How to limit where a sprite can move in Unity? - unity3d

Question

I am fairly new to Unity so please bear with me I have tried looking for the answer everywhere, but have had no luck.
Basically I am using onMouseDrag to move a sprite around the background for a classroom (1366x768) that has a table. However, I want to limit where the sprite can go so that it does not end up off screen or off of the table on my background.
My sprite has the 2d box collider and rigidbody components attached (gravity is set to zero and it is at a fixed angle). I thought that by placing four 2d box colliders around the area I want to keep the sprite in it would be enough to contain it but the sprite simply goes straight through them.
I also read up about using Mathf.Clamp to restrict the area but I do not really understand how to use it from the examples I have seen.
Below is my code for moving the sprite:
using UnityEngine;
using System.Collections;
public class MovementScript : MonoBehaviour {
float x;
float y;
void Update() {
x = Input.mousePosition.x;
y = Input.mousePosition.y;
}
public void OnMouseDrag() {
transform.position = Camera.main.ScreenToWorldPoint (new Vector3 (x, y, 1.0f));
}
}
Any help would be greatly appreciated!

Answer 1

Moving an object using its transform is not the same as moving it.
When you use the transform, the object doesn't "move", it teleports every Update by a small amount. Unfortunately, the Rigidbody can't detect this change in position as movement and thus does not react with any colliders. Regardless, that's probably the more complicated way to do this. Using Clamp is definitely easier.
Clamp is a pretty straightforward function. it takes three args: a value, a min, and a max. If the value is less than min or greater than max, it returns that boundary. Otherwise, it returns the value itself.
For instance,
Mathf.Clamp(5, 1, 3); //returns 3
Mathf.Clamp(2, 1, 3); //returns 2
Mathf.Clamp(-2, 1, 3); //returns 1
This is simply a convenience function for something like this:
if(val > max) {
return max;
} else if(val < min) {
return min;
} else {
return val;
}
So using Clamp, you can restrict the values of your x and y coordinates:
//to avoid confusion, I'm referring to your x and y variables
//as inputX and inputY. they represent the mouse position.
public void OnMouseDrag() {
Vector3 pos = Vector3.zero;
pos.x = Mathf.Clamp(inputX, minX, maxX);
pos.y = Mathf.Clamp(inputY, minY, maxY);
pos.z = 1.0;
transform.position = Camera.main.ScreenToWorldPoint (pos);
}
Mathf.Clamp will keep the X and Y coordinates of your Transform within the range (minX, maxX) and (minY, maxY) respectively. You can create these variables as inspector variables so you can change them on the fly.