Calculate point in world space out of cameras view [2D]

Unity Engine
1

Hi I have a script that should find point in 2D world space that is not visible from main camera. For example (red):

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using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class SpawnCamera : MonoBehaviour
{

    private GameObject cam;
    public GameObject prefab;
    private Vector3 playerObjectLocation = new Vector3(0, 0, 0);

    // Start is called before the first frame update
    void Start()
    {
        cam = GameObject.FindGameObjectWithTag("MainCamera");
        InvokeRepeating("spawnEnemy", 2.0f, 1.0f);

    }

    private Vector3 getCornerWorldCoords()
    {
        Vector3 pos = cam.GetComponent<Camera>().ScreenToWorldPoint(new Vector3(0, 0, 1));
        pos[2] = 0;
        return pos;
    }

    private float calculateDistance()
    {
        Vector3 cornerPosition = getCornerWorldCoords();
        float sq_x = Mathf.Pow(cornerPosition[0] - playerObjectLocation[0], 2);
        float sq_y = Mathf.Pow(cornerPosition[1] - playerObjectLocation[1], 2);
        return Mathf.Sqrt(sq_x + sq_y);
    }

    private Vector3 getSpawnPointOutOfCameraWithRandomAngle(float lengthFactor = 1.0f)
    {
        float radius = calculateDistance() * lengthFactor;
        float angle = Random.Range(0, 360);
        float x = radius * Mathf.Sin(Mathf.PI * 2 * angle / 360);
        float y = radius * Mathf.Cos(Mathf.PI * 2 * angle / 360);
        return new Vector3(x, y, 0);

    }

    private void spawnEnemy()
    {
        Vector3 spawnPoint = getSpawnPointOutOfCameraWithRandomAngle();
        //Vector3 pos = Camera.main.ScreenToWorldPoint();
        //Debug.Log(pos);
        GameObject.Instantiate(prefab, spawnPoint, cam.transform.rotation, null);
    }

    // Update is called once per frame
    void Update()
    {

    }
}

I assume that bottom left corner is point (0, 0) in camera view. I get world position of point (0, 0), and then calculate distance between center of world grid and corner (multipled by float to determine how far from screen border should object be spawned). Then I calculate point on circle which should be out of camera view or should be one of the corners of screen. But when I instantiate prefab it is spawned on black circle.

Does anyone see any issue in this script, that make this script instantiate objects to close to center?
Thanks.

2

Are using a perspective camera? If so, then your black circle is the correct radius, but because it is in front of the camera (because you set its z value to 0), it is visible (and, so, smaller in screen space).

In getCornerWorldCoords(), why do you change the result’s z coordinate to 0? Similarly, on line 41, why are you setting the z coordinate of your result to 0? This is what pushes your circle away from the camera, making it visible.

If you get the real point of the bottom left of the screen in world space, unmodified, you can construct a ray from the camera position to that point. Intersect the ray with the a plane (e.g. “new Plane(Vector.zero, Vector.back)”, assuming the player is at (0, 0, 0)), then I think that the intersection will be the desired spawn point.

You have to think about the fact that the view volume is a frustum (truncated pyramid). The circle you are using to spawn objects on is an intersection of a cone that contains the frustum. But it is the wrong diameter for z = 0. It is the correct diameter for Z at the frustum’s near plane (I think that’s how ScreenToWorldPoint() works – you should double check). But you are pushing it away, without enlarging it, so it’s not the right diameter anymore. A ray will travel along the surface of the cone, giving you the correct diameter at any distance from the camera that you ask it for.