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feat(library): Add polyline progress utilities to SphericalUtil
This commit introduces two new utility functions to `SphericalUtil` for calculating points and prefixes on a polyline based on a percentage of its total length. A new demo has also been added to showcase this functionality. The key changes are: - **`SphericalUtil.getPointOnPolyline()`**: A new function that returns a `LatLng` at a specified percentage along a given polyline. - **`SphericalUtil.getPolylinePrefix()`**: A new function that returns a new list of `LatLng`s representing a prefix of the original polyline up to a specified percentage. - **New Demo**: A `PolylineProgressDemoActivity` has been added to the demo application. It demonstrates how to animate progress along a polyline using the new utility functions, complete with a `SeekBar` for user control. - **Tests**: Added comprehensive unit tests for `getPointOnPolyline` and `getPolylinePrefix` to ensure correctness and handle edge cases.
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‎demo/src/main/AndroidManifest.xml‎

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<activity
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android:name=".PolySimplifyDemoActivity"
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android:exported="true" />
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<activity
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android:name=".PolylineProgressDemoActivity"
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android:exported="true" />
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<activity
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android:name=".IconGeneratorDemoActivity"
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android:exported="true" />

‎demo/src/main/java/com/google/maps/android/utils/demo/MainActivity.java‎

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addDemo("Clustering: Force on Zoom", ZoomClusteringDemoActivity.class);
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addDemo("PolyUtil.decode", PolyDecodeDemoActivity.class);
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addDemo("PolyUtil.simplify", PolySimplifyDemoActivity.class);
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addDemo("Polyline Progress", PolylineProgressDemoActivity.class);
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addDemo("IconGenerator", IconGeneratorDemoActivity.class);
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addDemo("SphericalUtil.computeDistanceBetween", DistanceDemoActivity.class);
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addDemo("Generating tiles", TileProviderAndProjectionDemo.class);

‎demo/src/main/java/com/google/maps/android/utils/demo/PolylineProgressDemoActivity.kt‎

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package com.google.maps.android.utils.demo
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import android.graphics.Canvas
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import android.graphics.Color
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import android.os.Bundle
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import android.widget.Button
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import android.widget.SeekBar
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import android.widget.TextView
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import androidx.appcompat.app.AppCompatActivity
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import androidx.core.content.ContextCompat
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import androidx.lifecycle.MutableLiveData
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import com.google.android.gms.maps.CameraUpdateFactory
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import com.google.android.gms.maps.GoogleMap
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import com.google.android.gms.maps.OnMapReadyCallback
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import com.google.android.gms.maps.SupportMapFragment
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import com.google.android.gms.maps.model.BitmapDescriptor
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import com.google.android.gms.maps.model.BitmapDescriptorFactory
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import com.google.android.gms.maps.model.LatLng
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import com.google.android.gms.maps.model.Marker
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import com.google.android.gms.maps.model.MarkerOptions
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import com.google.android.gms.maps.model.Polyline
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import com.google.android.gms.maps.model.PolylineOptions
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import com.google.maps.android.SphericalUtil
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import kotlinx.coroutines.CoroutineScope
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import kotlinx.coroutines.Dispatchers
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import kotlinx.coroutines.Job
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import kotlinx.coroutines.delay
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import kotlinx.coroutines.launch
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import androidx.core.graphics.createBitmap
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import androidx.core.graphics.toColorInt
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class PolylineProgressDemoActivity : AppCompatActivity(), OnMapReadyCallback, SeekBar.OnSeekBarChangeListener {
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private var planeIcon: BitmapDescriptor? = null
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private lateinit var map: GoogleMap
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private lateinit var originalPolyline: Polyline
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private var progressPolyline: Polyline? = null
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private var progressMarker: Marker? = null
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private lateinit var seekBar: SeekBar
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private lateinit var percentageTextView: TextView
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private var isReady = false
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private var animationJob: Job? = null
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private val progress = MutableLiveData<Int>()
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private val direction = MutableLiveData<Int>()
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private val stepSize = 1
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private val polylinePoints = listOf(
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LatLng(40.7128, -74.0060), // New York
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LatLng(34.0522, -118.2437), // Los Angeles
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LatLng(41.8781, -87.6298), // Chicago
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LatLng(29.7604, -95.3698), // Houston
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LatLng(39.9526, -75.1652) // Philadelphia
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)
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override fun onCreate(savedInstanceState: Bundle?) {
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super.onCreate(savedInstanceState)
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isReady = false
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setContentView(R.layout.activity_polyline_progress_demo)
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val mapFragment = supportFragmentManager.findFragmentById(R.id.map) as SupportMapFragment
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mapFragment.getMapAsync(this)
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progress.value = 0
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direction.value = 1
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}
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override fun onMapReady(googleMap: GoogleMap) {
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map = googleMap
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isReady = true
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planeIcon = bitmapDescriptorFromVector(R.drawable.baseline_airplanemode_active_24, "#FFD700".toColorInt())
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originalPolyline = map.addPolyline(
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PolylineOptions()
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.addAll(polylinePoints)
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.color(Color.GRAY)
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.width(15f) // Set the width of the base polyline
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.geodesic(true) // Be sure to set the geodesic flag!
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)
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val bounds = with(com.google.android.gms.maps.model.LatLngBounds.Builder()) {
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for (point in polylinePoints) {
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include(point)
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}
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build()
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}
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map.moveCamera(CameraUpdateFactory.newLatLngBounds(bounds, 100))
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percentageTextView = findViewById(R.id.percentageTextView)
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seekBar = findViewById<SeekBar>(R.id.seekBar).also {
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it.setOnSeekBarChangeListener(this)
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it.progress = 0
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}
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findViewById<Button>(R.id.resetButton).setOnClickListener {
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if (animationJob != null) {
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animationJob?.cancel()
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animationJob = null
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}
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direction.value = 1
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progress.value = 0
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startAnimation()
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}
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findViewById<Button>(R.id.pauseButton).setOnClickListener {
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if (animationJob != null) {
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animationJob?.cancel()
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animationJob = null
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} else {
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startAnimation()
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}
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}
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progress.observe(this) {
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seekBar.progress = it
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percentageTextView.text = "$it%"
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updateProgress(it / 100.0)
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}
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startAnimation()
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}
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private fun startAnimation() {
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stopAnimation() // Stop any existing animation first
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// Start a coroutine to animate the polyline progress
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animationJob = CoroutineScope(Dispatchers.Main).launch {
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while (true) {
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val currentProgress = progress.value ?: 0
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val currentDirection = direction.value ?: 1
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var nextProgress = currentProgress + currentDirection * stepSize
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if (nextProgress >= 100) {
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nextProgress = 100
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direction.value = -1
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} else if (nextProgress <= 0) {
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nextProgress = 0
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direction.value = 1
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}
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progress.value = nextProgress
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delay(50)
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}
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}
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}
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private fun stopAnimation() {
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animationJob?.cancel()
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animationJob = null
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}
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override fun onPause() {
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super.onPause()
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animationJob?.cancel()
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}
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override fun onResume() {
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super.onResume()
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startAnimation()
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}
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override fun onProgressChanged(seekBar: SeekBar?, progress: Int, fromUser: Boolean) {
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if (fromUser) {
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stopAnimation()
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this.progress.value = progress
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}
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}
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override fun onStartTrackingTouch(seekBar: SeekBar?) {}
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override fun onStopTrackingTouch(seekBar: SeekBar?) {}
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private fun updateProgress(percentage: Double) {
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if (!isReady) return
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progressPolyline?.remove()
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val prefix = SphericalUtil.getPolylinePrefix(polylinePoints, percentage)
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if (prefix.isNotEmpty()) {
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progressPolyline = map.addPolyline(
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PolylineOptions()
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.addAll(prefix)
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.color(Color.BLUE)
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.width(7f) // Set the width of the progress polyline
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.zIndex(1f) // Set the z-index to draw it on top
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.geodesic(true) // Be sure to set the geodesic flag!
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)
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}
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val point = SphericalUtil.getPointOnPolyline(polylinePoints, percentage)
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if (point != null) {
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// Get the next point to calculate the heading
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val nextPoint = SphericalUtil.getPointOnPolyline(polylinePoints, percentage + 0.0001)
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var heading = nextPoint?.let { SphericalUtil.computeHeading(point, it) }
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if (direction.value == -1) {
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heading = heading?.plus(180)
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}
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if (progressMarker == null) {
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progressMarker = map.addMarker(
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MarkerOptions()
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.position(point)
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.flat(true)
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.draggable(false)
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.also {
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if (heading != null) {
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it.rotation(heading.toFloat())
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}
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if (planeIcon != null) {
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it.icon(planeIcon)
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}
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}
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)
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} else {
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progressMarker?.position = point
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if (heading != null) {
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progressMarker?.rotation = heading.toFloat()
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}
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}
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}
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}
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private fun bitmapDescriptorFromVector(vectorResId: Int, color: Int): BitmapDescriptor? {
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return ContextCompat.getDrawable(this, vectorResId)?.run {
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setTint(color)
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setBounds(0, 0, intrinsicWidth, intrinsicHeight)
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val bitmap = createBitmap(intrinsicWidth, intrinsicHeight)
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val canvas = Canvas(bitmap)
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draw(canvas)
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BitmapDescriptorFactory.fromBitmap(bitmap)
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}
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}
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}

‎demo/src/main/res/drawable/baseline_airplanemode_active_24.xml‎

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<vector xmlns:android="http://schemas.android.com/apk/res/android" android:height="24dp" android:tint="#000000" android:viewportHeight="24" android:viewportWidth="24" android:width="24dp">
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<path android:fillColor="@android:color/white" android:pathData="M22,16v-2l-8.5,-5V3.5C13.5,2.67 12.83,2 12,2s-1.5,0.67 -1.5,1.5V9L2,14v2l8.5,-2.5V19L8,20.5L8,22l4,-1l4,1l0,-1.5L13.5,19v-5.5L22,16z"/>
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</vector>

‎demo/src/main/res/layout/activity_polyline_progress_demo.xml‎

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<?xml version="1.0" encoding="utf-8"?>
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<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
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android:layout_width="match_parent"
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android:layout_height="match_parent"
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android:orientation="vertical">
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<RelativeLayout
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android:layout_width="match_parent"
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android:layout_height="wrap_content"
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android:layout_marginVertical="24dp"
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android:layout_marginHorizontal="16dp">
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<SeekBar
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android:id="@+id/seekBar"
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android:layout_width="match_parent"
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android:layout_height="wrap_content"
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android:layout_toStartOf="@+id/percentageTextView"
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android:layout_centerVertical="true"
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android:max="100" />
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<TextView
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android:id="@+id/percentageTextView"
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android:layout_width="wrap_content"
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android:layout_height="wrap_content"
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android:layout_alignParentEnd="true"
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android:layout_centerVertical="true"
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android:text="0%%"
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android:minWidth="40dp"
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android:gravity="center"
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/>
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</RelativeLayout>
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<LinearLayout
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android:layout_width="match_parent"
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android:layout_height="wrap_content"
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android:orientation="horizontal">
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<Button
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android:id="@+id/resetButton"
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android:layout_width="0dp"
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android:layout_height="wrap_content"
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android:layout_marginHorizontal="16dp"
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android:layout_weight="1"
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android:text="Restart" />
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<Button
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android:id="@+id/pauseButton"
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android:layout_width="0dp"
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android:layout_marginHorizontal="16dp"
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android:layout_height="wrap_content"
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android:layout_weight="1"
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android:text="Pause" />
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</LinearLayout>
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<fragment
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android:id="@+id/map"
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class="com.google.android.gms.maps.SupportMapFragment"
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android:layout_width="match_parent"
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android:layout_height="0dp"
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android:layout_weight="1" />
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</LinearLayout>

‎library/src/main/java/com/google/maps/android/SphericalUtil.kt‎

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val t = tan1 * tan2
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return 2 * atan2(t * sin(deltaLng), 1 + t * cos(deltaLng))
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}
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/**
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* Returns the point on a polyline that is a given percentage of the total length of the
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* polyline.
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*
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* @param polyline the polyline
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* @param percentage the percentage of the total length of the polyline to find the point for
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* @return the `LatLng` of the point on the polyline, or `null` if the polyline is empty or
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* the percentage is outside the range [0, 1]
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*/
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@JvmStatic
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fun getPointOnPolyline(polyline: List<LatLng>, percentage: Double): LatLng? {
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return getPolylinePrefix(polyline, percentage).lastOrNull()
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}
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/**
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* Returns a new polyline that is a prefix of the original polyline, representing a given
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* percentage of the original polyline's length.
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*
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* Note: The returned polyline should be displayed on the map with `geodesic` set to `true`
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* to ensure it follows the same spherical path as the calculation.
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*
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* @param polyline the original polyline
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* @param percentage the percentage of the original polyline's length to include in the prefix
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* @return a new polyline representing the prefix, or an empty list if the original polyline
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* is empty or the percentage is outside the range [0, 1]
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*/
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@JvmStatic
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fun getPolylinePrefix(polyline: List<LatLng>, percentage: Double): List<LatLng> {
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if (polyline.isEmpty() || percentage !in 0.0..1.0) {
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return emptyList()
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}
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when (percentage) {
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0.0 -> return listOf(polyline.first())
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1.0 -> return polyline.toList() // Return a defensive copy
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}
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val targetDistance = computeLength(polyline) * percentage
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return buildList {
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add(polyline.first())
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var accumulatedDistance = 0.0
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for ((p1, p2) in polyline.zipWithNext()) {
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val segmentLength = computeDistanceBetween(p1, p2)
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if (accumulatedDistance + segmentLength >= targetDistance) {
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val fraction = (targetDistance - accumulatedDistance) / segmentLength
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add(interpolate(p1, p2, fraction))
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return@buildList // We're done, so exit the builder
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}
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add(p2)
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accumulatedDistance += segmentLength
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}
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}
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}
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}

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