c# - 这个 unity3d c# 代码是什么意思？

Question

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

我看到 newDotPosition 是游戏对象在地形上的位置。但是下面的代码是做什么的呢？

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

Answer 1

其实就是一些基本的几何学。

mouseRay.origin 是相机的世界位置。所以 mouseRay.origin.y 是相机的高度。

mouseRay.direction/mouseRay.direction.y * mouseRay.origin.y 的结果是下图中的红色矢量。它只是在地面上一直缩放 mouseRay.direction。

然后它执行 mouseRay.origin - result 以在世界坐标中获取地面上的命中点。

如果有人感兴趣，这里是查看结果的代码。

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);
    }
}