Bounding box onscreen correct, but shifted up when I use the same rect to get a Texture2d

Question

So I have a small script that takes screenshots of a cube with a 2d boundingbox drawn around it and then of the same cube, but just the contents of the bounding box.

I do this first by a standard call to Screen

ScreenCapture.CaptureScreenshot(filename)

then I call SnapShotInBoundingBox() in my code to create a Texture2d from the rect of the bounding box and save that as a screenshot.

The problem I have is the texture when saved seems to shift the image up a few pixels.

public void OnGUI()  //draws the boundingbox 
{

   Bounds b = theCube.GetComponent<Renderer>().bounds;
   Camera cam = Camera.main;
    if (cam == null) return;
   //The object is behind us
   if (cam.WorldToScreenPoint(b.center).z < 0) return;

   //All 8 vertices of the bounds
   pts[0] = cam.WorldToScreenPoint(new Vector3(b.center.x + b.extents.x, b.center.y + b.extents.y, b.center.z + b.extents.z));
   pts[1] = cam.WorldToScreenPoint(new Vector3(b.center.x + b.extents.x, b.center.y + b.extents.y, b.center.z - b.extents.z));
   pts[2] = cam.WorldToScreenPoint(new Vector3(b.center.x + b.extents.x, b.center.y - b.extents.y, b.center.z + b.extents.z));
   pts[3] = cam.WorldToScreenPoint(new Vector3(b.center.x + b.extents.x, b.center.y - b.extents.y, b.center.z - b.extents.z));
   pts[4] = cam.WorldToScreenPoint(new Vector3(b.center.x - b.extents.x, b.center.y + b.extents.y, b.center.z + b.extents.z));
   pts[5] = cam.WorldToScreenPoint(new Vector3(b.center.x - b.extents.x, b.center.y + b.extents.y, b.center.z - b.extents.z));
   pts[6] = cam.WorldToScreenPoint(new Vector3(b.center.x - b.extents.x, b.center.y - b.extents.y, b.center.z + b.extents.z));
   pts[7] = cam.WorldToScreenPoint(new Vector3(b.center.x - b.extents.x, b.center.y - b.extents.y, b.center.z - b.extents.z));

   //Get them in GUI space
   for (int i = 0; i < pts.Length; i++) pts[i].y = Screen.height - pts[i].y;

   //Calculate the min and max positions
   Vector3 min = pts[0];
   Vector3 max = pts[0];
   for (int i = 1; i < pts.Length; i++)
   {
       min = Vector3.Min(min, pts[i]);
       max = Vector3.Max(max, pts[i]);
   }

   //Construct a rect of the min and max positions and apply some margin
   r = Rect.MinMaxRect(min.x, min.y, max.x, max.y);
   r.xMin -= BoundingBoxMargin;
   r.xMax += BoundingBoxMargin;
   r.yMin -= BoundingBoxMargin;
   r.yMax += BoundingBoxMargin;

    //Render the bounding box
    GUI.backgroundColor = new Color(0, 0, 0, 0);

    GUI.DrawTexture(r, boundingBoxTexture);
}

byte[] SnapShotInBoundingBox()
{

    Rect lasso = new Rect(r.x, r.y, r.width+3, r.height);
    Debug.Log(lasso);
    tex = new Texture2D((int)lasso.width, (int)lasso.height, TextureFormat.RGBA32,false);
    tex.ReadPixels(lasso, 0, 0);        //only render what's inside the bounding box,including the box itself
    tex.Apply();

    return tex.EncodeToJPG();

}

derHugo derHugo · Accepted Answer · 2019-01-17T17:00:44

I think the reason why the two snapshots result in different images is that

The CaptureScreenshot returns immediately on Android. The screen capture continues in the background. The resulting screen shot is saved in the file system after a few seconds.

Meanwhile the camera might move so that SnapShotInBoundingBox(); returns a slightly different picture.

You should probably call the methods in the opposite order:

SnapShotInBoundingBox();
ScreenCapture.CaptureScreenshot(filename);

Bounding box onscreen correct, but shifted up when I use the same rect to get a Texture2d

1 Answers