Got it, let's break down how to handle both of these UI occlusion checks in Unity—since you mentioned GameObjects, I'm assuming we're working in that engine. Here's how to tackle each scenario:

1. Checking if One UI Element Occludes Another UI Element #

When you trigger a popup panel (like your screenshot 2) from a target UI element (screenshot 1's circled item), you need to validate two critical things: whether their areas overlap, and if the popup is actually rendered on top of the target.

Step-by-Step Implementation: #

• First, grab the RectTransform components of both elements (let's call them targetRect and popupRect).
• Check if their screen-space rectangles overlap using Unity's utility methods:

  // Convert UI rects to screen-space coordinates, accounting for canvas scaling
  Canvas targetCanvas = targetRect.GetComponentInParent<Canvas>();
  Canvas popupCanvas = popupRect.GetComponentInParent<Canvas>();
  
  Rect targetScreenRect = RectTransformUtility.PixelAdjustRect(targetRect, targetCanvas);
  Rect popupScreenRect = RectTransformUtility.PixelAdjustRect(popupRect, popupCanvas);
  
  // Check for overlap
  bool rectsOverlap = targetScreenRect.Overlaps(popupScreenRect);
  

• Next, confirm the popup is rendered on top. UI rendering order depends on three factors—here's how to check them programmatically:

  bool isPopupOnTop = false;
  
  // Case 1: Both elements are on the same canvas
  if (targetCanvas == popupCanvas)
  {
      // Higher sibling index = renders later (on top)
      isPopupOnTop = popupRect.GetSiblingIndex() > targetRect.GetSiblingIndex();
  }
  // Case 2: Different canvases
  else
  {
      // First compare sorting layers
      if (popupCanvas.sortingLayerID != targetCanvas.sortingLayerID)
      {
          int popupLayerPriority = SortingLayer.GetLayerValueFromID(popupCanvas.sortingLayerID);
          int targetLayerPriority = SortingLayer.GetLayerValueFromID(targetCanvas.sortingLayerID);
          isPopupOnTop = popupLayerPriority > targetLayerPriority;
      }
      // Same sorting layer? Compare canvas sorting order
      else
      {
          isPopupOnTop = popupCanvas.sortingOrder > targetCanvas.sortingOrder;
      }
  }
  
  // Final check: overlap exists AND popup is on top
  bool isPopupOccludingTarget = rectsOverlap && isPopupOnTop;
  

2. Checking if a UI Element Is Rendered on Top of a 3D GameObject #

For this scenario (screenshot 3), you need to verify two things: the UI covers the GameObject's screen position, and the UI is the topmost element at that point (so it's not hidden behind the 3D object).

Step-by-Step Implementation: #

• Start by getting your main camera (or the camera rendering the GameObject/UI) and the UI element's RectTransform.
• Convert the GameObject's world position to screen-space coordinates:

  Camera mainCamera = Camera.main; // Use your target camera if not main
  Vector3 gameObjectWorldPos = yourGameObject.transform.position;
  Vector2 gameObjectScreenPos = mainCamera.WorldToScreenPoint(gameObjectWorldPos);
  

• Check if this screen position falls inside the UI element's bounds:

  Canvas uiCanvas = yourUIElement.GetComponentInParent<Canvas>();
  bool isPosInsideUI = RectTransformUtility.RectangleContainsScreenPoint(yourUIElementRect, gameObjectScreenPos, uiCanvas.worldCamera);
  

• Finally, confirm the UI is the topmost element at that screen position using Unity's EventSystem raycast:

  bool isUIOnTopOfGameObject = false;
  
  PointerEventData pointerData = new PointerEventData(EventSystem.current);
  pointerData.position = gameObjectScreenPos;
  List<RaycastResult> raycastResults = new List<RaycastResult>();
  
  // Get all UI elements under the point
  EventSystem.current.RaycastAll(pointerData, raycastResults);
  
  // Check if our UI is the first (topmost) result
  isUIOnTopOfGameObject = raycastResults.Count > 0 && raycastResults[0].gameObject == yourUIElement.gameObject;
  

• Combine the checks to get the final result:

  bool isUIOverGameObject = isPosInsideUI && isUIOnTopOfGameObject;
  

内容的提问来源于stack exchange，提问作者Ido Ben Shalom