Draw bounding rectangle (screen space) around a game object with a renderer (world space)

Unity Engine
1

Hi!

I have a game object that lives in world space in my scene. I would like to get the coordinates of the corners of the bounding rectangle for this game object’s renderer in screen space because I have UI elements that want to be positioned around this box.

Context: I’m making a tutorial and I am using panels to darken everything except for a game object that will be left un-darkened. I can do this easily with buttons that already live in screen space and have rect transforms on them, but I can’t figure out how to do this around a game object in world space. We are using a camera with orthographic projection and are using Unity version 2019.2.17f1.

Here’s what I’ve tried:

public void FocusOnRenderer(Renderer renderer) {

       // left, top, right, and bottom are Panels whose pivots are set as follows:
       // top: (1, 0)
       // right: (0, 0)
       // bottom: (0, 1)
       // left: (1, 1)
       // so when their positions are set to be the corners of the target bounding box, they will fit together nicely.

       left.gameObject.SetActive(true);
       top.gameObject.SetActive(true);
       right.gameObject.SetActive(true);
       bottom.gameObject.SetActive(true);

       Vector3 center = HandleUtility.WorldToGUIPoint(renderer.bounds.center); // center of bounding box
       Vector3 halfSize = HandleUtility.WorldToGUIPoint(renderer.bounds.extents)); // half size of bounding box

       Vector3 topRight = center + halfSize;
       Vector3 topLeft = center  + new Vector3(-halfSize.x, halfSize.y, halfSize.z);
       Vector3 bottomRight = center  + new Vector3(halfSize.x, -halfSize.y, halfSize.z);
       Vector3 bottomLeft = center  + new Vector3(-halfSize.x, -halfSize.y, halfSize.z);

       left.position = topLeft;
       top.position = topRight;
       right.position = bottomRight;
       bottom.position = bottomLeft;
   }

I think this is wrong because what I’m doing with the renderer’s bounds to compute halfSize and center aren’t giving me a bounding rectangle. I was hoping there would be an easy built in way to do this but I haven’t been able to find anything so far.

Thank you for your help!

2

You mean this?
www.youtube.com/watch?v=OOkVADKo0IM

1 Like
3

Yes! Part two of that video series had the answer thank you!

4

Used info from

! thank you @SparrowsNest for the suggestion

Here’s my code that works for me:

public void FocusOnBounds(Bounds bounds) {
        left.gameObject.SetActive(true);
        top.gameObject.SetActive(true);
        right.gameObject.SetActive(true);
        bottom.gameObject.SetActive(true);

        Vector3 c = bounds.center;
        Vector3 e = bounds.extents;

        Vector3[] worldCorners = new [] {
            new Vector3( c.x + e.x, c.y + e.y, c.z + e.z ),
            new Vector3( c.x + e.x, c.y + e.y, c.z - e.z ),
            new Vector3( c.x + e.x, c.y - e.y, c.z + e.z ),
            new Vector3( c.x + e.x, c.y - e.y, c.z - e.z ),
            new Vector3( c.x - e.x, c.y + e.y, c.z + e.z ),
            new Vector3( c.x - e.x, c.y + e.y, c.z - e.z ),
            new Vector3( c.x - e.x, c.y - e.y, c.z + e.z ),
            new Vector3( c.x - e.x, c.y - e.y, c.z - e.z ),
        };

        IEnumerable<Vector3> screenCorners = worldCorners.Select(corner => Camera.main.WorldToScreenPoint(corner));
        float maxX = screenCorners.Max(corner => corner.x);
        float minX = screenCorners.Min(corner => corner.x);
        float maxY = screenCorners.Max(corner => corner.y);
        float minY = screenCorners.Min(corner => corner.y);

        Vector3 topRight = new Vector3(maxX, maxY, 0);
        Vector3 topLeft = new Vector3(minX, maxY, 0);
        Vector3 bottomRight = new Vector3(maxX, minY, 0);
        Vector3 bottomLeft = new Vector3(minX, minY, 0);

        left.position = topLeft;
        top.position = topRight;
        right.position = bottomRight;
        bottom.position = bottomLeft;
    }
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