RFC for implementing triangulation of polygons in loader web worker for MVTLayers

[felixpalmer]

RFC for implementing triangulation of polygons in loader web worker for MVTLayers

[coveralls]

Coverage remained the same at 82.154% when pulling 5829c19 on felix/rfc-loader-worker-triangulation into d5bb542 on master.

[Pessimistress]

The PolygonTesselator already supports externally supplied indices: https://github.com/visgl/deck.gl/blob/master/modules/layers/src/solid-polygon-layer/polygon-tesselator.js#L125

[felixpalmer]

@Pessimistress could you point me in the right direction on how to actually pass these indices to the PolygonTesselator? I'm struggling to see where I can set a prop or something to pass them in.

[felixpalmer]

I can pass the index data down to the SolidPolygonLayer OK and then in the constructor for the PolygonTesselator

deck.gl/modules/layers/src/solid-polygon-layer/solid-polygon-layer.js

Line 89 in 7decad2

polygonTesselator: new PolygonTesselator({

I set the buffers prop to include the indices:

polygonTesselator: new PolygonTesselator({
  ...
  buffers: this.props.data.triangles ? {
    indices: this.props.data.triangles
  } : {}
})

This then means that externalIndices is correctly set in PolygonTesselator.updateGeometry(), but then this doesn't prevent the _updateIndices being invoked and thus earcut recomputing the triangulation.

[Pessimistress]

indices is passed as part of data.attributes, the same way you supply externally packed positions. See https://deck.gl/docs/developer-guide/performance#supply-attributes-directly

[felixpalmer]

@Pessimistress thanks for the input, I've updated the RFC based on your comments

[ibgreen]

Finally had some time to comment. This looks good and no flags.

For the record, my approach would have been:

• Add a fork of earcut into math.gl. Could go into the existing polygons sub module or a new sub module.
• The fork would be optimized for binary arrays, we'd add benchmarks and "optimize it to the bone".
• The fork could including any additional general processing done by deck.gl (indices etc).

If we want to "move" earcut directly to loaders.gl (perhaps as a first step) we can do it in the @loaders.gl/math module which is a staging area for things we want to move to math.gl eventually.

We definitely want to offer this option for all geometry loaders in loaders.gl (Geojson, Shapefile, CSV with embedded WKT etc but for now I think it fine to focus on MVT).

[alasarr]

I'd set as default during a short period of time, after that, I'd make it true

[alasarr]

@felixpalmer I think we can consider @ibgreen's approach and move it to @loaders.gl/math