Conditional port coloring

In this example, we will fill the port shape with a color that is determined by the number of connected edges. Ports with no connections will be filled green, ports with 10 or more connections will be filled red. Values between 0 and 10 will result in the hue blended between green and red. Alternatively, the color from the port’s tag is used, if defined.

We introduce two methods that get the port color from the tag, or calculate the hue based on the port’s degree. For this purpose, we get the IGraph from the IRenderContext.

private getColor(graph: IGraph, port: IPort): string {
  return port.tag?.color ?? this.calculateColorByDegree(graph, port)
}

private calculateColorByDegree(graph: IGraph, port: IPort): string {
  // get the number of edges connected to the port
  const portDegree = graph.degree(port)
  const ratio = Math.min(portDegree / 10, 1)
  const hue = (1 - ratio) * 100
  return `hsl(${hue}deg 100% 50%)`
}

Now, we can assign the color to the ellipse element in createVisual.

const color = this.getColor(graph, port)
ellipseElement.setAttribute('fill', color)

Note	Remove or create edges to observe how the color of the port changes dynamically. The nodes in the corners have the color defined in the tag and therefore do not change dynamically.

The color also has to be considered in updateVisual. We add the color in the cache and update the fill property if the color has changed.

// get the graph from the render context
const graph = (context.canvasComponent as GraphComponent).graph
const color = this.getColor(graph, port)
if (cache.color !== color) {
  ellipseElement.setAttribute('fill', color)
  cache.color = color
}

Note	You can also use business data that’s stored in the port’s tag for conditional styling. This way, a single style instance that’s shared between all ports can produce varying visualizations.

05 Hit-Testing