Piece of code to convert from world space size to pixel size. Handy if you need to fit something to a pixel sized displayed area in a UI.

All you need is to supply the size of the object in world space and the distance from the camera to the object.

private Vector2 GetSizeAtDepth(Vector2 a_size, float a_depth, Camera a_camera)
{
    float fov2 = a_camera.fieldOfView * Mathf.PI / 360.0f;
    float height = Mathf.Tan(fov2) * a_depth * 2.0f;

    float pixelHeight = (a_size.y / height) * Screen.height;
    float pixelWidth = (a_size.x / (height * a_camera.aspect)) * Screen.width;

    return new Vector2(pixelWidth, pixelHeight);
}

Call it with something like the code below and it’ll return pixel sizes using the current screen res.

float depth = 8.0f;
Vector2 res = GetSizeAtDepth(new Vector2(10.0f, 10.0f), depth, m_renderCamera);

Debug.Log("pixelWidth: " + res.x);
Debug.Log("pixelHeight: " + res.y);

So, this is passing in a 10 x 10 x/y as the world space size (size of a standard Unity plane).

The ‘depth’ is the distance from the camera to the object. As the object is a plane that’s facing the camera, we don’t need to find a specific depth within the object. i.e. if it was a sphere then we’d have to decide if we wanted depth to the front, middle or back.

m_renderCamera is just a standard Unity camera.

Obviously, this can easily be adapted to work without Unity but I’m using it to get something up and running quickly.

Hope it helps!