Styles not only provide a visual representation for graph items. They also offer crucial parts for interacting with said items. Hit-testing determines whether a particular item is at a given point in the canvas. It happens all the time during interaction, e.g., when selecting items, moving nodes, or creating edges.
The default implementation in the EdgeStyleBase class only considers
the polyline with thickness 1.0 when hit-testing. When edges have shapes
that deviate from the polyline, hit-testing has to be adjusted by providing a
different implementation for the isHit method.
In this example, we have to include the thickness of the edge visualization for the hit-test. We also take the hit-test radius into account. This radius enables a bit of fuzziness when hit-testing the item, so you can still hit it when you’re slightly outside.
protected isHit(
context: IInputModeContext,
location: Point,
edge: IEdge
): boolean {
const thickness = this.distance + 2
const edgePath = super.getPath(edge)!
return edgePath.pathContains(
location,
context.hitTestRadius + thickness * 0.5
)
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Note
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Try this implementation by hovering both edges. Notice that the left edge, which uses the default hit-test, only detects hits in the center of the edge visualization. The right edge uses the adjusted hit-test code. |