Unity C# Scale 2d Object with Mouse Drag

Question

So I have had a few attempts and posts about this but have still not been successful. The behaviour I want is this:

There is a circle (sphere) I want the player to be able to click and drag it outwards to make it larger, or drag inwards to make it smaller. Previously, I was scaling the object based on the inital dragging point, but this was giving me no way to scale the shape back down.. only make it larger. I figured I need to calculate whether we should be scaling up or down, based on the direction of the drag in relation to the centre of the shape. To figure this out, we need to check the position of the mouse, while dragging, compare it to the previous frame and decide whether we are closer or further away from the centre. If we are closer, then we are dragging inwards and we should scale the object down (make it smaller). Id we are further away, then we are moving outwards and should be scaling up (make it larger). I'm having a couple of problems. I don't seem to be able to get the circle to scale down at all. The detection for the direction of the drag seems to be flawed as it seems my bool for isDraggingOut is basically always true, I can't understand why. The other problem I'm having is that every time I click the circle, it snaps back to it's initial size.

I am trying to take the following steps in my code:

On Mouse drag: check where current position of the mouse is

check distance of previous position of the mouse

check distance of current position

determine whether player is dragging in or out. If current distance is more than the distance in the previous frame, we are dragging out

If this is true, then calculate the distance between the drag start point and the current position of the mouse, and scale accordingly

If the distance is less than the previous frame then we are dragging in

then calculate the distance between the drag start point and the current position of the mouse, and scale accordingly (here, i have tried to apply an inverse calculation of the upscaling calculation - this could be wrong)

The last thing I do in my code is make the current position equal to previousPosition variable, so that in the next frame it can be compared.

Any help would be appreciated as I am really struggling with this one.

---

using System.Collections.Generic;

using UnityEngine;

public class NewScalingScript : MonoBehaviour

{

public Vector3 temp;
public Vector3 dragStartingPoint;
public Vector3 centreOfShape;
public Vector3 currentDragPosition;
public Vector3 previousDragPosition;
public bool isDraggingOut;
public float previousDistance;
public float currentDistance;
public float amountDragged;
public float clampedAmountDragged;
private void Awake()

{

    centreOfShape = transform.position;

}

private void OnMouseDown()

{

    dragStartingPoint = Input.mousePosition;

}

private void OnMouseDrag()

{

//check where current position is

    currentDragPosition = (Input.mousePosition);

//check distance of previous position

    previousDistance = Vector3.Distance(previousDragPosition, centreOfShape);

//check distance of current position

    currentDistance = Vector3.Distance(currentDragPosition, centreOfShape);

//determine whether player is dragging in or out. If current distance is

// more than the distance in the previous frame, we are dragging out

if (currentDistance > previousDistance)

{

        isDraggingOut = true;

}

else

{

        isDraggingOut = false;

}

if (isDraggingOut == true)

{

       amountDragged = Vector3.Distance(currentDragPosition, dragStartingPoint);

// set minimum and maximum drag amount and store in clampedAmountDragged variable

        clampedAmountDragged = Mathf.Clamp(amountDragged, 100f, 300f);

// set amountDragged to clampedAmount to apply minimum and maximum

        amountDragged = clampedAmountDragged;

        temp = transform.localScale;

        temp.x = amountDragged / 100;

        temp.y = amountDragged / 100;

//make scale of object equal to temp variable

        transform.localScale = temp;

}

// else we are dragging in

else if (isDraggingOut == false)

{

        amountDragged = Vector3.Distance(currentDragPosition, dragStartingPoint);

// set minimum and maximum drag amount and store in clampedAmountDragged variable

        clampedAmountDragged = Mathf.Clamp(amountDragged, 100f, 300f);

// set amountDragged to clampedAmount to apply minimum and maximum

        amountDragged = clampedAmountDragged;

        amountDragged = amountDragged - 300;

        amountDragged = Mathf.Abs(amountDragged);

        temp = transform.localScale;

        temp.x = amountDragged / 100;

        temp.y = amountDragged / 100;

 //make scale of object equal to temp variable

        transform.localScale = temp;

}

   currentDragPosition = previousDragPosition;

}

}

Answer 1

I think I can explain your problem.

When you let go of the mouse, that spot basically becomes "point a", and when you go back to the circle and click on it, it creates "point b". As the distance between those two points has a negative value (think of an x/y graph), the program is automatically shrinking the ball back down. It's less like the ball is snapping back to normal size and more like it's shrinking down in practically a millisecond.

At least, that's what I can gleam from this. I could very well be wrong about it.

EDIT: Actually, perhaps it's more like the program is setting "point b" as the new "point a", and since the distance between them is relatively small, that's what's making the ball shrink, because the distance between those two points is what dictates the size of the ball.

Answer 2

You are defining currentDragPosition and dragStartingPoint properly, but you have neglected to actually define previousDragPosition other than declaring it as a variable. At the very least in OnMouseDown() after you put

dragStartingPoint = Input.mousePosition; 

add the line

previousDragPosition = dragStartingPoint;

to give previousDragPosition some sort of meaningful value.