PathLayer

The Path Layer takes in lists of coordinate points and renders them as extruded lines with mitering.

import DeckGL from '@deck.gl/react';
import {PathLayer} from '@deck.gl/layers';

function App({data, viewState}) {
  /**
   * Data format:
   * [
   *   {
   *     path: [[-122.4, 37.7], [-122.5, 37.8], [-122.6, 37.85]],
   *     name: 'Richmond - Millbrae',
   *     color: [255, 0, 0]
   *   },
   *   ...
   * ]
   */
  const layer = new PathLayer({
    id: 'path-layer',
    data,
    pickable: true,
    widthScale: 20,
    widthMinPixels: 2,
    getPath: d => d.path,
    getColor: d => colorToRGBArray(d.color),
    getWidth: d => 5
  });

  return <DeckGL viewState={viewState}
    layers={[layer]}
    getTooltip={({object}) => object && object.name} />;
}

Installation

To install the dependencies from NPM:

npm install deck.gl
# or
npm install @deck.gl/core @deck.gl/layers

import {PathLayer} from '@deck.gl/layers';
new PathLayer({});

To use pre-bundled scripts:

<script src="https://unpkg.com/deck.gl@^8.0.0/dist.min.js"></script>
<!-- or -->
<script src="https://unpkg.com/@deck.gl/core@^8.0.0/dist.min.js"></script>
<script src="https://unpkg.com/@deck.gl/layers@^8.0.0/dist.min.js"></script>

new deck.PathLayer({});

Properties

Inherits from all Base Layer properties.

Render Options

widthUnits (String, optional)

• Default: 'meters'

The units of the line width, one of 'meters', 'common', and 'pixels'. See unit system.

widthScale (Number, optional)

• Default: 1

The path width multiplier that multiplied to all paths.

widthMinPixels (Number, optional)

• Default: 0

The minimum path width in pixels. This prop can be used to prevent the path from getting too thin when zoomed out.

widthMaxPixels (Number, optional)

• Default: Number.MAX_SAFE_INTEGER

The maximum path width in pixels. This prop can be used to prevent the path from getting too thick when zoomed in.

capRounded (Boolean, optional)

• Default: false

Type of caps. If true, draw round caps. Otherwise draw square caps.

jointRounded (Boolean, optional)

• Default: false

Type of joint. If true, draw round joints. Otherwise draw miter joints.

billboard (Boolean, optional)

• Default: false

If true, extrude the path in screen space (width always faces the camera). If false, the width always faces up.

miterLimit (Number, optional)

• Default: 4

The maximum extent of a joint in ratio to the stroke width. Only works if jointRounded is false.

_pathType (Object, optional)

• Default: null

Note: This prop is experimental

One of null, 'loop' or 'open'.

If 'loop' or 'open', will skip normalizing the coordinates returned by getPath and instead assume all paths are to be loops or open paths. Disabling normalization improves performance during data update, but makes the layer prone to error in case the data is malformed. It is only recommended when you use this layer with preprocessed static data or validation on the backend.

When normalization is disabled, paths must be specified in the format of flat array. Open paths must contain at least 2 vertices and closed paths must contain at least 3 vertices. See getPath below for details.

Data Accessors

getPath (Function, optional)

• Default: object => object.path

Called on each object in the data stream to retrieve its corresponding path.

A path can be one of the following formats:

• An array of points ([x, y, z]). Compatible with the GeoJSON LineString specification.
• A flat array or TypedArray of numbers, in the shape of [x0, y0, z0, x1, y1, z1, ...]. By default, each coordinate is assumed to contain 3 consecutive numbers. If each coordinate contains only two numbers (x, y), set the positionFormat prop of the layer to XY:

new PathLayer({
  ...
  getPath: object => object.vertices, // [x0, y0, x1, y1, x2, y2, ...]
  positionFormat: `XY`
})

getColor (Function|Array, optional)

• Default [0, 0, 0, 255]

The rgba color of each object, in r, g, b, [a]. Each component is in the 0-255 range.

• If an array is provided, it is used as the color for all objects.
• If a function is provided, it is called on each object to retrieve its color.

getWidth (Function|Number, optional)

• Default: 1

The width of each path, in units specified by widthUnits (default meters).

• If a number is provided, it is used as the width for all paths.
• If a function is provided, it is called on each path to retrieve its width.

Use binary attributes

This section is about the special requirements when supplying attributes directly to a PathLayer.

Because each path has a different number of vertices, when data.attributes.getPath is supplied, the layer also requires an array data.startIndices that describes the vertex index at the start of each path. For example, if there are 3 paths of 2, 3, and 4 vertices each, startIndices should be [0, 2, 5, 9].

Additionally, all other attributes (getColor, getWidth, etc.), if supplied, must contain the same layout (number of vertices) as the getPath buffer.

To truly realize the performance gain from using binary data, the app likely wants to skip all data processing in this layer. Specify the _pathType prop to skip normalization.

Example use case:

// USE PLAIN JSON OBJECTS
const PATH_DATA = [
  {
    path: [[-122.4, 37.7], [-122.5, 37.8], [-122.6, 37.85]],
    name: 'Richmond - Millbrae',
    color: [255, 0, 0]
  },
  ...
];

new PathLayer({
  data: PATH_DATA,
  getPath: d => d.path,
  getColor: d => d.color
})

Convert to using binary attributes:

// USE BINARY
// Flatten the path vertices
// [-122.4, 37.7, -122.5, 37.8, -122.6, 37.85, ...]
const positions = new Float64Array(PATH_DATA.map(d => d.path).flat(2));
// The color attribute must supply one color for each vertex
// [255, 0, 0, 255, 0, 0, 255, 0, 0, ...]
const colors = new Uint8Array(PATH_DATA.map(d => d.path.map(_ => d.color)).flat(2));
// The "layout" that tells PathLayer where each path starts
const startIndices = new Uint16Array(PATH_DATA.reduce((acc, d) => {
  const lastIndex = acc[acc.length - 1];
  acc.push(lastIndex + d.path.length);
  return acc;
}, [0]));

new PathLayer({
  data: {
    length: PATH_DATA.length,
    startIndices: startIndices, // this is required to render the paths correctly!
    attributes: {
      getPath: {value: positions, size: 2},
      getColor: {value: colors, size: 3}
    }
  },
  _pathType: 'open' // this instructs the layer to skip normalization and use the binary as-is
})

Source

modules/layers/src/path-layer