Convert Unity UI Screen Space position to World position

All credit goes to tosiabunio over on this forum post for this great solution.

Using Unity’s Canvas UI is excellent when you want your UI elements to scale and position correctly across different devices and aspect ratios. Learning to work with the Canvas UI properly is a bit of a nightmare but that’s a different story.

My issue was that while I do want UI elements to reposition across different aspect ratios I also want some GameObjects to have animations that seemingly interact with the UI elements. For instance, I wanted the Deck and Discard piles (UI Elements in Screen Space) to have Cards (Game Objects in World Space) come in/out of them.

GameObject Cards in World Space coming out of UI element Images in Screen Space. Works even as the UI elements move due to aspect ratio changes.

The problem is that you cannot simply have your World Space objects get the transform position of the Screen Space UI objects, the positions will not translate properly and you’ll end up with your World Space objects flying off the screen. This is where Tosiabunio’s solution comes into play when you want to ” Translate anchored overlay UI element to world position. “

var screenToWorldPosition = Camera.main.ScreenToWorldPoint(rectTransform.transform.position);

Basically, all you have to do is use the ScreenToWorldPoint method and pass it the desired UI object’s transform.position. It’s a simple one liner but this solution had evaded me for months where I was doing all kinds of crazy hacks trying to get these two positioning systems to play nice together.

Tosiabunio’s post also mentions a way to convert in the opposite direction, World Space into Screen Space:

Translate game object position from the world to overlay position in order to place UI element near that object.

To which he suggests:

RectTransformUtility.WorldToScreenPoint(Camera.main, obj.transform.position)

I haven’t tried this yet but it might be handy for others. Also, user karma0413 points out that WorldToScreenPoint can be slightly off in some situations and offers a solution which involves performing position calculations off the scale factor. Again, I haven’t tried it yet as the original one liner works perfectly for my purposes.

Let me know if this helps you and if you have any other Unity Canvas issues that you need help resolving. I’ve been working with it a lot lately and perhaps I can help or write more about common issues people face.

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