unity简单示例——引导聚合动画（shader+C#）

首先看一下效果

大概思路
在C#脚本每次得到目标点中心位置，目标点直径和遮罩距离目标中心点的最大距离作为当前遮罩镂空半径，然后在更新方法中利用平滑函数更新遮罩镂空半径，使其不断接近目标点直径。
在shader脚本中利用unity自带默认UIshader进行修改，在shader中利用C#传进来的中心点和直径大小计算遮罩镂空样式。（在片元着色器计算透明区域为镂空区域）

C#脚本

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.UI;
/****************************************************
作者：cg
功能：新手引导聚合动画
*****************************************************/
public class FocusAnimation : MonoBehaviour
{
    
    
    public Image Target = null;
    public Canvas Canvas = null;
    private Vector4 _center;
    private Material _material = null;
    private float _diameter;//直径
    private float _current;
    Vector3[] _cornersArray = new Vector3[4];
    private float _yVelocityTemp = 0;

    private void Awake()
    {
    
    
        Target.rectTransform.GetWorldCorners(_cornersArray);//获取目标图片在世界空间中的各个角。
        _diameter = Vector2.Distance(WoridToCanvasPos(Canvas, _cornersArray[0]), WoridToCanvasPos(Canvas, _cornersArray[2])) / 2.0f;
        float x = _cornersArray[0].x + (_cornersArray[3].x - _cornersArray[0].x) / 2.0f;
        float y = _cornersArray[0].y + (_cornersArray[1].y - _cornersArray[0].y) / 2.0f;
        Vector3 center = new Vector3(x, y, 0);
        Vector2 postion = Vector2.zero;
        RectTransformUtility.ScreenPointToLocalPointInRectangle(Canvas.transform as RectTransform, center, Canvas.GetComponent<Camera>(), out postion);

        _center = new Vector4(postion.x, postion.y, 0, 0);
        _material = GetComponent<Image>().material;
        _material.SetVector("_Center", _center);

        (Canvas.transform as RectTransform).GetWorldCorners(_cornersArray);
        for (int i = 0; i < _cornersArray.Length; i++)
        {
    
    
            _current = Mathf.Max(Vector3.Distance(WoridToCanvasPos(Canvas, _cornersArray[i]), _center), _current);
        }
        _material.SetFloat("_Silder", _current);
    }

    private void Update()
    {
    
    
        float value = Mathf.SmoothDamp(_current, _diameter, ref _yVelocityTemp, 0.3f);
        if(!Mathf.Approximately(value,_current))
        {
    
    
            _current = value;
            _material.SetFloat("_Silder", _current);
        }
    }

    private void OnGUI()
    {
    
    
        if (GUILayout.Button("Test"))
        {
    
    
            Awake();
        }
    }

    private Vector2 WoridToCanvasPos(Canvas canvas,Vector3 world)
    {
    
    
        Vector2 position = Vector2.zero;
        //将一个屏幕空间点转换为 RectTransform 的本地空间中位于其矩形平面上的一个位置
        RectTransformUtility.ScreenPointToLocalPointInRectangle(canvas.transform as RectTransform, world, canvas.GetComponent<Camera>(), out position);
        return position;
    }
}

shader脚本

Shader "cg/FocusMask"
{
	Properties
	{
		[PerRendererData] _MainTex("Sprite Texture", 2D) = "white" {}
		_Color("Tint", Color) = (1,1,1,1)

		_StencilComp("Stencil Comparison", Float) = 8
		_Stencil("Stencil ID", Float) = 0
		_StencilOp("Stencil Operation", Float) = 0
		_StencilWriteMask("Stencil Write Mask", Float) = 255
		_StencilReadMask("Stencil Read Mask", Float) = 255

		_ColorMask("Color Mask", Float) = 15


		[Toggle(UNITY_UI_ALPHACLIP)] _UseUIAlphaClip("Use Alpha Clip", Float) = 0


			//-------------------add----------------------
			  _Center("Center", vector) = (0, 0, 0, 0)
			  _Silder("_Silder", Range(0,1000)) = 1000 // sliders
			//-------------------add----------------------
	}

		SubShader
		{
			Tags
			{
				"Queue" = "Transparent"
				"IgnoreProjector" = "True"
				"RenderType" = "Transparent"
				"PreviewType" = "Plane"
				"CanUseSpriteAtlas" = "True"
			}

			Stencil
			{
				Ref[_Stencil]
				Comp[_StencilComp]
				Pass[_StencilOp]
				ReadMask[_StencilReadMask]
				WriteMask[_StencilWriteMask]
			}

			Cull Off
			Lighting Off
			ZWrite Off
			ZTest[unity_GUIZTestMode]
			Blend SrcAlpha OneMinusSrcAlpha
			ColorMask[_ColorMask]

			Pass
			{
				Name "Default"
			CGPROGRAM
				#pragma vertex vert
				#pragma fragment frag
				#pragma target 2.0

				#include "UnityCG.cginc"
				#include "UnityUI.cginc"

				#pragma multi_compile __ UNITY_UI_ALPHACLIP

				struct appdata_t
				{
					float4 vertex   : POSITION;
					float4 color    : COLOR;
					float2 texcoord : TEXCOORD0;
					UNITY_VERTEX_INPUT_INSTANCE_ID
				};

				struct v2f
				{
					float4 vertex   : SV_POSITION;
					fixed4 color : COLOR;
					float2 texcoord  : TEXCOORD0;
					float4 worldPosition : TEXCOORD1;
					UNITY_VERTEX_OUTPUT_STEREO

				};

				fixed4 _Color;
				fixed4 _TextureSampleAdd;
				float4 _ClipRect;
				//-------------------add----------------------
				float _Silder;
				float2 _Center;
				//-------------------add----------------------
				v2f vert(appdata_t IN)
				{
					v2f OUT;
					UNITY_SETUP_INSTANCE_ID(IN);
					UNITY_INITIALIZE_VERTEX_OUTPUT_STEREO(OUT);
					OUT.worldPosition = IN.vertex;
					OUT.vertex = UnityObjectToClipPos(OUT.worldPosition);

					OUT.texcoord = IN.texcoord;

					OUT.color = IN.color * _Color;
					return OUT;
				}

				sampler2D _MainTex;

				fixed4 frag(v2f IN) : SV_Target
				{
					half4 color = (tex2D(_MainTex, IN.texcoord) + _TextureSampleAdd) * IN.color;

					color.a *= UnityGet2DClipping(IN.worldPosition.xy, _ClipRect);

					#ifdef UNITY_UI_ALPHACLIP
					clip(color.a - 0.001);
					#endif
					//-------------------add----------------------
					color.a *= (distance(IN.worldPosition.xy,_Center.xy) > _Silder);
					color.rgb *= color.a;
					//-------------------add----------------------
					return color;

				}
			ENDCG
			}
		}
}