AggregationLayer

All of the layers in @deck.gl/aggregation-layers module perform some sort of data aggregation. All these layers perform aggregation with different parameters (CPU vs GPU, aggregation to rectangular bins vs hexagon bins, world space vs screen space, aggregation of single weight vs multiple weights etc).

AggregationLayer and GridAggregationLayer perform most of the common tasks for aggregation with flexibility of customizations. This document describes what AggregationLayer does and how to use it in other aggregation layers.

AggregationLayer is subclassed form CompositeLayer and all layers in @deck.gl/aggregation-layers are subclassed from this Layer.

Integration with AttributeManager

This layer creates AttributeManager and makes it available for its subclasses. Any aggregation layer can add attributes to the AttributeManager and retrieve them using getAttributes method. This enables using AttributeManager's features and optimization for using attributes. Also manual iteration of data prop can be removed and attributes can be directly set on GPU aggregation models or accessed directly for CPU aggregation.

Example: Adding attributes to an aggregation layer

const attributeManager = this.getAttributeManager();
attributeManager.add({
  positions: {size: 3, accessor: 'getPosition'},
  color: {size: 3, accessor: 'getColorWeight'},
  elevation: {size: 3, accessor: 'getElevationWeight'}
});

updateState()

During update state, Subclasses of AggregationLayer must first call 'super.updateState()', which calls

• updateShaders(shaders) : Subclasses can override this if they need to update shaders, for example, when performing GPU aggregation, aggregation shaders must be merged with argument of this function to correctly apply extensions.

• _updateAttributes: This checks and updates attributes based on updated props.

Checking if aggregation is dirty

Dimensions

Typical aggregation, involves :

1. Group the input data points into bins
2. Compute the aggregated value for each bin

For example, when cellSize or data is changed, layer needs to perform both 1 and 2 steps, when a parameter affecting a bin's value is changed (like getWeight accessor), layer only need to perform step 2.

When doing CPU Aggregation, both above steps are performed individually. But for GPU aggregation, both are merged into single render call.

To support what state is dirty, constructor takes dimensions object, which contains, several keyed dimensions. It must contain data dimension that defines, when re-aggregation needs to be performed.

isAggregationDirty()

This helper can be used if a dimension is changed. Sublayers can defined custom dimensions and call this method to check if a dimension is changed.

isAttributeChanged()

AggregationLayer tracks what attributes are changed in each update cycle. Super classes can use isAttributeChanged() method to check if a specific attribute is changed or any attribute is changed.