DrawPolyline.md

title	Draw Polyline
tags	LineLayer ShapeSource onCameraChanged getCoordinateFromView Overlay
custom_props	example_rel_path LineLayer/DrawPolyline.tsx
custom_edit_url	https://github.com/rnmapbox/maps/tree/master/example/src/examples/LineLayer/DrawPolyline.tsx

This example shows a simple polyline editor. It uses onCameraChanged to get the center of the map and getCoordinateFromView to get the coordinates of the crosshair.

The crosshair is an overlay that is positioned using onLayout and getCoordinateFromView.

The ShapeSource is updated with the new coordinates and the LineLayer is updated with the new coordinates.

import { Camera, LineLayer, MapView, ShapeSource } from '@rnmapbox/maps';
import { Button, View } from 'react-native';
import React, {
  useState,
  useRef,
  ComponentProps,
  useMemo,
  forwardRef,
} from 'react';

type Position = [number, number];

type CrosshairProps = {
  size: number;
  w: number;
  onLayout: ComponentProps<typeof View>['onLayout'];
};
const Crosshair = forwardRef<View, CrosshairProps>(
  ({ size, w, onLayout }: CrosshairProps, ref) => (
    <View
      onLayout={onLayout}
      ref={ref}
      style={{
        width: 2 * size + 1,
        height: 2 * size + 1,
      }}
    >
      <View
        style={{
          position: 'absolute',
          left: size,
          top: 0,
          bottom: 0,
          borderColor: 'red',
          borderWidth: w / 2.0,
        }}
      />
      <View
        style={{
          position: 'absolute',
          top: size,
          left: 0,
          right: 0,
          borderColor: 'red',
          borderWidth: w / 2.0,
        }}
      />
    </View>
  ),
);

const CrosshairOverlay = ({
  onCenter,
}: {
  onCenter: (x: [number, number]) => void;
}) => {
  const ref = useRef<View>(null);

  return (
    <View
      style={{
        position: 'absolute',
        top: 0,
        left: 0,
        right: 0,
        bottom: 0,
        alignContent: 'center',
        alignItems: 'center',
        justifyContent: 'center',
      }}
      pointerEvents="none"
    >
      <Crosshair
        size={20}
        w={1.0}
        ref={ref}
        onLayout={(e) => {
          const { x, y, width, height } = e.nativeEvent.layout;
          onCenter([x + width / 2.0, y + height / 2.0]);
        }}
      />
    </View>
  );
};

const lineLayerStyle = {
  lineColor: '#ff0000',
};

const Polygon = ({ coordinates }: { coordinates: Position[] }) => {
  const features: GeoJSON.FeatureCollection = useMemo(() => {
    return {
      type: 'FeatureCollection',
      features: [
        {
          type: 'Feature',
          id: 'a-feature',
          geometry: {
            type: 'LineString',
            coordinates,
          },
          properties: {},
        } as const,
      ],
    };
  }, [coordinates]);
  console.log('=> features', JSON.stringify(features));
  return (
    <ShapeSource id={'shape-source-id-0'} shape={features}>
      <LineLayer id={'line-layer'} style={lineLayerStyle} />
    </ShapeSource>
  );
};

const DrawPolyline = () => {
  const [coordinates, setCoordinates] = useState<Position[]>([]);
  const [lastCoordinate, setLastCoordinate] = useState<Position>([0, 0]);
  const [started, setStarted] = useState(false);
  const [crosshairPos, setCrosshairPos] = useState([0, 0]);

  const coordinatesWithLast = useMemo(() => {
    return [...coordinates, lastCoordinate];
  }, [coordinates, lastCoordinate]);

  const map = useRef<MapView>(null);

  const newLocal = 'row';
  return (
    <View style={{ flex: 1 }}>
      <View>
        {!started ? (
          <Button
            title="start"
            onPress={() => {
              setStarted(true);
              setCoordinates([lastCoordinate]);
            }}
          />
        ) : (
          <View
            style={{
              flexDirection: newLocal,
              justifyContent: 'center',
              gap: 10,
            }}
          >
            <Button
              title="add"
              onPress={() => setCoordinates([...coordinates, lastCoordinate])}
            />
            <Button title="stop" onPress={() => setStarted(false)} />
          </View>
        )}
      </View>
      <View style={{ flex: 1 }}>
        <MapView
          ref={map}
          style={{ flex: 1 }}
          onCameraChanged={async (e) => {
            const crosshairCoords = await map.current?.getCoordinateFromView(
              crosshairPos,
            );
            console.log(
              'Crosshair coords: ',
              crosshairCoords,
              'camera center:',
              e.properties.center,
            );
            setLastCoordinate(crosshairCoords as Position);
            if (crosshairCoords && started) {
              setLastCoordinate(crosshairCoords as Position);
            }
          }}
        >
          {started && <Polygon coordinates={coordinatesWithLast} />}
          <Camera
            defaultSettings={{
              centerCoordinate: [-73.970895, 40.723279],
              zoomLevel: 12,
            }}
          />
        </MapView>
        <CrosshairOverlay onCenter={(c) => setCrosshairPos(c)} />
      </View>
    </View>
  );
};

export default DrawPolyline;

}