerDpAtTargetState.value =
+            map.lengthPerDpAtLatitude(map.getCameraPosition().target.latitude)
         }
 
         override fun onCameraMoveStarted(map: MaplibreMap, reason: CameraMoveReason) {
@@ -126,8 +126,8 @@ public fun MaplibreMap(
         override fun onCameraMoved(map: MaplibreMap) {
           map as StandardMaplibreMap
           cameraState.positionState.value = map.getCameraPosition()
-          cameraState.metersPerDpAtTargetState.value =
-            map.metersPerDpAtLatitude(map.getCameraPosition().target.latitude)
+          cameraState.lengthPerDpAtTargetState.value =
+            map.lengthPerDpAtLatitude(map.getCameraPosition().target.latitude)
         }
 
         override fun onCameraMoveEnded(map: MaplibreMap) {}