Unity3D Ui, Calculation for Position Dragging an Item

Unity3D UI, calculation for position dragging an item?

For Draging stuff I just do this :

using UnityEngine;
using UnityEngine.UI;
using UnityEngine.EventSystems;

public class Draggable : MonoBehaviour, IBeginDragHandler, IDragHandler, IEndDragHandler {
    
    
    
    public void OnBeginDrag(PointerEventData eventData) {
        
    }
    
    public void OnDrag(PointerEventData eventData) {
        //Debug.Log ("OnDrag");
        
        this.transform.position = eventData.position;

        }

    public void OnEndDrag(PointerEventData eventData) {
        Debug.Log ("OnEndDrag");
    
    }
}

Here's the identical amazing URIPOPOV CODE with two simple features which you always need when dragging:

// allow dragging with two basic problem fixes:
// - limit drag to the parent box
// - don't "jump" based on where you hold down

100% tested:

Note that you MUST USE the scale conversion code from #programmer below.

using UnityEngine;
using UnityEngine.EventSystems;

public class AmazingUPDrag : MonoBehaviour,
               IBeginDragHandler, IDragHandler, IEndDragHandler
{

RectTransform rt;
Vector2 dragOffset = Vector2.zero;
Vector2 limits = Vector2.zero;

Canvas canvas;

void Awake()
{
    rt = GetComponent<RectTransform>();
    canvas = GetComponentInParent<Canvas>();
}

public void OnBeginDrag(PointerEventData eventData)
{
    dragOffset = ActualPos(eventData.position) - (Vector2)transform.position;
    limits = transform.parent.GetComponent<RectTransform>().rect.max;

    limits.x = limits.x - 100f;
    limits.y = limits.y - 100f;
}

public void OnDrag(PointerEventData eventData)
{
    transform.position = ActualPos(eventData.position) - dragOffset;

    var p = transform.localPosition;
    if (p.x < -limits.x) { p.x = -limits.x; }
    if (p.x > limits.x) { p.x = limits.x; }
    if (p.y < -limits.y) { p.y = -limits.y; }
    if (p.y > limits.y) { p.y = limits.y; }
    transform.localPosition = p;
}

public void OnEndDrag(PointerEventData eventData)
{
    dragOffset = Vector2.zero;
}

Vector2 ActualPos(Vector2 unityDelusionPos)
{
    Vector2 p;
    RectTransformUtility.ScreenPointToLocalPointInRectangle(
        (RectTransform)(canvas.transform),
        unityDelusionPos,
        canvas.worldCamera,
        out p);
    return canvas.transform.TransformPoint(p);
}

}

Unity drag and drop in world positions

So after a bit of playing around and inspecting the various values I was receiving from the calls to ScreenToWorldPoint I finally tracked down the issue.
In the code for my second attempted approach I found that I was using an incorrect value for the Z argument in ScreenToWorldPoint. After doing a bit of research I found that his should be the Z distance between the camera and the (i guess) touch surface.

Vector3 screenCenter = new Vector3(Screen.width * 0.5f, Screen.height * 0.5f, -Camera.main.transform.position.z);
Vector3 screenTouch = screenCenter + new Vector3(eventData.delta.x, eventData.delta.y, 0);

Thanks to everyone who took the time to read through my question.

Dragging Item With Icon Following Pointer Unity C#

Very fortunately, there is now an

incredibly simple way

to do this in Unity.

Here it is: https://stackoverflow.com/a/37473953/294884

Ask if you have more trouble!

How to make Unity UI object draggable when the objects are instantiating at runtime?

At the time you Instantiate your GameObject obj, do:

obj.addComponent("YourScript");

where YourScript is your script, which you have written, that attached to a GameObjects makes it draggable..

Alternatively, you instantiate a prefab, attach the script to the prefab through the editor.

This is preferrable because addComponent() will get deprecated in the next versions.

I also recommend to keep a List<YourInstantiatedObjectType> in the parent.

Unity drag doesn't work, object moves away from the pointer

It's better to use Screen Space - Overlay if the camera's viewport is unchanged. Then following code will work:

this.transform.position = eventData.position;

To use Screen Space - Camera, you need transform the event position into the camera space:

Vector3 position = eventData.position;
var canvas = image.canvas;
position.z = canvas.planeDistance;
image.transform.position = canvas.worldCamera.ScreenToWorldPoint(position);

drag and drop in unity, drag behind other UI elements

Try adding a "Canvas" component to your prefab and check "override sorting" and set sort order. I think I also had to add a graphic raycaster.

Inspector:

Unity - How to calculate new position for an object from pitch of another object in 3D

Hotspots

If you'd like to place something at a particular location on a generic object which can be scaled or transformed anywhere, then a "hotspot" can be particularly useful.

What's a hotspot?

Edit the target gameobject (the line in this case) and add an empty gameobject to it. Give it some appropriate name - "cross arms hotspot" for example, and then move it to the location where you'd like your other gameobject to target. Essentially, a hotspot is just an empty gameobject - a placement marker of sorts.

How do I use it?

All you need is a reference to the hotspot gameobject. You could do this by adding a little script to the pole gameobject which tracks it for you:

public class PowerPole : MonoBehaviour {
    public GameObject CrossArmsHotspot; // Set this in the inspector
}

Then you can get that hotspot reference from any power pole instance like this:

var targetHotspot = aPowerPoleGameObject.GetComponent<PowerPole>().CrossArmsHotspot;

Then it's just a case of getting your target object to place itself where that hotspot is, using whichever technique you prefer. If you want it to just "stick" there, then:

void Start(){
   targetHotspot = aPowerPoleGameObject.GetComponent<PowerPole>().CrossArmsHotspot;
}

void Update(){
    transform.position = targetHotspot.transform.position;
}

would be a (simplfied) example.

A more advanced example using lerp to move towards the hotspot:

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class CrossArmsMover : MonoBehaviour
{
    public GameObject PowerPole;
    private GameObject targetHotspot;
    public GameObject CrossArms;
    public float TimeToTake = 5f;
    private float timeSoFar;
    private Vector3 startPosition;
    private Quaternion startRotation;

    // Start is called before the first frame update
    void Start()
    {
        startPosition = CrossArms.transform.position;
        startRotation = CrossArms.transform.rotation;
        targetHotspot = PowerPole.GetComponent<PowerPole>().CrossArmsHotspot;
    }

    // Update is called once per frame
    void Update()
    {
        timeSoFar+=Time.deltaTime;

        var progress = timeSoFar/TimeToTake;

        // Clamp it so it doesn't go above 1.
        if(progress > 1f){
            progress = 1f;
        }

        // Target position / rotation is..
        var targetPosition = targetHotspot.transform.position;
        var targetRotation = targetHotspot.transform.rotation;

        // Lerp towards that target transform:
        CrossArms.transform.position = Vector3.Lerp(startPosition, targetPosition, progress);
        CrossArms.transform.rotation = Quaternion.Lerp(startRotation, targetRotation, progress);

    }
}

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