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Subclassed Layers

deck.gl layers are designed to be easy to extend in order to add features. Subclassing allows redefining both layer life cycle methods as well as the vertex and/or fragment shaders.

If a small feature is missing from a layer, subclassing can often be a good technique to add it.

Overriding Attribute Calculation

// Example to add per-segment color to PathLayer
import {PathLayer} from '@deck.gl/layers';
import GL from '@luma.gl/constants';

// Allow accessor: `getColor` (Function, optional)
// Returns an color (array of numbers, RGBA) or array of colors (array of arrays).
export default class MultiColorPathLayer extends PathLayer {
  initializeState() {
    super.initializeState();
    this.getAttributeManager().addInstanced({
      instanceColors: {
        size: 4,
        type: GL.UNSIGNED_BYTE,
        normalized: true,
        update: this.calculateColors
      }
    })
  }

  calculateColors(attribute) {
    const {data, getPath, getColor} = this.props;
    const {value} = attribute;

    let i = 0;

    for (const object of data) {
      const path = getPath(object);
      const color = getColor(object);
      if (Array.isArray(color[0])) {
        if (color.length !== path.length) {
          throw new Error(`PathLayer getColor() returned a color array, but the number of
           colors returned doesn't match the number of segments in the path`);
        }
        color.forEach((segmentColor) => {
          value[i++] = segmentColor[0];
          value[i++] = segmentColor[1];
          value[i++] = segmentColor[2];
          value[i++] = isNaN(segmentColor[3]) ? 255 : segmentColor[3];
        });
      } else {
        for (let ptIndex = 1; ptIndex < path.length; ptIndex++) {
          value[i++] = color[0];
          value[i++] = color[1];
          value[i++] = color[2];
          value[i++] = isNaN(color[3]) ? 255 : color[3];
        }
      }
    }
  }
}

Courtesy of @dcposch.

Overriding Shaders

You can replace the shaders used in a layer by overriding the getShaders() method. Every core layer calls this method during initialization. It returns the shaders and modules used by the layer in an object:

  • vs: string, GLSL source of the vertex shader
  • fs: string, GLSL source of the fragment shader
  • modules: Array, list of shader modules to be used
  • inject: Object, map from injection points to custom GLSL code to be injected

Read about writing your own shaders.

When you are implementing your own custom layers, and want to change the shaders it is encouraged that you also define a getShaders() function and selectively overwrite required shader(s) with custom shaders. This makes it much easier for others to subclass your layer and make small changes to the shaders.

Note: When overwriting getShaders() you should pass down any unmodified shader(s) and modules as is. See code example below.

Defining Additional Uniforms

The best way to pass additional uniforms to your custom shader is to override the draw() method:

/// rounded-rectangle-layer.js
// Example to draw rounded rectangles instead of circles in ScatterplotLayer
import {ScatterplotLayer} from '@deck.gl/layers';
import customFragmentShader from './rounded-rectangle-layer-fragment';

export default RoundedRectangleLayer extends ScatterplotLayer {

  draw({uniforms}) {
    super.draw({
      uniforms:
        {
        ...uniforms,
        cornerRadius: this.props.cornerRadius
        }
    })
  }

  getShaders() {
    // use object.assign to make sure we don't overwrite existing fields like `vs`, `modules`...
    return Object.assign({}, super.getShaders(), {
      fs: customFragmentShader
    });
  }
}

RoundedRectangleLayer.defaultProps = {
  // cornerRadius: the amount of rounding at the rectangle corners
  // 0 - rectangle. 1 - circle.
  cornerRadius: 0.1
}

Modified fragment shader that uses this uniform (learn more in writing your own shaders):

/// rounded-rectangle-layer-fragment.js
// This is copied and adapted from scatterplot-layer-fragment.glsl.js
// Modifications are annotated
export default `\
#define SHADER_NAME rounded-rectangle-layer-fragment-shader

precision highp float;

uniform float cornerRadius;

varying vec4 vFillColor;
varying vec2 unitPosition;

void main(void) {

  float distToCenter = length(unitPosition);

  /* Calculate the cutoff radius for the rounded corners */
  float threshold = sqrt(2.0) * (1.0 - cornerRadius) + 1.0 * cornerRadius;
  if (distToCenter <= threshold) {
    gl_FragColor = vFillColor;
  } else {
    discard;
  }

  gl_FragColor = picking_filterHighlightColor(gl_FragColor);

  gl_FragColor = picking_filterPickingColor(gl_FragColor);
}
`;

Defining Additional Attributes

During initialization, you may define additional attributes by accessing the layer's attribute manager:

// my-point-cloud-layer.js
// Example to add per-point size to point cloud layer
import {PointCloudLayer} from 'deck.gl';
import vertexShader from 'my-point-cloud-layer-vertex';

export default MyPointCloudLayer extends PointCloudLayer {

  initializeState() {
    super.initializeState();

    this.state.attributeManager.addInstanced({
      instanceRadiusPixels: {size: 1, accessor: 'getRadius'}
    });
  }

  getShaders() {
    return Object.assign({}, super.getShaders(), {
      vs: vertexShader,
    });
  }
}

MyPointCloudLayer.defaultProps = {
  // returns point radius in pixels
  getRadius: {type: 'accessor', value: 1}
};

Modified vertex shader that uses this attribute (learn more in writing your own shaders):

// my-point-cloud-layer-vertex.js
// This is copied and adapted from point-cloud-layer-vertext.glsl.js
// Modifications are annotated
export default `\
#define SHADER_NAME point-cloud-layer-vertex-shader

attribute vec3 positions;
attribute vec3 instanceNormals;
attribute vec4 instanceColors;
attribute vec3 instancePositions;
attribute vec3 instancePositions64Low;
attribute vec3 instancePickingColors;

/* New attribute */
attribute flat instanceRadiusPixels;

uniform float opacity;

varying vec4 vColor;
varying vec2 unitPosition;

void main(void) {
  unitPosition = positions.xy;

  vec4 position_commonspace;
  gl_Position = project_position_to_clipspace(instancePositions, instancePositions64Low, vec3(0.), position_commonspace);
  /* replaced uniform 'radiusPixels' with 'instanceRadiusPixels' */
  gl_Position.xy += project_pixel_size_to_clipspace(positions.xy * instanceRadiusPixels);

  vec3 lightColor = lighting_getLightColor(instanceColors.rgb, project_uCameraPosition, position_commonspace.xyz, project_normal(instanceNormals));

  vColor = vec4(lightColor, instanceColors.a * opacity) / 255.0;

  picking_setPickingColor(instancePickingColors);
}
`;

Layer Extensions

Sometimes we need to subclass multiple layers to add similar functionalities. Layer extension is a way to generalize, reuse, and share subclassed layer code. Read on about how to package up a subclassed layer code into a layer extension.