Graphic Raycaster

在UGUI中最主要的射线发生组件。其源码中最主要的方法就是Raycast

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namespace UnityEngine.UI
{
    [AddComponentMenu("Event/Graphic Raycaster")]
    [RequireComponent(typeof(Canvas))]
    /// <summary>
    /// A derived BaseRaycaster to raycast against Graphic elements.
    /// </summary>
    public class GraphicRaycaster : BaseRaycaster
    {
        /// <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)
        {
			//...
            var canvasGraphics = GraphicRegistry.GetRaycastableGraphicsForCanvas(canvas);//获取当前Canvas下所有Graphic子组件
            //...
            var currentEventCamera = eventCamera; // 确认事件相机，默认是主相机
            //获取当前的显示器
            if (canvas.renderMode == RenderMode.ScreenSpaceOverlay || currentEventCamera == null)
    			displayIndex = canvas.targetDisplay;
			else
    			displayIndex = currentEventCamera.targetDisplay;
            //...
            //下面是根据显示器获取分辨率的逻辑，将主显示映射到pos这个变量里（），pos是介于0~1的。如果是在副显示器操作就直接返回
            Vector2 pos；
            if (currentEventCamera == null)
			{
                //...
            }
            //...
            //根据Graphic Raycast中设置的BlockingObjects和renderMode获取hitDistance，即射线击中的距离
            if (canvas.renderMode != RenderMode.ScreenSpaceOverlay && blockingObjects != BlockingObjects.None)
            {
#if PACKAGE_PHYSICS
    //...
    			hitDistance = hits[0].distance;
#endif
#if PACKAGE_PHYSICS2D
    			hitDistance = hits[0].distance;
#endif
            }
            //...
            Raycast(canvas, currentEventCamera, eventPosition, canvasGraphics, m_RaycastResults);//这是一个静态重载，Raycast筛选的主要逻辑
            //根据上面的筛选，得到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)//筛选是否一个反面的元素，交给appendGraphic
                {
                    //...
                }
                if (appendGraphic)//如果是一个正面的元素，筛选是否在相机的背面
				{
                    //...
                    if (distance >= hitDistance)//这里通过一个公式计算出了当前元素和摄像机的距离distance，它要小于hitDistance（点击击中的最远距离）才行
    				continue;
					var castResult = new RaycastResult
					{
                        //...
                    }
                    resultAppendList.Add(castResult);//最终的结果都要加入结果的list中
                }
            }
        }
        
        //...
        /// <summary>
        /// Perform a raycast into the screen and collect all graphics underneath it.
        /// </summary>
        [NonSerialized] static readonly List<Graphic> s_SortedGraphics = new List<Graphic>();
        //这个方法主要对Graphic的状态进行筛选
        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];

                // graphic的深度是-1就表示当前UI元素根本不会绘制在屏幕上
                //如果UI元素没有打开raycastTarget，也被过滤掉
                if (!graphic.raycastTarget || graphic.canvasRenderer.cull || graphic.depth == -1)
                    continue;
				//判断当前点击事件是否在目标物体的Rect里面
                if (!RectTransformUtility.RectangleContainsScreenPoint(graphic.rectTransform, pointerPosition, eventCamera, graphic.raycastPadding))
                    continue;
				//当前点击事件的z坐标是否超出了相机的最远面
                if (eventCamera != null && eventCamera.WorldToScreenPoint(graphic.rectTransform.position).z > eventCamera.farClipPlane)
                    continue;
				//使用Grapic.Raycast判断，主要是判断当前组件是否继承ICanvasRaycastFilter接口，具体可见源码
                if (graphic.Raycast(pointerPosition, eventCamera))
                {
                    s_SortedGraphics.Add(graphic);
                }
            }

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

            s_SortedGraphics.Clear();
        }
    }