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I am working on a game project on unity and I am stuck at a camera problem

It has two camera angles. First person for engaging gameplay and top-down for 2D game experience. But in top down camera view I can't figure out the rotation of the camera with respect to player.
I wrote the following script for the main(top-down) camera view.
public class FollowPlayer : MonoBehaviour
{
public GameObject player;
private Vector3 offset = new Vector3(0f, 24.953f, -0f);
// Start is called before the first frame update
void Start()
{
}
// Update is called once per frame
void LateUpdate()
{
transform.position = player.transform.position + offset;
}
}`
I tried
transform.rotation = player.transform.rotation;
but it didn't work since camera is on top of player. If I could somehow do
transform.rotation = player.transform.rotation + X axis 90 degree;
That would be perfect but I don't know how to do that.

If I understand you correctly, you want to follow the player from above with your second camera. Leaving some flexibility, the best option I think would be Unity's built in Transform.LookAt(target) method (LookAt), which automatically rotates an object (in your case the camera) so that it faces the target.
Therefore, you could do something like this in your Update, assuming your script is attached to the Camera. Otherwise substitute transform with Camera.main.transform:
transform.LookAt(player);
Note: If you plan to have your camera fixed above your player at all times, it is sufficient if you perform the LookAt once, e.g. in Start and then attach the camera as a child to the player. If your camera does not move with your player in the world but you want it to focus the player anyway, do do it in Update. Hope I addressed your problem:)

My problem has been resolved. I was trying to rotate the wrong axis. My bad.
mouseInput = Input.GetAxis("Mouse X");
transform.Rotate(Vector3.forward * speed * -mouseInput);
I needed to get mouse input from user and change the Z-axis according to it. Game is working fine now.

Make GameObject's Y Rotation be the same as the camera's

I have a Cinemachine Freelook camera and i want it similar to Skyrim, where the character's rotation follows where the camera is pointing, but only on the Y axis so that i can move my mouse and look at the character from up and down;
This video demonstrates how MrKrabs can move in 3 dimensions, but won't turn.
I already tried creating a blank object and putting it at the center of the character, then using transform.LookAt(Camera) to make it point to where the camera is, and finally getting the Y value of the object's rotation, inverting it with -transform.position.y and applying it to MrKrabs, but it didn't work: it was jittery and overall just a bad user experience, is there a way to turn the gameobject based on the camera's rotation? (having the camera always watching his back)

Something like this should do the trick.
transform.rotation = Quaternion.Euler(0, Camera.main.transform.eulerAngles.y, 0);
Beware that if your camera is a child of your object it will rotate with it.

Unity Sub Camera following Player with rotation problem

Here is an image of what I'm trying to achieve
As you can tell it's a split screen game, the player is on the left, computer on the right.
there are 3 cameras in the game, main and two player cameras
the player camera MUST be independent of the player and CAN NOT be a child object of the player object, because the ball bounces and rotates while moving, the cameras must not.
when the balls change direction the camera must remain behind the player so the visual appears to show the landscape rotating with the player.
I've searched high and low for anything to put me on the right path but nothing seems to work right.
It should be a smooth transition so lerp and slerp are to slow for instant moving. I know LateUpdate will help with this.
If anyone can point me in the right direction I'd appreciate it.
Many thanks,
Paul

Have a script which takes in an object's position, in this case the player's ball, so you can code the camera as if it was a child of the object.
An simple example code for having a following camera would be something like...
FollowObject.cs
public Transform exampleObject;
private int offset = 5; //How far back the camera will be
void LateUpdate()
{
transform.position = new Vector3(exampleObject.transform.position.x,
exampleObject.transform.position.y,
exampleObject.transform.position.z - offset)
}

Control player z axis with mouse x axis

I'm trying to move the player to the position of the mouse in my game.
Right now movement along the x axis works fine, but I want the mouse y axis to control the characters movement along the z axis (because of my top-down camera's y being world z).
Right now mouse y controls player y, which looks like this in game.
And the code for it looks like this:
public Vector2 mousePos;
private Vector3 playerPos;
void update()
{
// Get mouse position from player
mousePos = Input.mousePosition;
// Move player with mouse
playerPos = new Vector3(mousePos.x, 0, mousePos.y);
transform.position = Camera.main.ScreenToWorldPoint(playerPos);
}
I then tried to just swap the y and z like this
playerPos = new Vector3(mousePos.x, mousePos.y, 0);
But instead of allowing me to control the z axis this snippet instead causes the player to lose all movement.
I'm very new to coding so I might be missing something completely obvious. What am I doing wrong?
Unity version: 2018.4.21f1

The example you gave isn't working because you're providing a z coordinate of 0 and when called on a perspective camera, Camera.ScreenToWorldPoint does some vector math, so in your scene view, your player is probably floating right on top of your camera. I can't explain the actual math because I don't understand it, but luckily for both of us, we don't need to! Essentially, the z coordinate is saying how far away from the camera to place the point, and since the view frustum of a perspective camera gets narrower closer to the camera, placing it at 0 means there's nowhere for it to go. how moving the object farther from the camera requires it to move farther to match the mouse position.
The bigger problem is that your method is wrong and there's a better way. Camera.ScreenToWorldPoint converts a mouse coordinate to a world space coordinate depending on what the camera is looking at, so you're essentially flippng the y and z coordinate, then feeding it into a method that figures out what coordinates need to be flipped.
It looks like this script is attached to your player gameObject, so it should look like this:
Camera cam;
[Range(1,10)] //this just creates a slider in the inspector
public int distanceFromCamera;
void Start()
{
//calling Camera.main is a shortcut for
//FindGameObjectsWithTag("MainCamera")
//so you should avoid calling it every frame
cam = Camera.main;
}
void Update()
{
//This will work for both perspective and orthographic cameras
transform.position = cam.ScreenToWorldPoint(
Input.mousePosition + new Vector3(0,0,distanceFromCamera));
}
If your camera is going to move closer or farther from the plane, make sure to add something that keeps the distance from camera updated.
That said, for most games having the player tied to the mouse cursor isn't usually what you're looking for. Generally you want some kind of input to move the player in some direction a certain amount. If that's what you're looking for, this part of the space shooter tutorial is a good introduction to player movement (though the code itself may be outdated).

How to drop a box to the mouse position?

I am trying to learn unity, and made my first own game and stucked at the beginning. The first idea was to drop a box (cube) to the mouse position. There are many videos and posts about getting the mouse position, and i tried to use them. My problem is, the mouse position i got is the camera's position, instead of the plane.
As you can see, it is kinda works, but it isn't fall to the plane.
https://prnt.sc/lmrmcl
My code:
void Update()
{
Wall();
}
void Wall()
{
if (Input.GetMouseButtonDown(0))
{
if (Input.GetMouseButtonDown(0))
{
wall = GameObject.CreatePrimitive(PrimitiveType.Cube);
Rigidbody wallsRigidbody = wall.AddComponent<Rigidbody>();
wall.transform.localScale = new Vector3(0.6f, 0.6f, 0.6f);
wallsRigidbody.mass = 1f;
wallsRigidbody.angularDrag = 0.05f;
wallsRigidbody.useGravity = true;
wallsRigidbody.constraints = RigidbodyConstraints.FreezeRotation;
wall.transform.position = Camera.main.ScreenToWorldPoint(Input.mousePosition);
}
Debug.Log(Camera.main.ScreenToWorldPoint(Input.mousePosition));
BoxCollider wallsCollider = wall.AddComponent<BoxCollider>();
wallsCollider.size = new Vector3(1f, 1f, 1f);
}
}
How should i change my code to get the right position?

This isn't a direct answer to your question, but I'm hoping it'll still get you where you need to go.
Prefabs are your friends! I'd highly recommend leveraging them here instead of constructing a cube directly in code.
But first, make sure everything else is set up right. Go ahead and construct a cube by hand in the Editor and make sure that when you hit Play, it falls as you expect. It should, provided it has a Rigidbody, collider, and you have gravity enabled (true by default).
If that works, drag that cube from your Hierarchy view into a folder in the Project view. This creates a prefab. You can now delete the cube from the Hierarchy view.
Update your script to have a public GameObject field, e.g.
public GameObject cubeToCreate;
Then, in the Inspector pane for whatever gameobject has that script attached, you should get a new field, "Cube To Create". Drag your prefab cube into that slot.
Lastly...update your code to wall = Instantiate(cubeToCreate). You'll still need to update the position, but you should be able to drop the rest of the initialization logic you have above, e.g. setting mass and drag.
As for the actual problem, the first thing that concerns me is how do you plan on turning a 2d mouse click into a 3d point? For the axis going "into" the screen...how should the game determine the value for that?
Camera.main.ScreenToWorldPoint accepts a Vector3, but you're passing it a Vector2 (Input.mousePosition, which gets converted to a z=0 Vector3), so the point is 0 units from the camera -- so in a plane that intersects with the camera.
I haven't done this, but I think you'll need to do raycasting of some sort. Maybe create an invisible 2d plane with a collider on it, and cast a physics ray from the camera, and wherever it hits that plane, that's the point where you want to create your cube. This post has a couple hints, though it's geared toward 2D. That might all be overkill, too -- if you create a new Vector3 and initialize it with your mouse position, you can set the z coordinate to whatever you want, but then your cube creation will be in terms of distance from the camera, which is not the best idea.
Hope this helps.