前言：我想实现一个功能，给你一张图，鼠标点击这张图后，输出Hello World!，怎么实现？
如果要我们实现，怎么实现呢？
首先我们需要在Update中每帧获取鼠标的状态，缓存起来，大概逻辑是
void Update(){
m_MouseData = UnityInternal.CaptureMouseData();
}
鼠标的状态包括，每帧，鼠标的位置，鼠标按下还是抬起，没了。
其次，我们需要在uGUI里Update中每帧判断鼠标的状态和鼠标当前碰到了哪个物体。
如果上一帧鼠标状态为抬起，并且这一帧鼠标状态为按下，那么表示鼠标点击了。
每帧从鼠标当前位置发射射线，根据对应的规则，找到碰撞的所有物体。
然后按照一定规则，把碰撞的所有物体排序，只取第一个。
最后，我们按照冒泡原则触发该物体的点击/悬浮/按下/抬起事件。
所谓冒泡原则就是，从该物体开始，查询是否有可触发事件的Handler，一直往parent查找。
我们给这张图片的点击事件添加Handler，然后添加回调，回调中输出HelloWorld。
好接下来我们看看uGUI怎么做的。
有一个继承自UIBehaviour的类BaseInput，里面定义了若干个鼠标的状态，例如mousePosition，GetMouseButton等。其内部的实现是基于Unity的Input类，没什么好说的。
值得一提的是，Unity推荐使用
Input System Package来代替Input Manager
有一个继承自UIBehaviour的抽象类BaseInputModule，有一个Process方法，uGUI正是在该方法里进行每帧判断的。
/// <summary>
/// Process the current tick for the module.
/// </summary>
public abstract void Process();
BaseInputModule有一个BaseInput字段，这个BaseInput会自动地随BaseInputModule创建。
/// <summary>
/// The current BaseInput being used by the input module.
/// </summary>
public BaseInput input
{
get
{
if (m_InputOverride != null)
return m_InputOverride;
if (m_DefaultInput == null)
{
var inputs = GetComponents<BaseInput>();
foreach (var baseInput in inputs)
{
// We dont want to use any classes that derrive from BaseInput for default.
if (baseInput != null && baseInput.GetType() == typeof(BaseInput))
{
m_DefaultInput = baseInput;
break;
}
}
if (m_DefaultInput == null)
m_DefaultInput = gameObject.AddComponent<BaseInput>();
}
return m_DefaultInput;
}
}
有哪些类继承了BaseInputModule呢？有PointerInputModule继承了；然后StandloneInputModule和TouchInputModule又都分别继承了PointerInputModule，顾名思义，后者是给屏幕触摸用的。
如果输入系统为
Input System Package，那么会有一个类InputSystemUIInputModule继承自BaseInputModule，并且该类中完全抛弃了BaseInput字段，转而用Input System Package的接口来获取鼠标状态。
在StandaloneInputModule中重写了Process方法，里面调用了ProcessMouseEvent方法，这个方法会调用一个方法：
GetMousePointerEventData，返回一个类MouseState，这个类包含了鼠标的移动和点击状态，以及从鼠标位置发射射线碰撞的第一个RaycastResult信息。很重要。
protected virtual MouseState GetMousePointerEventData(int id)
{
// Populate the left button...
PointerEventData leftData;
var created = GetPointerData(kMouseLeftId, out leftData, true);
leftData.Reset();
if (created)
leftData.position = input.mousePosition;
Vector2 pos = input.mousePosition;
if (Cursor.lockState == CursorLockMode.Locked)
{
// We don't want to do ANY cursor-based interaction when the mouse is locked
leftData.position = new Vector2(-1.0f, -1.0f);
leftData.delta = Vector2.zero;
}
else
{
leftData.delta = pos - leftData.position;
leftData.position = pos;
}
leftData.scrollDelta = input.mouseScrollDelta;
leftData.button = PointerEventData.InputButton.Left;
eventSystem.RaycastAll(leftData, m_RaycastResultCache);
var raycast = FindFirstRaycast(m_RaycastResultCache);
leftData.pointerCurrentRaycast = raycast;
m_RaycastResultCache.Clear();
// copy the apropriate data into right and middle slots
PointerEventData rightData;
GetPointerData(kMouseRightId, out rightData, true);
CopyFromTo(leftData, rightData);
rightData.button = PointerEventData.InputButton.Right;
PointerEventData middleData;
GetPointerData(kMouseMiddleId, out middleData, true);
CopyFromTo(leftData, middleData);
middleData.button = PointerEventData.InputButton.Middle;
m_MouseState.SetButtonState(PointerEventData.InputButton.Left, StateForMouseButton(0), leftData);
m_MouseState.SetButtonState(PointerEventData.InputButton.Right, StateForMouseButton(1), rightData);
m_MouseState.SetButtonState(PointerEventData.InputButton.Middle, StateForMouseButton(2), middleData);
return m_MouseState;
}
通过input填充鼠标状态，传给Raycast进行射线检测；将排序后的结果只取第一个。把数据复制为三分：左键、右键和中键。
然后设置鼠标点击状态
/// <summary>
/// Given a mouse button return the current state for the frame.
/// </summary>
/// <param name="buttonId">Mouse button ID</param>
protected PointerEventData.FramePressState StateForMouseButton(int buttonId)
{
var pressed = input.GetMouseButtonDown(buttonId);
var released = input.GetMouseButtonUp(buttonId);
if (pressed && released)
return PointerEventData.FramePressState.PressedAndReleased;
if (pressed)
return PointerEventData.FramePressState.Pressed;
if (released)
return PointerEventData.FramePressState.Released;
return PointerEventData.FramePressState.NotChanged;
}
public void RaycastAll(PointerEventData eventData, List<RaycastResult> raycastResults)
{
raycastResults.Clear();
var modules = RaycasterManager.GetRaycasters();
for (int i = 0; i < modules.Count; ++i)
{
var module = modules[i];
if (module == null || !module.IsActive())
continue;
module.Raycast(eventData, raycastResults);
}
raycastResults.Sort(s_RaycastComparer);
}
没什么好说的
有一个继承自UIBehaviour的抽象类BaseRaycaster，提供了也给抽象方法。
public abstract void Raycast(PointerEventData eventData, List<RaycastResult> resultAppendList);
其中PointerEventData就是上文提到的鼠标的状态，给定鼠标的状态信息，进行射线检测，把检测到的所有Result都添加到列表中。
具体实现包括Physics(2D)Raycaster和GraphicRaycaster，这里我们注重分析GraphicRaycaster。
/// <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; // Propery 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;
if (currentEventCamera == null || canvas.renderMode == RenderMode.ScreenSpaceOverlay)
distance = 0;
else
{
Transform trans = go.transform;
Vector3 transForward = trans.forward;
// 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
};
resultAppendList.Add(castResult);
}
}
}
前置一些条件判断，
1.如果该Canvas下没有可供检测的Graphic，那么不执行；
2.如果当前鼠标点击所在的屏幕和当前Canvas所在的屏幕不一致，那么不执行；
3.如果超出了摄像机的viewport，那么不执行；
4.如果有遮挡需求，那么找到命中的第一个物体的距离；
5.进行射线检测
6.如果忽略反向Graphic，那么会剔除反向的Graphic
7.剔除距离<0或者>hitDistance的结果
8.将结果保存
private static void Raycast(Canvas canvas, Camera eventCamera, Vector2 pointerPosition, IList<Graphic> foundGraphics, List<Graphic> results)
{
// Debug.Log("ttt" + pointerPoision + ":::" + camera);
// 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));
// StringBuilder cast = new StringBuilder();
totalCount = s_SortedGraphics.Count;
for (int i = 0; i < totalCount; ++i)
results.Add(s_SortedGraphics[i]);
// Debug.Log (cast.ToString());
s_SortedGraphics.Clear();
}
遍历所有的Graphic
1.如果depth为-1，或者raycastTarget为false，或者其下的canvasRenderer被cull了，那么不执行；
2.如果点击的位置在RectTransform外面，那么不执行；
3.如果graphic的z位置超出了摄像机的farClipPlane，那么不执行（仅针对于eventCamera不为null的情况）；
4.执行Graphic的Raycast方法；
5.根据depth排序；
Graphic的Raycast方法：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;
}
其实Graphic的Raycast主要是为了判断是否有组件导致不可点击。注意到中间有ICanvasRaycastFilter.IsRaycastLocationValid，这个主要是给遮罩和透明材质用的。
其中Mask和RectMask2D的实现都为
public virtual bool IsRaycastLocationValid(Vector2 sp, Camera eventCamera)
{
if (!isActiveAndEnabled)
return true;
return RectTransformUtility.RectangleContainsScreenPoint(rectTransform, sp, eventCamera);
}
其中Image的实现为
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);
// Normalize local coordinates.
Rect spriteRect = activeSprite.textureRect;
Vector2 normalized = new Vector2(local.x / spriteRect.width, local.y / spriteRect.height);
// Convert to texture space.
float x = Mathf.Lerp(spriteRect.x, spriteRect.xMax, normalized.x) / activeSprite.texture.width;
float y = Mathf.Lerp(spriteRect.y, spriteRect.yMax, normalized.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;
}
}
主要是判断图片某个像素点的透明度a和alphaHitTestMinimumThreshold的大小。
RaycastResult排序private static int RaycastComparer(RaycastResult lhs, RaycastResult rhs)
{
if (lhs.module != rhs.module)
{
var lhsEventCamera = lhs.module.eventCamera;
var rhsEventCamera = rhs.module.eventCamera;
if (lhsEventCamera != null && rhsEventCamera != null && lhsEventCamera.depth != rhsEventCamera.depth)
{
// need to reverse the standard compareTo
if (lhsEventCamera.depth < rhsEventCamera.depth)
return 1;
if (lhsEventCamera.depth == rhsEventCamera.depth)
return 0;
return -1;
}
if (lhs.module.sortOrderPriority != rhs.module.sortOrderPriority)
return rhs.module.sortOrderPriority.CompareTo(lhs.module.sortOrderPriority);
if (lhs.module.renderOrderPriority != rhs.module.renderOrderPriority)
return rhs.module.renderOrderPriority.CompareTo(lhs.module.renderOrderPriority);
}
if (lhs.sortingLayer != rhs.sortingLayer)
{
// Uses the layer value to properly compare the relative order of the layers.
var rid = SortingLayer.GetLayerValueFromID(rhs.sortingLayer);
var lid = SortingLayer.GetLayerValueFromID(lhs.sortingLayer);
return rid.CompareTo(lid);
}
if (lhs.sortingOrder != rhs.sortingOrder)
return rhs.sortingOrder.CompareTo(lhs.sortingOrder);
if (lhs.depth != rhs.depth)
return rhs.depth.CompareTo(lhs.depth);
if (lhs.distance != rhs.distance)
return lhs.distance.CompareTo(rhs.distance);
return lhs.index.CompareTo(rhs.index);
}
没什么好说的，通过各种排序来找到第一个射线碰撞的结果。
在StandaloneInputModule中有一个ProcessMouseEvent方法，用来每帧处理鼠标事件
protected void ProcessMouseEvent(int id)
{
var mouseData = GetMousePointerEventData(id);
var leftButtonData = mouseData.GetButtonState(PointerEventData.InputButton.Left).eventData;
m_CurrentFocusedGameObject = leftButtonData.buttonData.pointerCurrentRaycast.gameObject;
// Process the first mouse button fully
ProcessMousePress(leftButtonData);
ProcessMove(leftButtonData.buttonData);
ProcessDrag(leftButtonData.buttonData);
// Now process right / middle clicks
ProcessMousePress(mouseData.GetButtonState(PointerEventData.InputButton.Right).eventData);
ProcessDrag(mouseData.GetButtonState(PointerEventData.InputButton.Right).eventData.buttonData);
ProcessMousePress(mouseData.GetButtonState(PointerEventData.InputButton.Middle).eventData);
ProcessDrag(mouseData.GetButtonState(PointerEventData.InputButton.Middle).eventData.buttonData);
if (!Mathf.Approximately(leftButtonData.buttonData.scrollDelta.sqrMagnitude, 0.0f))
{
var scrollHandler = ExecuteEvents.GetEventHandler<IScrollHandler>(leftButtonData.buttonData.pointerCurrentRaycast.gameObject);
ExecuteEvents.ExecuteHierarchy(scrollHandler, leftButtonData.buttonData, ExecuteEvents.scrollHandler);
}
}
首先是通过GetMousePointerEventData获取必要数据，然后分别处理诸如鼠标点击、移动和拖拽。