Screen-based Hotspot detection

This script causes Hotspots to be detected based on their position on-screen, as opposed to being based on the cursor or Player character's position. This is similar to the system used by Beyond A Steel Sky, where the Hotspot closest to the centre of an invisible circle on the screen is the one selected.

To use it:

1. In the Settings Manager, set your "Hotspot detection method" to "Custom Script".
2. Copy the script below into a new C# file named ScreenHotspotDetection.cs
3. Create a new GameObject in the scene, and attach the new Screen Hotspot Detection component.
4. Set its Inspector's "Normal Max Depth" field, which is how far a way a Hotspot can normally be detected from, as desired
5. Optionally, assign icon textures in the Inspector, which will display when nearby Hotspots are detected
6. To override the "Normal Max Depth", and have a Hotspot be detect-able from far away, define an Interactive Boundary for that Hotspot.

ScreenHotspotDetection.cs:

```
using System.Collections.Generic;

using UnityEngine;

using AC;

public class ScreenHotspotDetection : MonoBehaviour

{

	public float normalMaxDepth = 2f;

	public Texture2D nearbyIcon = null;

	public Texture2D nearesetIcon = null;

	public float iconSize = 0.025f;

	private bool cameraIsActive;

	private List<Hotspot> nearbyHotspots = new List<Hotspot>();

	private Hotspot nearestHotspot;

	private Vector2 screenCircleCentre = new Vector2 (0.7f, 0.5f);

	private const float screenCircleRadius = 0.3f;

	private void Update ()

	{

		nearbyHotspots.Clear ();

		nearestHotspot = null;

		if (KickStarter.stateHandler.IsInGameplay ())

		{

				float nearestHotspotDistance = Mathf.Infinity;

				foreach (Hotspot hotspot in KickStarter.stateHandler.Hotspots)

				{

					Vector3 worldPosition = hotspot.GetIconPosition ();

					if (Vector3.Distance (KickStarter.player.transform.position, worldPosition) > normalMaxDepth)

					{

						if (hotspot.interactiveBoundary == null || !hotspot.interactiveBoundary.PlayerIsPresent)

						{

							continue;

						}

					}

				Vector3 viewportPosition = KickStarter.CameraMain.WorldToViewportPoint (worldPosition);

				if (viewportPosition.z < 0f) continue;

				float thisHotspotDistance = Vector2.Distance (viewportPosition, screenCircleCentre);

				if (thisHotspotDistance > screenCircleRadius)

				{

					nearbyHotspots.Add (hotspot);

					continue;

				}

				if (thisHotspotDistance < nearestHotspotDistance)

				{

					if (nearestHotspot)

					{

						nearbyHotspots.Add (nearestHotspot);

					}

					nearestHotspot = hotspot;

					nearestHotspotDistance = thisHotspotDistance;

				}

				else

				{

					nearbyHotspots.Add (hotspot);

				}

			}

			KickStarter.playerInteraction.SetActiveHotspot (nearestHotspot);

		}

	}

	private void OnGUI ()

	{

		if (nearestIcon != null && nearestHotspot)

		{

			GUI.DrawTexture (AdvGame.GUIBox (nearestHotspot.GetIconScreenPosition (), iconSize), nearesetIcon, ScaleMode.ScaleToFit, true, 0f);

		}

		if (nearbyIcon != null)

		{

			foreach (Hotspot hotspot in nearbyHotspots)

			{

				GUI.DrawTexture (AdvGame.GUIBox (hotspot.GetIconScreenPosition(), iconSize), nearbyIcon, ScaleMode.ScaleToFit, true, 0f);

			}

		}

	}

}

```