用法

将下面的Shader对应的材质设置到UI中背景图的Material上，可看到该背景图背后的所有物件都被模糊了。

调整“Size”可控制模糊程度。

示意

模糊遮罩.gif

Shader

SimpleBlur.shader

Shader "Custom/SimpleBlur" {
    Properties {
        _Color ("Main Color", Color) = (1,1,1,1)
        _BumpAmt  ("Distortion", Range (0,255)) = 10
        _MainTex ("Tint Color (RGB)", 2D) = "white" {}
        _BumpMap ("Normalmap", 2D) = "bump" {}
        _Size ("Size", Range(0, 100)) = 1
    }
   
    Category {
   
        // We must be transparent, so other objects are drawn before this one.
        Tags { "Queue"="Transparent" "IgnoreProjector"="True" "RenderType"="Opaque" }
   
   
        SubShader {
       
            // Horizontal blur
            GrabPass {                     
                Tags { "LightMode" = "Always" }
            }
            Pass {
                Tags { "LightMode" = "Always" }
               
                CGPROGRAM
                #pragma vertex vert
                #pragma fragment frag
                #pragma fragmentoption ARB_precision_hint_fastest
                #include "UnityCG.cginc"
               
                struct appdata_t {
                    float4 vertex : POSITION;
                    float2 texcoord: TEXCOORD0;
                };
               
                struct v2f {
                    float4 vertex : POSITION;
                    float4 uvgrab : TEXCOORD0;
                };
               
                v2f vert (appdata_t v) {
                    v2f o;
                    o.vertex = UnityObjectToClipPos(v.vertex);
                    #if UNITY_UV_STARTS_AT_TOP
                    float scale = -1.0;
                    #else
                    float scale = 1.0;
                    #endif
                    o.uvgrab.xy = (float2(o.vertex.x, o.vertex.y*scale) + o.vertex.w) * 0.5;
                    o.uvgrab.zw = o.vertex.zw;
                    return o;
                }
               
                sampler2D _GrabTexture;
                float4 _GrabTexture_TexelSize;
                float _Size;
               
                half4 frag( v2f i ) : COLOR {
//                  half4 col = tex2Dproj( _GrabTexture, UNITY_PROJ_COORD(i.uvgrab));
//                  return col;
                   
                    half4 sum = half4(0,0,0,0);
 
                    #define GRABPIXEL(weight,kernelx) tex2Dproj( _GrabTexture, UNITY_PROJ_COORD(float4(i.uvgrab.x + _GrabTexture_TexelSize.x * kernelx*_Size, i.uvgrab.y, i.uvgrab.z, i.uvgrab.w))) * weight
 
                    sum += GRABPIXEL(0.05, -4.0);
                    sum += GRABPIXEL(0.09, -3.0);
                    sum += GRABPIXEL(0.12, -2.0);
                    sum += GRABPIXEL(0.15, -1.0);
                    sum += GRABPIXEL(0.18,  0.0);
                    sum += GRABPIXEL(0.15, +1.0);
                    sum += GRABPIXEL(0.12, +2.0);
                    sum += GRABPIXEL(0.09, +3.0);
                    sum += GRABPIXEL(0.05, +4.0);
                   
                    return sum;
                }
                ENDCG
            }
 
            // Vertical blur
            GrabPass {                         
                Tags { "LightMode" = "Always" }
            }
            Pass {
                Tags { "LightMode" = "Always" }
               
                CGPROGRAM
                #pragma vertex vert
                #pragma fragment frag
                #pragma fragmentoption ARB_precision_hint_fastest
                #include "UnityCG.cginc"
               
                struct appdata_t {
                    float4 vertex : POSITION;
                    float2 texcoord: TEXCOORD0;
                };
               
                struct v2f {
                    float4 vertex : POSITION;
                    float4 uvgrab : TEXCOORD0;
                };
               
                v2f vert (appdata_t v) {
                    v2f o;
                    o.vertex = UnityObjectToClipPos(v.vertex);
                    #if UNITY_UV_STARTS_AT_TOP
                    float scale = -1.0;
                    #else
                    float scale = 1.0;
                    #endif
                    o.uvgrab.xy = (float2(o.vertex.x, o.vertex.y*scale) + o.vertex.w) * 0.5;
                    o.uvgrab.zw = o.vertex.zw;
                    return o;
                }
               
                sampler2D _GrabTexture;
                float4 _GrabTexture_TexelSize;
                float _Size;
               
                half4 frag( v2f i ) : COLOR {
//                  half4 col = tex2Dproj( _GrabTexture, UNITY_PROJ_COORD(i.uvgrab));
//                  return col;
                   
                    half4 sum = half4(0,0,0,0);
 
                    #define GRABPIXEL(weight,kernely) tex2Dproj( _GrabTexture, UNITY_PROJ_COORD(float4(i.uvgrab.x, i.uvgrab.y + _GrabTexture_TexelSize.y * kernely*_Size, i.uvgrab.z, i.uvgrab.w))) * weight
 
                    //G(X) = (1/(sqrt(2*PI*deviation*deviation))) * exp(-(x*x / (2*deviation*deviation)))
                   
                    sum += GRABPIXEL(0.05, -4.0);
                    sum += GRABPIXEL(0.09, -3.0);
                    sum += GRABPIXEL(0.12, -2.0);
                    sum += GRABPIXEL(0.15, -1.0);
                    sum += GRABPIXEL(0.18,  0.0);
                    sum += GRABPIXEL(0.15, +1.0);
                    sum += GRABPIXEL(0.12, +2.0);
                    sum += GRABPIXEL(0.09, +3.0);
                    sum += GRABPIXEL(0.05, +4.0);
                   
                    return sum;
                }
                ENDCG
            }
           
            // Distortion
            GrabPass {                         
                Tags { "LightMode" = "Always" }
            }
            Pass {
                Tags { "LightMode" = "Always" }
               
                CGPROGRAM
                #pragma vertex vert
                #pragma fragment frag
                #pragma fragmentoption ARB_precision_hint_fastest
                #include "UnityCG.cginc"
               
                struct appdata_t {
                    float4 vertex : POSITION;
                    float2 texcoord: TEXCOORD0;
                };
               
                struct v2f {
                    float4 vertex : POSITION;
                    float4 uvgrab : TEXCOORD0;
                    float2 uvbump : TEXCOORD1;
                    float2 uvmain : TEXCOORD2;
                };
               
                float _BumpAmt;
                float4 _BumpMap_ST;
                float4 _MainTex_ST;
               
                v2f vert (appdata_t v) {
                    v2f o;
                    o.vertex = UnityObjectToClipPos(v.vertex);
                    #if UNITY_UV_STARTS_AT_TOP
                    float scale = -1.0;
                    #else
                    float scale = 1.0;
                    #endif
                    o.uvgrab.xy = (float2(o.vertex.x, o.vertex.y*scale) + o.vertex.w) * 0.5;
                    o.uvgrab.zw = o.vertex.zw;
                    o.uvbump = TRANSFORM_TEX( v.texcoord, _BumpMap );
                    o.uvmain = TRANSFORM_TEX( v.texcoord, _MainTex );
                    return o;
                }
               
                fixed4 _Color;
                sampler2D _GrabTexture;
                float4 _GrabTexture_TexelSize;
                sampler2D _BumpMap;
                sampler2D _MainTex;
               
                half4 frag( v2f i ) : COLOR {
                    // calculate perturbed coordinates
                    half2 bump = UnpackNormal(tex2D( _BumpMap, i.uvbump )).rg; // we could optimize this by just reading the x  y without reconstructing the Z
                    float2 offset = bump * _BumpAmt * _GrabTexture_TexelSize.xy;
                    i.uvgrab.xy = offset * i.uvgrab.z + i.uvgrab.xy;
                   
                    half4 col = tex2Dproj( _GrabTexture, UNITY_PROJ_COORD(i.uvgrab));
                    half4 tint = tex2D( _MainTex, i.uvmain ) * _Color;
                   
                    return col * tint;
                }
                ENDCG
            }
        }
    }
}