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

        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(zhuǎn)扭曲的中心
      uniform float4 _CenterRadius;
      //將旋轉(zhuǎn)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(biāo)變換到center坐標(biāo)系中
        o.uv = v.uv - _CenterRadius.xy;
        return o;
      }

      fixed4 frag (v2f i) : SV_Target
      {

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

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

        //根據(jù)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(biāo)返回原坐標(biāo)系中
        offest += _CenterRadius.xy; 

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

        return col;
      }
      ENDCG
    }
  }
}

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

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

//根據(jù)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(biāo)返回原坐標(biāo)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);

  }

}