Using Camera ViewportPointToRay (Unity)

z4gon
z4gon

Raycasting from the Camera and finding the hit point in a plane, to determine a surface area corresponding to the proyected view from the Camera on the Plane.

References

Table of Content

Using Raycast

The method ViewportPointToRay transforms a coordinate in viewport space (0,0) to (1,1) into a ray that starts from the corresponding point in the camera near clip plane and points into the direction coming from the camera transform position.

Using a trigger collider for a plane, you can raycast this ray and find the hit point in the surface.

This allows to generate a shape that corresponds to the camera view, proyected on a surface, even when the camera is tilted.

1private Camera mainCamera;
2private LayerMask raycastLayerMask;
3private float raycastMaxDistance = 40;
4private Transform[] corners;
5
6void Awake()
7{
8    PositionCorner(new Vector2(0.0f, 0.0f), corners[0]);
9    PositionCorner(new Vector2(1.0f, 1.0f), corners[1]);
10}
11
12private void PositionCorner(Vector2 viewportPoint, Transform corner)
13{
14    RaycastHit hit;
15    var ray = mainCamera.ViewportPointToRay(points[i]);
16    if (
17        Physics.Raycast(
18            ray,
19            out hit,
20            raycastMaxDistance,
21            raycastLayerMask,
22            QueryTriggerInteraction.Collide
23        )
24    )
25    {
26        corner.transform.position = hit.point;
27    }
28}

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Drawing Gizmos

The gizmos are useful for visualizing the area shape.

1void OnDrawGizmos()
2{
3    if (corners != null && corners.Length > 1)
4    {
5        var botLeft = corners[0].transform.position;
6        var botRight = new Vector3(-botLeft.x, botLeft.y, botLeft.z);
7        var topRight = corners[1].transform.position;
8        var topLeft = new Vector3(-topRight.x, topRight.y, topRight.z);
9
10        Gizmos.color = Color.yellow;
11
12        Gizmos.DrawLine(topLeft, topRight);
13        Gizmos.DrawLine(botLeft, botRight);
14        Gizmos.DrawLine(botLeft, topLeft);
15        Gizmos.DrawLine(botRight, topRight);
16    }
17}

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