I would like to rotate an object to match its ground. So i cast 3 Rays (at the corners) to calculate the normal of the plane below. Now i need to rotate the object accordingly but keep the y rotation (so in which direction it "faces") so just setting transform.up = normal does not work. I thought i could just use the dot product between the transform directions to rotate it (so xRotation = Vector3.Dot(normal, transform.forward) for x and zRotation = Vector3.Dot(normal, transform.right) for z) this should be the angles between the normal vector and the right/forward vector. But as the result my object just faces the sky that way to the idea is completely wrong. Do you know how i should proceed ?

CodePudding user response：

Here is the solution to your problem. Although there are different methods for doing this, I personally find it best to use the Cross axis. In fact, you need Vector3.Cross instead of Vector3.Dot. This code works in such a way that by multiplying the transform.right of the player on the Ground normal vector, Since this axis calculates the perpendicular direction, you can expect it to give a forward corresponding to the ground.

public LayerMask groundLayer; // The Layer Ground
public Vector3 offset = Vector3.up;

private void Update()
{
    if (Physics.Raycast(transform.position, Vector3.down, out var groundHit, 2f, groundLayer.value))
    {
        var cross = Vector3.Cross(transform.right, groundHit.normal);

        var _lookRotation = Quaternion.LookRotation(cross, groundHit.normal);

        transform.position = groundHit.point   offset; // the offset is OPTIONAL, you can adjust it manuel or remove

        transform.rotation = _lookRotation;
    }   
}

Result:

You can see the result below. Consider that you can delete the offset code and make it compatible with the ground with mechanisms such as CharacterController or Rigidbody.