PathStyleExtension

lonboard.layer_extension.PathStyleExtension

Adds selected features to the PathLayer and composite layers that render the PathLayer, e.g. PolygonLayer.

Example

Deck.gl example deck.gl/docs/api-reference/extensions/path-style-extension

Layer Properties

This extension dynamically enables the following properties onto the layer(s) where it is included:

get_dash_array

Must be specified if the dash option is enabled. The dash array to draw each path with [dash_size, gap_size] relative to the width of the path.

• Type: DashArrayAccessor, optional
  • If a scalar value is provided, it is used as the value for all objects. Pass [0, 0] to draw the path in solid line.
  • If an array is provided, each value in the array will be used as the value for the object at the same row index.
• Default: [0, 0].

dash_justified

Only effective if get_dash_array is specified. If True, adjust gaps for the dashes to align at both ends. Overrides the effect of high_precision_dash.

• Type: boolean, optional
• Default False.

get_offset

Must be specified if the offset option is enabled.

The offset to draw each path with, relative to the width of the path. Negative offset is to the left hand side, and positive offset is to the right hand side. 0 extrudes the path so that it is centered at the specified coordinates.

• Type: FloatAccessor, optional
  • If a number is provided, it is used as the offset for all objects.
  • If an array is provided, each value in the array will be used as the offset for the object at the same row index.
• Default: None.

dash_gap_pickable

Only effective if get_dash_array is specified. If True, gaps between solid strokes are pickable. If False, only the solid strokes are pickable.

Remarks

Limitations

WebGL2 has guaranteed support for up to 16 attributes per shader. The current implementation of PathLayer uses 13 attributes. Each one of the options of this extension adds one more attribute. In other words, if all options are enabled, the layer will not be able to use other extensions.

Tips on Rendering Dash Lines

There are three modes to render dash lines with this extension:

1. Default: dash starts from the beginning of each line segment
2. Justified: dash is stretched to center on each line segment
3. High precision: dash is evaluated continuously from the beginning of a path

The above table illustrates the visual behavior of the three modes.

The default mode works best if the data consists of long, disjoint paths. It renders dashes at exactly the defined lengths.

The justified mode is guaranteed to render sharp, well-defined corners. This is great for rendering polyline shapes. However, the gap size may look inconsistent across line segments due to stretching.

The high precision mode pre-calculates path length on the CPU, so it may be slower and use more resources for large datasets. When a path contains a lot of short segments, this mode yields the best result.

dash class-attribute instance-attribute

dash = tag(sync=True)

Add capability to render dashed lines.

• Type: boolean, optional
• Default False.

high_precision_dash class-attribute instance-attribute

high_precision_dash = tag(sync=True)

Improve dash rendering quality in certain circumstances.

Note that this option introduces additional performance overhead. See "Remarks".

• Type: boolean, optional
• Default False.

offset class-attribute instance-attribute

offset = tag(sync=True)

Add capability to offset lines.

• Type: boolean, optional
• Default False.