Get the screen diagonal length in world units

Unity Engine
1

I’m trying to calculate the screen diagonal length in world units.
I’ve tried this but it doesn’t seem to work.

Camera.main.ScreenToWorldPoint(new Vector2(Screen.width, Screen.height)).magnitude

Any help would be appreciated.

2

Try:

Camera camera = Camera.main;

float magnitude = camera.ScreenToWorldPoint(new Vector3(camera.pixelWidth, camera.pixelHeight, camera.nearClipPlane)).magnitude;
1 Like
3

I think @GroZZleR 's answer depends on the camera position and will only be correct if the lower-left corner of the near-clip plane happens to be at the origin. Basically, you’re computing the distance from the origin to the upper-right corner of the near-clip plane.

To do it generally, you’d need two ScreenToWorldPoint calls to get the lower-left and upper-right corners and then take the magnitude of the difference between those points.

But I think it’s easier to do it with some trigonometry:

// For orthographic mode, it only depends on the orthographic size:
var height = camera.orthographicSize * 2f;
var width = height * camera.aspect;

// For perspective mode, it depends on the field of view and the desired distance from the camera:
var height = Mathf.Tan(0.5f * camera.fieldOfView * Mathf.Deg2Rad) * distance * 2f;
var width = height * camera.aspect;

// Then the diagonal is:
var diagonal = Mathf.Sqrt(height * height + width * width);
3 Likes
4

Thank you so much for this answer, I am using a 2d orthographic camera which at point (0, 0), so I just needed to multiply the value of the expression I posted by 2. Thank you for clearing this up.