[Unity3D]Shader编程之腐蚀消失

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本片shader实现的效果是模型腐蚀消失，且腐蚀的边缘大小可以调、颜色可调。效果图如下：

设置面板如下：

使用时需要给ClipMask参数给一张噪点图，设置合适的cliplinesize和cliplinecolor，然后调整clipalpha就可以了。

原理是通过获取噪点图上对应的颜色，转换成灰度，然后用灰度与clipalpha对比，如果大于则被剪裁掉。

shader实现如下：

Shader "XM/CorrosionEffect" {
    Properties {
        _Color ("Color", Color) = (1,1,1,1)
        _MainTex ("Albedo (RGB)", 2D) = "white" {}
        _Glossiness ("Smoothness", Range(0,1)) = 0.5
        _Metallic ("Metallic", Range(0,1)) = 0.0
        _ClipMaskTex ("Clip Mask", 2D) = "white" {}
        _ClipGray ("Clip Alpha", Range(0.0,1.0)) = 0.0
        _ClipLineSize ("Clip Line Size", Range(0,1)) = 0.0
        _ClipLineColor("Clip Line Color", Color) = (1,1,1,1)
    }
    SubShader {
        Tags { "RenderType"="Opaque" }
        LOD 200

        CGPROGRAM
        // Physically based Standard lighting model, and enable shadows on all light types
        #pragma surface surf Standard fullforwardshadows

        // Use shader model 3.0 target, to get nicer looking lighting
        #pragma target 3.0

        sampler2D _MainTex;
        sampler2D _ClipMaskTex;

        struct Input {
            float2 uv_MainTex;
        };

        half _Glossiness;
        half _Metallic;
        fixed4 _Color;
        fixed _ClipGray;
        fixed _ClipLineSize;
        fixed4 _ClipLineColor;

        void surf (Input IN, inout SurfaceOutputStandard o) {
            fixed4 m = tex2D (_ClipMaskTex, IN.uv_MainTex);
            fixed gray = Luminance(m.rgb);
            if(gray >= _ClipGray)
            {
                clip(-1);
            }

            fixed4 c;
            if(gray >= _ClipGray - _ClipLineSize)
            {
                c = _ClipLineColor;
            }
            else
            {
                // Albedo comes from a texture tinted by color
                c = tex2D (_MainTex, IN.uv_MainTex) * _Color;
            }

            o.Albedo = c.rgb;

            // Metallic and smoothness come from slider variables
            o.Metallic = _Metallic;
            o.Smoothness = _Glossiness;
            o.Alpha = c.a;
        }
        ENDCG
    }
    FallBack "Diffuse"
}