screenspace to worldspace, not working

Questions & Answers
1

I am trying to make a mouse trail. When you move your mouse, the gameobject with trail renderer will move along with your mouse. So I first got mouse position which is on screenspace. Then I converted it to worldspace. Then I put the converted position onto trail’s position. But it is not working. When I place my mouse on bottom-left corner of screen, only then the trail comes.But it comes at the middle of screen! And if I move mouse by very few pixels, the trail move by large pixels(often out of screen!)
The code I am using is below:

using UnityEngine;
using System.Collections;

public class debugGUIscript : MonoBehaviour
{
public Transform trail;
public Camera camera;
  void Update()
    {
     Matrix4x4 conv=camera.cameraToWorldMatrix;
     Vector3 convMousePoint= conv.MultiplyPoint(new Vector3(Input.mousePosition.x,Input.mousePosition.y,0.0f));
trail.transform.position= new Vector3 (convMousePoint.x,convMousePoint.y, 0.0f); 
    }
}

What is the problem of my script?

2

screen to world method, “Camera.ScreenToWorldPoint”. You are referring this,right? Oh boy, thank you very very much. Now I have got it right. For anyone facing similar situation, The changed code for mouse trail is:

 using UnityEngine;
        using System.Collections;
         
        public class debugGUIscript : MonoBehaviour
        {
        public Transform trail;
        public Camera camera;
        void Update()
        {
    Vector3 convMSpoint= camera.ScreenToWorldPoint(new Vector3(Input.mousePosition.x, Input.mousePosition.y, camera.nearClipPlane));
    trail.transform.position= new Vector3(convMSpoint.x,convMSpoint.y,convMSpoint.z);
        }
        }

There should be a gameObject with which a trail renderer attached. At first,trail might go to a very biger size. So, we should carefully put nice value on “time” “start width” “end width” “min vertex distance”.

I guess we can transform any gameobject into screen by this method,isn’t it? Using “Camera.ScreenToWorldPoint” and “Camera.WorldToScreenPoint” with a second depth enabled camera could lead to a nice GUI system with minimal drawcall.

edit I have successfully converted it for touch too. Here is the code for touch devices.

using UnityEngine;
using System.Collections;

public class debugGUIscript : MonoBehaviour
{
	public Transform trail;
	public Camera camera;
	
	void Update()
	{
        foreach (Touch touch in Input.touches) 
		{
		Vector3 convTCpoint= camera.ScreenToWorldPoint(new Vector3(touch.position.x, touch.position.y, camera.nearClipPlane));
		trail.transform.position= new Vector3(convTCpoint.x, convTCpoint.y,convTCpoint.z);
                }
        }
}