07 Hit-Testing Demo - yFiles for HTML

Customizing hit-testing

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 NodeStyleBase class only considers the node layout when hit-testing. When nodes have shapes that deviate from the rectangular node layout, hit-testing has to be adjusted by providing a different implementation for the isHit method.

In this example, we have to exclude the upper-right corner 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,
  node: INode
): boolean {
  // Check for bounding box
  if (!node.layout.toRect().contains(location, context.hitTestRadius)) {
    return false
  }
  const { x, y } = location
  const { x: layoutX, y: layoutY } = node.layout

  // Check for the upper-right corner, which is empty
  if (
    x > layoutX + tabWidth + context.hitTestRadius &&
    y < layoutY + tabHeight - context.hitTestRadius
  ) {
    return false
  }
  // all other points are either inside the tab or the rest of the node
  return true
}

Note	Try this implementation by hovering both nodes. Notice that the red node, which uses the default hit-test, also detects hits in the upper right, empty corner. The blue node uses the adjusted hit-test code.