Unity Texture2D.ReadPixels reads differently on Android - unity3d

Question

We're trying to capture an area of the screen for our players to share. In the editor, the capture works fine, it captures the exact area. On Android however, the area seems to vary on the device itself. On one device it captures a much larger area and on another it's a smaller area. But, the final image size is always the same. This makes me think that a scaling or translation isn't correct when capturing the screen. However, visually everything scales correctly.
I'm using Unity 2020.1.10
I assign the panel I want a screenshot of to recT.
public class ElementScreenshot : MonoBehaviour
{
public RectTransform rectT; // Assign the UI element which you wanna capture
//public Image img;
int width; // width of the object to capture
int height; // height of the object to capture
// Use this for initialization
void Start()
{
width = System.Convert.ToInt32(rectT.rect.width);
height = System.Convert.ToInt32(rectT.rect.height);
}
public IEnumerator takeScreenShot(string filePath)
{
yield return new WaitForEndOfFrame(); // it must be a coroutine
Vector2 temp = rectT.transform.position;
var startX = temp.x - width / 2;
var startY = temp.y - height / 2;
var tex = new Texture2D(width, height, TextureFormat.RGB24, false);
tex.ReadPixels(new Rect(startX, startY, width, height), 0, 0);
tex.Apply();
// Encode texture into PNG
var bytes = tex.EncodeToPNG();
Destroy(tex);
File.WriteAllBytes(filePath, bytes);
}
public string Capture()
{
var filePath = Path.Combine(Application.temporaryCachePath, "shared_image.png");
StartCoroutine(takeScreenShot(filePath)); // screenshot of a particular UI Element.
return filePath;
}
}

Answer 1

The issue was with using rect. The following change fixed the issue.
public IEnumerator takeScreenShot(string filePath)
{
yield return new WaitForEndOfFrame(); // it must be a coroutine
var r = RectTransformToScreenSpace(rectT);
var tex = new Texture2D((int)r.width, (int)r.height, TextureFormat.RGB24, false);
tex.ReadPixels(r, 0, 0);
tex.Apply();
// Encode texture into PNG
var bytes = tex.EncodeToPNG();
Destroy(tex);
File.WriteAllBytes(filePath, bytes);
}
public static Rect RectTransformToScreenSpace(RectTransform transform)
{
Vector2 size = Vector2.Scale(transform.rect.size, transform.lossyScale);
return new Rect((Vector2)transform.position - (size * 0.5f), size);
}