Add blendMode property to ArcGIS API for JavaScript 4.x

[tianleili]

I draw polylines in ArcGIS API for JavaScript 4.x. When the polylines is very dense, there will be no bright effect of gathering. In other libraries, such as echarts, there is an attribute blendMode to handle this situation, which calls ctx.globalCompositeOperation = "lighter" to display the aggregation effect. Can ArcGIS API for JavaScript provide a similar approach?

[KristianEkenes]

The JS API does support various blend modes and effects on the layer level. 

https://developers.arcgis.com/javascript/latest/api-reference/esri-layers-FeatureLayer.html#blendMod...

https://developers.arcgis.com/javascript/latest/api-reference/esri-layers-FeatureLayer.html#effect 

We also have a guide to visualizing high density data where we talk about bloom as a way to accomplish this: https://developers.arcgis.com/javascript/latest/visualization/high-density-data/bloom/

There are other techniques as well, like using opacity. Hopefully this helps.