Custom Drawing on Mapbox Map Canvas

Question

I would like to be able to manually draw complex shapes on a mapbox map using the android sdk. I have inherited the map view class and overridden the ondraw event but unfortunately whatever I draw gets over drawn by the map itself.

As an example I need to be able to draw polygons with diamond shaped borders among other complex shapes. This i can do no problem in GoogleMaps using a custom tile provider and overriding ondraw.

Here is the only code I have so far for mapbox:

    @Override
    public void onDraw(Canvas canvas) {        
        super.onDraw(canvas);

        Paint stroke = new Paint();
        stroke.setColor(Color.BLACK);
        stroke.setStyle(Paint.Style.STROKE);
        stroke.setStrokeWidth(5);
        stroke.setAntiAlias(true); 

        canvas.drawLine(0f,0f,1440f,2464f,stroke);
    }

Answer 1

You can do what You want by 2 ways:

1) as You propose: "inherit the MapView class and overridden the onDraw() event". But MapView extends FrameLayout which is ViewGroup, so You should override dispatchDraw() instead of onDraw().

This approach requires custom view, which extends MapViewand implements:

• drawing over the MapView;

• customizing line styles ("diamonds instead of a simple line");

• binding path to Lat/Lon coordinates of MapView.

For drawing over the MapView You should override dispatchDraw(), for example like this:

@Override
public void dispatchDraw(Canvas canvas) {
    super.dispatchDraw(canvas);
    canvas.save();
    drawDiamondsPath(canvas);
    canvas.restore();
}

For customizing line styles You can use setPathEffect() method of Paint class. For this You should create path for "diamond stamp" (in pixels), which will repeated every "advance" (in pixels too):

        mPathDiamondStamp = new Path();
        mPathDiamondStamp.moveTo(-DIAMOND_WIDTH / 2, 0);
        mPathDiamondStamp.lineTo(0, DIAMOND_HEIGHT / 2);
        mPathDiamondStamp.lineTo(DIAMOND_WIDTH / 2, 0);
        mPathDiamondStamp.lineTo(0, -DIAMOND_HEIGHT / 2);
        mPathDiamondStamp.close();

        mPathDiamondStamp.moveTo(-DIAMOND_WIDTH / 2 + DIAMOND_BORDER_WIDTH, 0);
        mPathDiamondStamp.lineTo(0, -DIAMOND_HEIGHT / 2 + DIAMOND_BORDER_WIDTH / 2);
        mPathDiamondStamp.lineTo(DIAMOND_WIDTH / 2 - DIAMOND_BORDER_WIDTH, 0);
        mPathDiamondStamp.lineTo(0, DIAMOND_HEIGHT / 2 - DIAMOND_BORDER_WIDTH / 2);
        mPathDiamondStamp.close();

        mPathDiamondStamp.setFillType(Path.FillType.EVEN_ODD);

        mDiamondPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
        mDiamondPaint.setColor(Color.BLUE);
        mDiamondPaint.setStrokeWidth(2);
        mDiamondPaint.setStyle(Paint.Style.FILL_AND_STROKE);
        mDiamondPaint.setStyle(Paint.Style.STROKE);
        mDiamondPaint.setPathEffect(new PathDashPathEffect(mPathDiamondStamp, DIAMOND_ADVANCE, DIAMOND_PHASE, PathDashPathEffect.Style.ROTATE));

(in this case there are 2 Path - first one (clockwise) for outer border and second (counter-clockwise) for inner border for "diamond" transparent "hole").

For binding path on screen to Lat/Lon coordinates of MapView You should have MapboxMap object of MapView - for that getMapAsync() and onMapReady() should be overridden:

@Override
public void getMapAsync(OnMapReadyCallback callback) {
    mMapReadyCallback = callback;
    super.getMapAsync(this);
}

@Override
public void onMapReady(MapboxMap mapboxMap) {
    mMapboxMap = mapboxMap;
    if (mMapReadyCallback != null) {
        mMapReadyCallback.onMapReady(mapboxMap);
    }
}

Than You can use it in "lat/lon-to-screen" convertating:

        mBorderPath = new Path();
        LatLng firstBorderPoint = mBorderPoints.get(0);
        PointF firstScreenPoint = mMapboxMap.getProjection().toScreenLocation(firstBorderPoint);
        mBorderPath.moveTo(firstScreenPoint.x, firstScreenPoint.y);

        for (int ixPoint = 1; ixPoint < mBorderPoints.size(); ixPoint++) {
            PointF currentScreenPoint = mMapboxMap.getProjection().toScreenLocation(mBorderPoints.get(ixPoint));
            mBorderPath.lineTo(currentScreenPoint.x, currentScreenPoint.y);
        }

Full source code:

Custom DrawMapView.java

public class DrawMapView extends MapView implements OnMapReadyCallback{

    private float DIAMOND_WIDTH = 42;
    private float DIAMOND_HEIGHT = 18;
    private float DIAMOND_ADVANCE = 1.5f * DIAMOND_WIDTH;       // spacing between each stamp of shape
    private float DIAMOND_PHASE = DIAMOND_WIDTH / 2;            // amount to offset before the first shape is stamped
    private float DIAMOND_BORDER_WIDTH = 6;                     // width of diamond border

    private Path mBorderPath;
    private Path mPathDiamondStamp;
    private Paint mDiamondPaint;
    private OnMapReadyCallback mMapReadyCallback;
    private MapboxMap mMapboxMap = null;
    private List<LatLng> mBorderPoints;

    public DrawMapView(@NonNull Context context) {
        super(context);
        init();
    }

    public DrawMapView(@NonNull Context context, @Nullable AttributeSet attrs) {
        super(context, attrs);
        init();
    }

    public DrawMapView(@NonNull Context context, @Nullable AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        init();
    }

    public DrawMapView(@NonNull Context context, @Nullable MapboxMapOptions options) {
        super(context, options);
        init();
    }

    public void setBorderPoints(List<LatLng> borderPoints) {
        mBorderPoints = borderPoints;
    }

    @Override
    public void getMapAsync(OnMapReadyCallback callback) {
        mMapReadyCallback = callback;
        super.getMapAsync(this);
    }

    @Override
    public void onMapReady(MapboxMap mapboxMap) {
        mMapboxMap = mapboxMap;
        if (mMapReadyCallback != null) {
            mMapReadyCallback.onMapReady(mapboxMap);
        }
    }

    @Override
    public void dispatchDraw(Canvas canvas) {
        super.dispatchDraw(canvas);
        canvas.save();
        drawDiamondsPath(canvas);
        canvas.restore();
    }

    private void drawDiamondsPath(Canvas canvas) {
        if (mBorderPoints == null || mBorderPoints.size() == 0) {
            return;
        }

        mBorderPath = new Path();

        LatLng firstBorderPoint = mBorderPoints.get(0);
        PointF firstScreenPoint = mMapboxMap.getProjection().toScreenLocation(firstBorderPoint);
        mBorderPath.moveTo(firstScreenPoint.x, firstScreenPoint.y);

        for (int ixPoint = 1; ixPoint < mBorderPoints.size(); ixPoint++) {
            PointF currentScreenPoint = mMapboxMap.getProjection().toScreenLocation(mBorderPoints.get(ixPoint));
            mBorderPath.lineTo(currentScreenPoint.x, currentScreenPoint.y);
        }

        mPathDiamondStamp = new Path();
        mPathDiamondStamp.moveTo(-DIAMOND_WIDTH / 2, 0);
        mPathDiamondStamp.lineTo(0, DIAMOND_HEIGHT / 2);
        mPathDiamondStamp.lineTo(DIAMOND_WIDTH / 2, 0);
        mPathDiamondStamp.lineTo(0, -DIAMOND_HEIGHT / 2);
        mPathDiamondStamp.close();

        mPathDiamondStamp.moveTo(-DIAMOND_WIDTH / 2 + DIAMOND_BORDER_WIDTH, 0);
        mPathDiamondStamp.lineTo(0, -DIAMOND_HEIGHT / 2 + DIAMOND_BORDER_WIDTH / 2);
        mPathDiamondStamp.lineTo(DIAMOND_WIDTH / 2 - DIAMOND_BORDER_WIDTH, 0);
        mPathDiamondStamp.lineTo(0, DIAMOND_HEIGHT / 2 - DIAMOND_BORDER_WIDTH / 2);
        mPathDiamondStamp.close();

        mPathDiamondStamp.setFillType(Path.FillType.EVEN_ODD);

        mDiamondPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
        mDiamondPaint.setColor(Color.BLUE);
        mDiamondPaint.setStrokeWidth(2);
        mDiamondPaint.setStyle(Paint.Style.FILL_AND_STROKE);
        mDiamondPaint.setStyle(Paint.Style.STROKE);
        mDiamondPaint.setPathEffect(new PathDashPathEffect(mPathDiamondStamp, DIAMOND_ADVANCE, DIAMOND_PHASE, PathDashPathEffect.Style.ROTATE));

        canvas.drawPath(mBorderPath, mDiamondPaint);
    }

    private void init() {
        mBorderPath = new Path();
        mPathDiamondStamp = new Path();
    }
}

ActivityMain.java

public class MainActivity extends AppCompatActivity {

    private DrawMapView mapView;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        MapboxAccountManager.start(this, getString(R.string.access_token));
        setContentView(R.layout.activity_main);

        mapView = (DrawMapView) findViewById(R.id.mapView);
        mapView.onCreate(savedInstanceState);
        mapView.getMapAsync(new OnMapReadyCallback() {
            @Override
            public void onMapReady(MapboxMap mapboxMap) {

                mapView.setBorderPoints(Arrays.asList(new LatLng(-36.930129, 174.958843),
                        new LatLng(-36.877860, 174.978108),
                        new LatLng(-36.846373, 174.901841),
                        new LatLng(-36.829215, 174.814659),
                        new LatLng(-36.791326, 174.779337),
                        new LatLng(-36.767680, 174.823242)));
            }
        });
    }

    @Override
    public void onResume() {
        super.onResume();
        mapView.onResume();
    }

    @Override
    public void onPause() {
        super.onPause();
        mapView.onPause();
    }

    @Override
    public void onSaveInstanceState(Bundle outState) {
        super.onSaveInstanceState(outState);
        mapView.onSaveInstanceState(outState);
    }

    @Override
    public void onLowMemory() {
        super.onLowMemory();
        mapView.onLowMemory();
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        mapView.onDestroy();
    }

}

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:mapbox="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="ua.com.omelchenko.mapboxlines.MainActivity">

    <ua.com.omelchenko.mapboxlines.DrawMapView
        android:id="@+id/mapView"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        mapbox:center_latitude="-36.841362"
        mapbox:center_longitude="174.851110"
        mapbox:style_url="@string/style_mapbox_streets"
        mapbox:zoom="10"/>
</RelativeLayout>

Finally, as a result, you should get something like this:

And You should take into account some "special cases", for example if all points of path is outside current view of map, there is no lines on it, even line should cross view of map and should be visible.

2) (better way) create and publish map with your additional lines and custom style for them (especially take a look at "Line patterns with Images" sections). You can use Mapbox Studio for this. And in this approach all "special cases" and performance issues is solved on Mabpox side.