object orientation placement schemes

.LetsRotateAndSpawn.cs.md

LetsRotateAndSpawn.cs

// src* = https://gist.github.com/andrew-raphael-lukasik/49db89424f11d3edd937c536e5b41d54
using UnityEngine;

public class LetsRotateAndSpawn : MonoBehaviour
{
	[SerializeField] GameObject _prefab = null, _prefabPreview = null;
	[SerializeField] Vector3 _planeOrigin = Vector3.zero , _planeNormal = Vector3.up;
	GameObject _instancePreview = null;
	Vector3 _cursorPos = Vector3.zero, _cursorDragPosStart = Vector3.zero;
	Quaternion _cursorRot = Quaternion.identity, _cursorDragRotStart = Quaternion.identity;
	Camera    _camera = null;
	void Start ()
	{
		_camera = Camera.main;
		_instancePreview = GameObject.Instantiate( _prefabPreview );
		_instancePreview.SetActive( false );
	}
	void Update ()
	{
		Plane plane = new Plane( inNormal:_planeNormal , inPoint:_planeOrigin );
		var ray = _camera.ScreenPointToRay( Input.mousePosition );
		if( plane.Raycast( ray , out var hitDist ) )
		{
			Vector3 hitPoint = ray.origin + ray.direction * hitDist;
			_cursorPos = hitPoint;

			// store rot pivot info
			if( Input.GetMouseButtonDown(1) )
			{
				_cursorDragPosStart = hitPoint;
				_cursorDragRotStart = _cursorRot;
			}
			
			// update rotation
			if( Input.GetMouseButton(1) )
			{
				Vector3 vec = _cursorPos - _cursorDragPosStart;
				float screenPxDist = Vector2.Distance( _camera.WorldToScreenPoint(_cursorDragPosStart) , _camera.WorldToScreenPoint(_cursorPos) );
				if( vec.sqrMagnitude>0 )
				_cursorRot = Quaternion.Slerp(
					_cursorDragRotStart ,
					Quaternion.LookRotation( vec , _planeNormal ) ,
					Mathf.SmoothStep( 0 , 1 , screenPxDist / ( Mathf.Min(Screen.width,Screen.height) * 0.05f ) )
				);
			}

			// update preview mesh
			if( !_instancePreview.activeSelf ) _instancePreview.SetActive( true );
			_instancePreview.transform.SetPositionAndRotation( hitPoint , _cursorRot );

			// spawn prefab
			if( Input.GetMouseButtonDown(0) )
				GameObject.Instantiate( _prefab , hitPoint , _cursorRot );
		}
		else _instancePreview.SetActive( false );
	}
	void OnDrawGizmos ()
	{
		if( _camera!=null && Input.GetMouseButton(1) )
		{
			Gizmos.color = Color.yellow;
			Vector3 offset = new Vector3{ z=_camera.nearClipPlane*2f };
			Gizmos.DrawLine(
				_camera.ScreenToWorldPoint( Vector3.Scale( _camera.WorldToScreenPoint(_cursorDragPosStart) , new Vector3{x=1,y=1} ) + offset ) ,
				_camera.ScreenToWorldPoint( Vector3.Scale( _camera.WorldToScreenPoint(_cursorPos) , new Vector3{x=1,y=1} ) + offset )
			);
		}
		Gizmos.matrix = Matrix4x4.TRS( _planeOrigin , Quaternion.AngleAxis(0,_planeNormal) , Vector3.one );
		Gizmos.DrawWireCube( Vector3.zero , new Vector3{ x=100 , z=100 } );
	}
}

LetsSpawnAndRotate.cs

// src* = https://gist.github.com/andrew-raphael-lukasik/49db89424f11d3edd937c536e5b41d54
using UnityEngine;

public class LetsSpawnAndRotate : MonoBehaviour
{
	[SerializeField] GameObject _prefab = null, _prefabPreview = null;
	GameObject _instance = null;
	Vector3 _pos, _normal;
	Vector2 _click;
	void Update ()
	{
		var camera = Camera.main;
		var ray = camera.ScreenPointToRay( Input.mousePosition );

		if( Input.GetMouseButtonDown(0) )
		{
			if( Physics.Raycast(ray,out var hit) )
			{
				_pos = hit.point;
				_normal = hit.normal;
				_instance = GameObject.Instantiate(
					_prefabPreview ,
					_pos ,
					Quaternion.AngleAxis( 90 , Quaternion.LookRotation(_normal)*Vector3.right ) * Quaternion.LookRotation(_normal)
				);
				_click = Input.mousePosition;
			}
		}

		if( _instance!=null )
		{
			Vector2 mouseDelta = (Vector2) Input.mousePosition - _click;
			if( Physics.Raycast(ray,out var hit) && (mouseDelta).sqrMagnitude>0 )
			{
				float yaw = -Mathf.Atan2( mouseDelta.y , mouseDelta.x );
				Quaternion rotBase = Quaternion.AngleAxis( 90 , Quaternion.LookRotation(_normal)*Vector3.right ) * Quaternion.LookRotation(_normal);
				Quaternion rotAux = Quaternion.AngleAxis( Mathf.Rad2Deg*yaw , _normal );
				_instance.transform.rotation = rotAux * rotBase;
			}
			if( Input.GetMouseButtonUp(0) )
			{
				GameObject.Instantiate( _prefab , _instance.transform.position , _instance.transform.rotation );
				Destroy( _instance );
				_instance = null;
			}
		}
	}
	void OnDrawGizmos ()
	{
		Gizmos.DrawRay( _pos , _normal );
	}
}