transform. Forward and vector3 Differences in the use of forward

unity There are several direction vectors that can be used directly , Namely transform.forward,transform.up,transform.right and Vector3.forward,Vector3.up,Vector3.right.

In terms of numbers ,transform.forward,transform.up,transform.right Is the direction vector of the three axes in the game object's own coordinate system , and Vector3.forward,Vector3.up,Vector3.right Are the three axes of world coordinates .

But when transform.translate and transform.rotate When the function uses these vectors, you should pay attention to .

For example, we want an object to always move forward along its own coordinate system , Take it for granted that it will be written like this

 void Update()
{
        if(Input.GetKey(KeyCode.W))
            transform.Translate(transform.forward * Time.deltaTime * 1.0f);
}

But in this way, if the object coordinate system is inconsistent with the world coordinate , Moving in a strange direction , It is not along the axis of world coordinates or its own coordinates , The black tip in the figure below is the actual moving direction .

  How did this strange direction come from

  Pictured above , Set the blue arrow in its coordinate system as x1, The black arrow is y1, Rotate the object coordinate system so that it coincides with the world coordinates , that y1 It also rotates together to get the black arrow on the left y2, and y2 And x1 parallel , That is, the direction vector is the same , Push this process backward to get y1 Is the actual direction of movement . So clearly , This complex process and its results are not what we want .

actually ,translate and rotate These two functions can input coordinate system parameters , If it is not entered, the default value is space.self. If you want to move forward along your own coordinates, there are two ways to write , Rotating along its own coordinate system is the same

transform.translate(vector3.forward,Space.self) 
transform.translate(transform.forward,Space.world)