Check if UI elements/RectTransform are overlapping

Question

I\'d like to know how I check whether two UI Panels on my Unity Canvas are overlapping each other.

Currently I am doing this by comparing the canvas elements Rects

Answer 1

Convert the RectTransform to Rect then check if it overlaps.

Here is a simple function that can do that:

bool rectOverlaps(RectTransform rectTrans1, RectTransform rectTrans2)
{
    Rect rect1 = new Rect(rectTrans1.localPosition.x, rectTrans1.localPosition.y, rectTrans1.rect.width, rectTrans1.rect.height);
    Rect rect2 = new Rect(rectTrans2.localPosition.x, rectTrans2.localPosition.y, rectTrans2.rect.width, rectTrans2.rect.height);

    return rect1.Overlaps(rect2);
}

Usage:

public RectTransform uiRect1;
public RectTransform uiRect2;

void Update()
{
    if (rectOverlaps(uiRect1, uiRect2))
    {
        Debug.Log("Overlaps");
    }else
    {
        Debug.Log("Does not Overlap");
    }
}

Even better, make it an extension method:

public static class ExtensionMethod
{
    public static bool rectOverlaps(this RectTransform rectTrans1, RectTransform rectTrans2)
    {
        Rect rect1 = new Rect(rectTrans1.localPosition.x, rectTrans1.localPosition.y, rectTrans1.rect.width, rectTrans1.rect.height);
        Rect rect2 = new Rect(rectTrans2.localPosition.x, rectTrans2.localPosition.y, rectTrans2.rect.width, rectTrans2.rect.height);

        return rect1.Overlaps(rect2);
    }
}

Now, you can do

public RectTransform uiRect1;
public RectTransform uiRect2;

void Update()
{
    if (uiRect1.rectOverlaps(uiRect2))
    {

    }

    //OR

    if (uiRect2.rectOverlaps(uiRect1))
    {

    }
}

Answer 2

Updated version considering scale of the rectTransform.

public static class RectTransformExtensions
{

    public static bool Overlaps(this RectTransform a, RectTransform b) {
        return a.WorldRect().Overlaps(b.WorldRect());
    }
    public static bool Overlaps(this RectTransform a, RectTransform b, bool allowInverse) {
        return a.WorldRect().Overlaps(b.WorldRect(), allowInverse);
    }

    public static Rect WorldRect(this RectTransform rectTransform) {
        Vector2 sizeDelta = rectTransform.sizeDelta;
        float rectTransformWidth = sizeDelta.x * rectTransform.lossyScale.x;
        float rectTransformHeight = sizeDelta.y * rectTransform.lossyScale.y;

        Vector3 position = rectTransform.position;
        return new Rect(position.x - rectTransformWidth / 2f, position.y - rectTransformHeight / 2f, rectTransformWidth, rectTransformHeight);
    }
}