一，使用UIRawImage,创建材质球，把Shader给材质球，放到RawImage的Material上，

// Upgrade NOTE: replaced 'mul(UNITY_MATRIX_MVP,*)' with 'UnityObjectToClipPos(*)'

Shader "UI/Default No-Alpha"
{
    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
    }

        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]
            Fog { Mode Off }
            Blend One Zero
            ColorMask[_ColorMask]
            Blend One OneMinusSrcAlpha // 源rgba*1 + 背景rgba*(1-源A值)  

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

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

                struct v2f
                {
                    float4 vertex   : SV_POSITION;
                    fixed4 color : COLOR;
                    half2 texcoord  : TEXCOORD0;
                };

                fixed4 _Color;

                v2f vert(appdata_t IN)
                {
                    v2f OUT;
                    OUT.vertex = UnityObjectToClipPos(IN.vertex);
                    OUT.texcoord = IN.texcoord;
    #ifdef UNITY_HALF_TEXEL_OFFSET  
                    OUT.vertex.xy -= (_ScreenParams.zw - 1.0);
    #endif  
                    OUT.color = IN.color * _Color;
                    return OUT;
                }

                sampler2D _MainTex;

                fixed4 frag(v2f IN) : SV_Target
                {
                    half4 color = tex2D(_MainTex, IN.texcoord) * IN.color;
                    //clip (color.a - 0.01);  
                    return color;
                }
            ENDCG
            }
        }
}