/*====================================================

    屏幕扭曲特效Shader

======================================================*/
Shader "Hidden/TwirlEffects"
{
 Properties
 {
  _MainTex ("Texture", 2D) = "white" {}

 }
 SubShader
 {
  // No culling or depth
  Cull Off ZWrite Off ZTest Always

  Pass
  {
   CGPROGRAM
   #pragma vertex vert
   #pragma fragment frag

   #include "UnityCG.cginc"

   uniform sampler2D _MainTex;
   uniform float4 _MainTex_TexelSize;
   half4 _MainTex_ST;

   //旋轉扭曲的中心
   uniform float4 _CenterRadius;
   //將旋轉矩陣傳入
   uniform float4x4 _RotationMatrix;

   struct appdata
   {
    float4 vertex : POSITION;
    float2 uv : TEXCOORD0;
   };

   struct v2f
   {
    float2 uv : TEXCOORD0;
    float4 vertex : SV_POSITION;
   };

   v2f vert (appdata v)
   {
    v2f o;
    o.vertex = mul(UNITY_MATRIX_MVP, v.vertex);
    //將uv坐標變換到center坐標系中
    o.uv = v.uv - _CenterRadius.xy;
    return o;
   }

   fixed4 frag (v2f i) : SV_Target
   {

    float2 offest = i.uv;
    //利用旋轉矩陣旋轉uv
    float2 distortedOffset = MultiplyUV(_RotationMatrix,offest.xy);

    //計算uv點在旋轉圓中的位置
    float2 tmp = offest / _CenterRadius.zw;
    float t = min(1,length(tmp));

    //根據uv點在圓中的位置插值uv移動的位置
    offest =lerp(distortedOffset,offest,t);

    //將uv坐標返回原坐標系中
    offest += _CenterRadius.xy; 

    fixed4 col = tex2D(_MainTex, UnityStereoScreenSpaceUVAdjust(offest, _MainTex_ST));

    return col;
   }
   ENDCG
  }
 }
}

 float2 offest = i.uv;
//利用旋轉矩陣旋轉uv
 float2 distortedOffset = MultiplyUV(_RotationMatrix,offest.xy);

 //計算uv點在旋轉圓中的位置
float2 tmp = offest / _CenterRadius.zw;
float t = min(1,length(tmp));

//根據uv點在圓中的位置插值uv移動的位置
offest =lerp(distortedOffset,offest,t);

//將uv坐標返回原坐標系中
offest += _CenterRadius.xy; 

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class TwirlScripts : MonoBehaviour {

 [ExecuteInEditMode]

 public Vector2 radius = new Vector2(0.3f, 0.3f);

 public Vector2 center = new Vector2(0.5f, 0.5f);

 [Range(0.0f, 360.0f)]
 public float angle = 0.0f;

 public Material material;

 private void OnRenderImage(RenderTexture source, RenderTexture destination)
 {

  Matrix4x4 rotationMatrix = Matrix4x4.TRS(Vector3.zero, Quaternion.Euler(0, 0, angle), Vector3.one);

  material.SetMatrix("_RotationMatrix", rotationMatrix);
  material.SetVector("_CenterRadius", new Vector4(center.x, center.y, radius.x, radius.y));

  Graphics.Blit(source, destination, material);

 }

}