Unity ugui点击判定

前言

最近研究了下，如何判断一个ui是否可见，最后发现它跟判断一个ui是否可点击有异曲同工之妙，所以这里也记录一下。

跳转链接：Unity怎么判断图形（Graphic）是否被遮挡

---

重要函数

• GraphicRaycaster.Raycast
• Graphic.Raycaster
• ICanvasRaycastFilter.IsRaycastLocationValid

该文不对点击事件是如何发生的做讨论，读者仅需要知道，当点击事件产生时，EventSystem会遍历所有的注册的BaseRaycaster,调用接口Raycaster。

eventData是由事件系统生成的，包含当前一系列的点击数据，例如屏幕坐标，点击次数等等。
resultAppendList将用于参与点击交互UI的填充，用BaseRaycaster负责填充。

EventSystem.RaycasterAll

        /// <summary>
        /// Raycast into the scene using all configured BaseRaycasters.
        /// </summary>
        /// <param name="eventData">Current pointer data.</param>
        /// <param name="raycastResults">List of 'hits' to populate.</param>
        public void RaycastAll(PointerEventData eventData, List<RaycastResult> raycastResults)
        {
            raycastResults.Clear();
            var modules = RaycasterManager.GetRaycasters();
            var modulesCount = modules.Count;
            for (int i = 0; i < modulesCount; ++i)
            {
                var module = modules[i];
                if (module == null || !module.IsActive())
                    continue;

                module.Raycast(eventData, raycastResults);
            }

            raycastResults.Sort(s_RaycastComparer);
        }

GraphicRaycaster.Raycast

1. 调用GraphicRegistry.GetRaycastableGraphicsForCanvas(canvas)接口，拿取当前Canvas中所有打开了Raycaster交互的Graphic。（另外提一句，GraphicRegistry.GetGraphicsForCanvas(canvas)可以获得Canvas中所有Graphic）。
2. 如果Canvas不在摄像机视野内，则剔除掉。
3. 遍历Graphic，剔除掉canvasRenerer不渲染的或者绝对深度排序错误的；剔除掉“屏幕点击坐标”不在AABB包围盒中的；调用Graphic.Raycast，剔除掉自定义交互遮挡未通过的

点击查看代码

        /// <summary>
        /// Perform the raycast against the list of graphics associated with the Canvas.
        /// </summary>
        /// <param name="eventData">Current event data</param>
        /// <param name="resultAppendList">List of hit objects to append new results to.</param>
        public override void Raycast(PointerEventData eventData, List<RaycastResult> resultAppendList)
        {
            if (canvas == null)
                return;

            var canvasGraphics = GraphicRegistry.GetGraphicsForCanvas(canvas);
            if (canvasGraphics == null || canvasGraphics.Count == 0)
                return;

            int displayIndex;
            var currentEventCamera = eventCamera; // Property can call Camera.main, so cache the reference

            if (canvas.renderMode == RenderMode.ScreenSpaceOverlay || currentEventCamera == null)
                displayIndex = canvas.targetDisplay;
            else
                displayIndex = currentEventCamera.targetDisplay;

            var eventPosition = Display.RelativeMouseAt(eventData.position);
            if (eventPosition != Vector3.zero)
            {
                // We support multiple display and display identification based on event position.

                int eventDisplayIndex = (int)eventPosition.z;

                // Discard events that are not part of this display so the user does not interact with multiple displays at once.
                if (eventDisplayIndex != displayIndex)
                    return;
            }
            else
            {
                // The multiple display system is not supported on all platforms, when it is not supported the returned position
                // will be all zeros so when the returned index is 0 we will default to the event data to be safe.
                eventPosition = eventData.position;

                // We dont really know in which display the event occured. We will process the event assuming it occured in our display.
            }

            // Convert to view space
            Vector2 pos;
            if (currentEventCamera == null)
            {
                // Multiple display support only when not the main display. For display 0 the reported
                // resolution is always the desktops resolution since its part of the display API,
                // so we use the standard none multiple display method. (case 741751)
                float w = Screen.width;
                float h = Screen.height;
                if (displayIndex > 0 && displayIndex < Display.displays.Length)
                {
                    w = Display.displays[displayIndex].systemWidth;
                    h = Display.displays[displayIndex].systemHeight;
                }
                pos = new Vector2(eventPosition.x / w, eventPosition.y / h);
            }
            else
                pos = currentEventCamera.ScreenToViewportPoint(eventPosition);

            // If it's outside the camera's viewport, do nothing
            if (pos.x < 0f || pos.x > 1f || pos.y < 0f || pos.y > 1f)
                return;

            float hitDistance = float.MaxValue;

            Ray ray = new Ray();

            if (currentEventCamera != null)
                ray = currentEventCamera.ScreenPointToRay(eventPosition);

            if (canvas.renderMode != RenderMode.ScreenSpaceOverlay && blockingObjects != BlockingObjects.None)
            {
                float distanceToClipPlane = 100.0f;

                if (currentEventCamera != null)
                {
                    float projectionDirection = ray.direction.z;
                    distanceToClipPlane = Mathf.Approximately(0.0f, projectionDirection)
                        ? Mathf.Infinity
                        : Mathf.Abs((currentEventCamera.farClipPlane - currentEventCamera.nearClipPlane) / projectionDirection);
                }

                if (blockingObjects == BlockingObjects.ThreeD || blockingObjects == BlockingObjects.All)
                {
                    if (ReflectionMethodsCache.Singleton.raycast3D != null)
                    {
                        var hits = ReflectionMethodsCache.Singleton.raycast3DAll(ray, distanceToClipPlane, (int)m_BlockingMask);
                        if (hits.Length > 0)
                            hitDistance = hits[0].distance;
                    }
                }

                if (blockingObjects == BlockingObjects.TwoD || blockingObjects == BlockingObjects.All)
                {
                    if (ReflectionMethodsCache.Singleton.raycast2D != null)
                    {
                        var hits = ReflectionMethodsCache.Singleton.getRayIntersectionAll(ray, distanceToClipPlane, (int)m_BlockingMask);
                        if (hits.Length > 0)
                            hitDistance = hits[0].distance;
                    }
                }
            }

            m_RaycastResults.Clear();

            Raycast(canvas, currentEventCamera, eventPosition, canvasGraphics, m_RaycastResults);

            int totalCount = m_RaycastResults.Count;
            for (var index = 0; index < totalCount; index++)
            {
                var go = m_RaycastResults[index].gameObject;
                bool appendGraphic = true;

                if (ignoreReversedGraphics)
                {
                    if (currentEventCamera == null)
                    {
                        // If we dont have a camera we know that we should always be facing forward
                        var dir = go.transform.rotation * Vector3.forward;
                        appendGraphic = Vector3.Dot(Vector3.forward, dir) > 0;
                    }
                    else
                    {
                        // If we have a camera compare the direction against the cameras forward.
                        var cameraFoward = currentEventCamera.transform.rotation * Vector3.forward;
                        var dir = go.transform.rotation * Vector3.forward;
                        appendGraphic = Vector3.Dot(cameraFoward, dir) > 0;
                    }
                }

                if (appendGraphic)
                {
                    float distance = 0;
                    Transform trans = go.transform;
                    Vector3 transForward = trans.forward;

                    if (currentEventCamera == null || canvas.renderMode == RenderMode.ScreenSpaceOverlay)
                        distance = 0;
                    else
                    {
                        // http://geomalgorithms.com/a06-_intersect-2.html
                        distance = (Vector3.Dot(transForward, trans.position - ray.origin) / Vector3.Dot(transForward, ray.direction));

                        // Check to see if the go is behind the camera.
                        if (distance < 0)
                            continue;
                    }

                    if (distance >= hitDistance)
                        continue;

                    var castResult = new RaycastResult
                    {
                        gameObject = go,
                        module = this,
                        distance = distance,
                        screenPosition = eventPosition,
                        index = resultAppendList.Count,
                        depth = m_RaycastResults[index].depth,
                        sortingLayer = canvas.sortingLayerID,
                        sortingOrder = canvas.sortingOrder,
                        worldPosition = ray.origin + ray.direction * distance,
                        worldNormal = -transForward
                    };
                    resultAppendList.Add(castResult);
                }
            }
        }

        /// <summary>
        /// Perform a raycast into the screen and collect all graphics underneath it.
        /// </summary>
        [NonSerialized] static readonly List<Graphic> s_SortedGraphics = new List<Graphic>();
        private static void Raycast(Canvas canvas, Camera eventCamera, Vector2 pointerPosition, IList<Graphic> foundGraphics, List<Graphic> results)
        {
            // Necessary for the event system
            int totalCount = foundGraphics.Count;
            for (int i = 0; i < totalCount; ++i)
            {
                Graphic graphic = foundGraphics[i];

                // -1 means it hasn't been processed by the canvas, which means it isn't actually drawn
                if (graphic.depth == -1 || !graphic.raycastTarget || graphic.canvasRenderer.cull)
                    continue;

                if (!RectTransformUtility.RectangleContainsScreenPoint(graphic.rectTransform, pointerPosition, eventCamera))
                    continue;

                if (eventCamera != null && eventCamera.WorldToScreenPoint(graphic.rectTransform.position).z > eventCamera.farClipPlane)
                    continue;

                if (graphic.Raycast(pointerPosition, eventCamera))
                {
                    s_SortedGraphics.Add(graphic);
                }
            }

            s_SortedGraphics.Sort((g1, g2) => g2.depth.CompareTo(g1.depth));
            totalCount = s_SortedGraphics.Count;
            for (int i = 0; i < totalCount; ++i)
                results.Add(s_SortedGraphics[i]);

            s_SortedGraphics.Clear();
        }

Graphic.Raycaster

用于自定义判断点击遮挡，不用考虑射线是否在Rect范围内，不在的情况已经被过滤。

1. 拿取当前节点所有的Component组件，进行遍历。
2. 如果是Canvas，且Canvas开启了overrideSorting则不会继续向节点上层遍历。
3. 如果是CanvasGroup，判断是否开启ignoreParentGroups，开启后不再判断上层节点的CanvasGroup。
4. 判断Component组件是否有实现ICanvasRaycastFilter接口，这是一个自定义遮挡交互的接口，如果ICanvasRaycastFilter.IsRaycastLocationValid通过则代表可交互。
5. 会一直向上层遍历，但凡是有判断无法交互的情况，则直接认为该Graphic无法交互

点击查看代码

        /// <summary>
        /// When a GraphicRaycaster is raycasting into the scene it does two things. First it filters the elements using their RectTransform rect. Then it uses this Raycast function to determine the elements hit by the raycast.
        /// </summary>
        /// <param name="sp">Screen point being tested</param>
        /// <param name="eventCamera">Camera that is being used for the testing.</param>
        /// <returns>True if the provided point is a valid location for GraphicRaycaster raycasts.</returns>
        public virtual bool Raycast(Vector2 sp, Camera eventCamera)
        {
            if (!isActiveAndEnabled)
                return false;

            var t = transform;
            var components = ListPool<Component>.Get();

            bool ignoreParentGroups = false;
            bool continueTraversal = true;

            while (t != null)
            {
                t.GetComponents(components);
                for (var i = 0; i < components.Count; i++)
                {
                    var canvas = components[i] as Canvas;
                    if (canvas != null && canvas.overrideSorting)
                        continueTraversal = false;

                    var filter = components[i] as ICanvasRaycastFilter;

                    if (filter == null)
                        continue;

                    var raycastValid = true;

                    var group = components[i] as CanvasGroup;
                    if (group != null)
                    {
                        if (ignoreParentGroups == false && group.ignoreParentGroups)
                        {
                            ignoreParentGroups = true;
                            raycastValid = filter.IsRaycastLocationValid(sp, eventCamera);
                        }
                        else if (!ignoreParentGroups)
                            raycastValid = filter.IsRaycastLocationValid(sp, eventCamera);
                    }
                    else
                    {
                        raycastValid = filter.IsRaycastLocationValid(sp, eventCamera);
                    }

                    if (!raycastValid)
                    {
                        ListPool<Component>.Release(components);
                        return false;
                    }
                }
                t = continueTraversal ? t.parent : null;
            }
            ListPool<Component>.Release(components);
            return true;
        }

ICanvasRaycastFilter.IsRaycastLocationValid

这个接口比较重要，接下分析一下Image，Mask，RectMask2D，CanvasGroup分别是怎么实现该接口的

Image.IsRaycastLocationValid

1. 采样透明度：鼠标屏幕坐标采样得到像素值的alpha值
2. 阙值：Image.alphaHitTestMinimumThreshold
3. alphaHitTestMinimumThreshold 默认为 0；图像矩形内的所有射线投射事件都被视为命中。要使大于 0 的值起作用，图像使用的精灵必须具有可读取的像素。可以通过在精灵的高级纹理导入设置中启用“读/写使能”，并禁用精灵的图集化来实现这一点。
4. 当"采样透明度"值小于"阈值"时，射线投射事件将穿过图像。值为"1"会导致只有完全不透明的像素可以在图像上注册射线投射事件。测试的 alpha 值仅从图像精灵中检索，而忽略了图像的alpha（UI.Graphic.color）。

点击查看代码

        /// <summary>
        /// Calculate if the ray location for this image is a valid hit location. Takes into account a Alpha test threshold.
        /// </summary>
        /// <param name="screenPoint">The screen point to check against</param>
        /// <param name="eventCamera">The camera in which to use to calculate the coordinating position</param>
        /// <returns>If the location is a valid hit or not.</returns>
        /// <remarks> Also see See:ICanvasRaycastFilter.</remarks>
        public virtual bool IsRaycastLocationValid(Vector2 screenPoint, Camera eventCamera)
        {
            if (alphaHitTestMinimumThreshold <= 0)
                return true;

            if (alphaHitTestMinimumThreshold > 1)
                return false;

            if (activeSprite == null)
                return true;

            Vector2 local;
            if (!RectTransformUtility.ScreenPointToLocalPointInRectangle(rectTransform, screenPoint, eventCamera, out local))
                return false;

            Rect rect = GetPixelAdjustedRect();

            // Convert to have lower left corner as reference point.
            local.x += rectTransform.pivot.x * rect.width;
            local.y += rectTransform.pivot.y * rect.height;

            local = MapCoordinate(local, rect);

            // Convert local coordinates to texture space.
            Rect spriteRect = activeSprite.textureRect;
            float x = (spriteRect.x + local.x) / activeSprite.texture.width;
            float y = (spriteRect.y + local.y) / activeSprite.texture.height;

            try
            {
                return activeSprite.texture.GetPixelBilinear(x, y).a >= alphaHitTestMinimumThreshold;
            }
            catch (UnityException e)
            {
                Debug.LogError("Using alphaHitTestMinimumThreshold greater than 0 on Image whose sprite texture cannot be read. " + e.Message + " Also make sure to disable sprite packing for this sprite.", this);
                return true;
            }
        }

Mask.IsRaycastLocationValid和RectMask2D.IsRaycastLocationValid

Mask是利用模板测试来剔除，RectMask2D则计算出范围来剔除。（这里另开篇文章记录）这个范围Unity没有提供一个可用接口供用户获取，而是提供了一个通用接口，判断鼠标屏幕坐标下，RectTransform中某点是否可见。

点击查看代码 Mask

        public virtual bool IsRaycastLocationValid(Vector2 sp, Camera eventCamera)
        {
            if (!isActiveAndEnabled)
                return true;

            return RectTransformUtility.RectangleContainsScreenPoint(rectTransform, sp, eventCamera);
        }

点击查看代码 RectMask2D

        public virtual bool IsRaycastLocationValid(Vector2 sp, Camera eventCamera)
        {
            if (!isActiveAndEnabled)
                return true;

            return RectTransformUtility.RectangleContainsScreenPoint(rectTransform, sp, eventCamera, m_Padding);
        }

CanvasGroup.IsRaycastLocationValid

是否开启blocksRaycasters

点击查看代码

    /// <summary>
    ///   <para>Returns true if the Group allows raycasts.</para>
    /// </summary>
    /// <param name="sp"></param>
    /// <param name="eventCamera"></param>
    public bool IsRaycastLocationValid(Vector2 sp, Camera eventCamera) => this.blocksRaycasts;