Easy See is an easy to use, scalable package, you can use it to easily see objects within the visual field (set objects tag), the field of vision can define your own, you can set the distance, angle and direction.
Unity WebGL & Document
You can set any object, including 2d and 3d scenes, you can add one or more objects.
Visual editor, easy-defined vision.
When you can see the object when you can add some event.