float smoothstep(float a, float b, float x)
{
    float t = saturate((x - a)/(b - a));
    return t*t*(3.0 - (2.0*t));
}
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struct appdata_base {
    float4 vertex : POSITION;
    float3 normal : NORMAL;
    float4 texcoord : TEXCOORD0;
    UNITY_VERTEX_INPUT_INSTANCE_ID
};

struct appdata_tan {
    float4 vertex : POSITION;
    float4 tangent : TANGENT;
    float3 normal : NORMAL;
    float4 texcoord : TEXCOORD0;
    UNITY_VERTEX_INPUT_INSTANCE_ID
};

struct appdata_full {
    float4 vertex : POSITION;
    float4 tangent : TANGENT;
    float3 normal : NORMAL;
    float4 texcoord : TEXCOORD0;
    float4 texcoord1 : TEXCOORD1;
    float4 texcoord2 : TEXCOORD2;
    float4 texcoord3 : TEXCOORD3;
    fixed4 color : COLOR;
    UNITY_VERTEX_INPUT_INSTANCE_ID
};
struct appdata_img
{
    float4 vertex : POSITION;
    half2 texcoord : TEXCOORD0;
    UNITY_VERTEX_INPUT_INSTANCE_ID
};
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struct v2f_img
{
    float4 pos : SV_POSITION;
    half2 uv : TEXCOORD0;
    UNITY_VERTEX_INPUT_INSTANCE_ID
    UNITY_VERTEX_OUTPUT_STEREO
};
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#ifndef UNITY_CG_INCLUDED
#define UNITY_CG_INCLUDED

#define UNITY_PI            3.14159265359f       //圆周率
#define UNITY_TWO_PI        6.28318530718f       //2倍圆周率
#define UNITY_FOUR_PI       12.56637061436f      //4倍圆周率
#define UNITY_INV_PI        0.31830988618f       //圆周率的倒数
#define UNITY_INV_TWO_PI    0.15915494309f       //2倍圆周率的倒数
#define UNITY_INV_FOUR_PI   0.07957747155f       //4倍圆周率的倒数
#define UNITY_HALF_PI       1.57079632679f       //半圆周率
#define UNITY_INV_HALF_PI   0.636619772367f      //半圆周率的倒数

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Shader "Unlit/Screen Position"
{
    Properties
    {
        _MainTex ("Texture", 2D) = "white" {}
    }
    SubShader
    {
        Pass
        {
            CGPROGRAM
            #pragma vertex vert
            #pragma fragment frag
            #pragma target 3.0

            // 注意：此结构中没有 SV_POSITION
            struct v2f {
                float2 uv : TEXCOORD0;
            };

            v2f vert (
                float4 vertex : POSITION, // 顶点位置输入
                float2 uv : TEXCOORD0, // 纹理坐标输入
                out float4 outpos : SV_POSITION // 裁剪空间位置输出
                )
            {
                v2f o;
                o.uv = uv;
                outpos = UnityObjectToClipPos(vertex);
                return o;
            }

            sampler2D _MainTex;

            fixed4 frag (v2f i, UNITY_VPOS_TYPE screenPos : VPOS) : SV_Target
            {
                // screenPos.xy 将包含像素整数坐标。
                // 使用它们来实现一个跳过渲染 4x4 像素块的
                // 棋盘图案

                // 棋盘图案中 4x4 像素块的 checker 值
                // 为负
                screenPos.xy = floor(screenPos.xy * 0.25) * 0.5;
                float checker = -frac(screenPos.r + screenPos.g);

                // 如果值为负，则 clip HLSL 指令停止渲染像素
                clip(checker);

                // 对于保留的像素，读取纹理并将其输出
                fixed4 c = tex2D (_MainTex, i.uv);
                return c;
            }
            ENDCG
        }
    }
}
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Shader "Unlit/Face Orientation"
{
    Properties
    {
        _ColorFront ("Front Color", Color) = (1,0.7,0.7,1)
        _ColorBack ("Back Color", Color) = (0.7,1,0.7,1)
    }
    SubShader
    {
        Pass
        {
            Cull Off // 关闭背面剔除

            CGPROGRAM
            #pragma vertex vert
            #pragma fragment frag
            #pragma target 3.0

            float4 vert (float4 vertex : POSITION) : SV_POSITION
            {
                return UnityObjectToClipPos(vertex);
            }

            fixed4 _ColorFront;
            fixed4 _ColorBack;

            fixed4 frag (fixed facing : VFACE) : SV_Target
            {
                // 正面的 VFACE 输入为正，
                // 背面的为负。根据这种情况
                // 输出两种颜色中的一种。
                return facing > 0 ?_ColorFront : _ColorBack;
            }
            ENDCG
        }
    }
}
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Shader "Unlit/VertexID"
{
    SubShader
    {
        Pass
        {
            CGPROGRAM
            #pragma vertex vert
            #pragma fragment frag
            #pragma target 3.5

            struct v2f {
    			fixed4 color : TEXCOORD0;
                float4 pos : SV_POSITION;
            };

            v2f vert (
                float4 vertex : POSITION, // 顶点位置输入
                uint vid : SV_VertexID // 顶点 ID，必须为 uint
                )
            {
                v2f o;
                o.pos = UnityObjectToClipPos(vertex);
                // 基于顶点 ID 输出时髦颜色
                float f = (float)vid;
                o.color = half4(sin(f/10),sin(f/100),sin(f/1000),0) * 0.5 + 0.5;
                return o;
            }

            fixed4 frag (v2f i) : SV_Target
            {
    			return i.color;
            }
            ENDCG
        }
    }
}

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