简单的折射效果

通过 GrabPass 实现

Shader "Unlit/Glass"
{
    Properties
    {
        _BumpAmt ("Distortion", Range (0,100)) = 10
        _TintAmt ("Tint Amount", Range(0,1)) = 0.1
        _BlurAmt ("Blur Amount", Range (0,1)) = 0.1
        _MainTex ("Texture", 2D) = "white" {}
        _BumpMap ("Normal Map", 2D) = "bump" {}
    }
    SubShader
    {
        Tags { "Queue" = "Transparent" } // 重要：使用透明队列保障其他物体已绘制在屏幕上

        GrabPass { "_GrabBlurTexture" }

        Pass
        {
            CGPROGRAM
            #pragma vertex vert
            #pragma fragment frag
            #include "UnityCG.cginc"

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

            struct v2f
            {
                float4 uv : TEXCOORD0;
                float4 grabPos : TEXCOORD1;
                float4 vertex : SV_POSITION;
            };

            float _BumpAmt;
            float _TintAmt;
            float _BlurAmt;
            sampler2D _MainTex, _BumpMap;
            float4 _MainTex_ST, _BumpMap_ST;
            sampler2D _GrabBlurTexture;
            float4 _GrabBlurTexture_TexelSize; // texture size, x:1.0/width y:1.0/height z:width w:height

            v2f vert (appdata v)
            {
                v2f o;
                o.vertex = UnityObjectToClipPos(v.vertex);
                o.uv.xy = TRANSFORM_TEX(v.uv, _MainTex);
                o.uv.zw = TRANSFORM_TEX(v.uv, _BumpMap);
                o.grabPos = ComputeGrabScreenPos(o.vertex);
                return o;
            }

            fixed4 frag (v2f i) : SV_Target
            {
                // 从 normalmap 中采样出凹凸值
                float2 bump = UnpackNormal(tex2D(_BumpMap, i.uv.zw)).xy;

                // 偏移量(*_TexelSize.xy 的意义是偏移值按抓取的纹理的单位像素进行缩放)
                float2 offset = bump * _BumpAmt * _GrabBlurTexture_TexelSize.xy;

                i.grabPos.xy = offset + i.grabPos.xy;

                fixed4 col = tex2D(_GrabBlurTexture, i.grabPos.xy / i.grabPos.w); // 除以 w 后得到屏幕空间采样坐标

                // blur (这是一个比较垃圾的模糊效果)
                float blur = _BlurAmt / 100;
                col += tex2D(_GrabBlurTexture, grabuv + float2(-blur, 0));
                col += tex2D(_GrabBlurTexture, grabuv + float2(blur, 0));
                col += tex2D(_GrabBlurTexture, grabuv + float2(0, blur));
                col += tex2D(_GrabBlurTexture, grabuv + float2(0, -blur));
                col = col / 5;

                fixed4 tint = tex2D(_MainTex, i.uv.xy);
                col = lerp (col, tint, _TintAmt);
                return col;
            }
            ENDCG
        }
    }
}

通过 Command Buffers 实现

// 使用 command buffer 来生成 RT
public class ComdBuf : MonoBehaviour
{
    // 在摄像机渲染之前执行
    void OnWillRenderObject()
    {
        var cam = Camera.current;
        CommandBuffer buff = new CommandBuffer();

        // 申请 RT
        int rtID = Shader.PropertyToID("_GrabBlurTexture");
        buff.GetTemporaryRT(rtID, -1, -1, 0, FilterMode.Bilinear); // -1 for camera pixel width or height

        // blit 方法接受 RT 的标识符 RenderTargetIdentifier (即 rtID)
        buff.Blit(BuiltinRenderTextureType.CurrentActive, rtID); // 将当前渲染 RT 复制给 rtID

        // 通过该命令使在 shader 中可通过 sampler2D _GrabBlurTexture 取得该 RT
        buff.SetGlobalTexture(rtID, rtID); // 第一个参数是 shader 中的变量名，第二个是名称所标识的 RT

        // 执行时机
        cam.AddCommandBuffer(CameraEvent.AfterSkybox, buff);
    }
}

接着可使用上面的 Shader 并去掉 GrabPass { “_GrabBlurTexture” } 即可达到一样的效果