What does this unit3d C # code mean?

Question

Ray mouseRay = Camera.main.ScreenPointToRay(Input.mousePosition);
Vector3 newDotPosition =
    mouseRay.origin - mouseRay.direction / mouseRay.direction.y * mouseRay.origin.y;

I see that newDotPosition is the position of the game object on Terrain. But what does the following code do?

mouseRay.direction / mouseRay.direction.y * mouseRay.origin.y

Answer 1

In fact, this is some kind of basic geometry.

mouseRay.origin- camera position. Thus, mouseRay.origin.yis the height of the camera.

The result mouseRay.direction / mouseRay.direction.y * mouseRay.origin.yis the red vector in the image below. It just scales mouseRay.directionall the way across the earth.

Then he does mouseRay.origin - resultto get the point of impact on the earth in world coordinates.

And here is the code to see the result, if anyone is interested.

public class Test : MonoBehaviour
{
    public float originGizmoRadius = 1f;
    public float newDotPositionGizmoSize = 0.5f;
    public float directionLength = 2f;

    Vector3 origin;
    Vector3 direction;
    Vector3 newDotPosition;

    void Update()
    {
        Ray mouseRay = Camera.main.ScreenPointToRay(Input.mousePosition);

        origin = mouseRay.origin;
        direction = mouseRay.direction;

        newDotPosition = origin - direction / direction.y * origin.y;
    }

    void OnDrawGizmos()
    {
        Gizmos.color = Color.red;
        Gizmos.DrawSphere(origin, originGizmoRadius);
        Gizmos.DrawLine(origin, origin + (direction.normalized * directionLength));

        Gizmos.color = Color.green;
        Gizmos.DrawCube(newDotPosition, newDotPositionGizmoSize * Vector3.one);
    }
}