Shader "Unity Shaders Book/Chapter 5/Simple Shader" {
    Properties {
        // 声明一个Color类型的属性
        _Color ("Color Tint", Color) = (1.0,1.0,1.0,1.0)
    }
    SubShader {
        Pass {
            CGPROGRAM

            #pragma vertex vert
            #pragma fragment frag

            // 在Cg代码中，我们需要定义一个与属性名称和类型都匹配的变量
            fixed4 _Color;

            // 使用一个结构体来定义顶点着色器的输入
            struct a2v {
                // POSITION语义告诉Unity，用模型空间的顶点坐标填充vertex变量
                float4 vertex : POSITION;
                // NORMAL语义告诉Unity，用模型空间的法线方向填充normal变量
                float3 normal : NORMAL;
                // TEXCOORD0语义告诉Unity，用模型的第一套纹理坐标填充texcoord变量
                float4 texcoord : TEXCOORD0;
            };

            // 使用一个结构体来定义顶点着色器的输出
            struct v2f {
                // SV_POSITION语义告诉Unity，pos里包含了顶点在裁剪空间中的位置信息
                float4 pos : SV_POSITION;
                // COLOR0语义可以用于存储颜色信息
                fixed3 color : COLOR0;
            };

            v2f vert(a2v v) : SV_POSITION {
                v2f o;
                // 使用v.vertex来访问模型空间的顶点坐标
                o.pos = mul(UNITY_MATRIX_MVP, v.vertex);
                o.color = v.normal * 0.5 + fixed3(0.5, 0.5, 0.5);
                return o;
            }

            fixed4 frag(v2f i) : SV_Target {
                fixed3 c = i.color;
                // 使用_Color属性来控制输出颜色
                c *= _Color.rgb;
                return fixed4(c, 1.0);
            }

            ENDCG
        }
    }
}

// 内部实现也是用UnityWorldSpaceViewDir
// Computes world space view direction, from object space position
// *Legacy* Please use UnityWorldSpaceViewDir instead
inline float3 WorldSpaceViewDir( in float4 localPos )
{
    float3 worldPos = mul(unity_ObjectToWorld, localPos).xyz;
    return UnityWorldSpaceViewDir(worldPos);
}

// Computes world space view direction, from object space position
inline float3 UnityWorldSpaceViewDir( in float3 worldPos )
{
    return _WorldSpaceCameraPos.xyz - worldPos;
}

// Computes object space view direction
inline float3 ObjSpaceViewDir( in float4 v )
{
    float3 objSpaceCameraPos = mul(unity_WorldToObject, float4(_WorldSpaceCameraPos.xyz, 1)).xyz;
    return objSpaceCameraPos - v.xyz;
}

// Computes world space light direction, from object space position
// *Legacy* Please use UnityWorldSpaceLightDir instead
inline float3 WorldSpaceLightDir( in float4 localPos )
{
    float3 worldPos = mul(unity_ObjectToWorld, localPos).xyz;
    return UnityWorldSpaceLightDir(worldPos);
}

// Computes world space light direction, from world space position
inline float3 UnityWorldSpaceLightDir( in float3 worldPos )
{
    #ifndef USING_LIGHT_MULTI_COMPILE
        return _WorldSpaceLightPos0.xyz - worldPos * _WorldSpaceLightPos0.w;
    #else
        #ifndef USING_DIRECTIONAL_LIGHT
        return _WorldSpaceLightPos0.xyz - worldPos;
        #else
        return _WorldSpaceLightPos0.xyz;
        #endif
    #endif
}

// 内部实现也是用UnityWorldSpaceViewDir
// Computes world space view direction, from object space position
// *Legacy* Please use UnityWorldSpaceViewDir instead
inline float3 WorldSpaceViewDir( in float4 localPos )
{
    float3 worldPos = mul(unity_ObjectToWorld, localPos).xyz;
    return UnityWorldSpaceViewDir(worldPos);
}

// Computes world space view direction, from object space position
inline float3 UnityWorldSpaceViewDir( in float3 worldPos )
{
    return _WorldSpaceCameraPos.xyz - worldPos;
}

// Computes object space view direction
inline float3 ObjSpaceViewDir( in float4 v )
{
    float3 objSpaceCameraPos = mul(unity_WorldToObject, float4(_WorldSpaceCameraPos.xyz, 1)).xyz;
    return objSpaceCameraPos - v.xyz;
}

// Computes world space light direction, from object space position
// *Legacy* Please use UnityWorldSpaceLightDir instead
inline float3 WorldSpaceLightDir( in float4 localPos )
{
    float3 worldPos = mul(unity_ObjectToWorld, localPos).xyz;
    return UnityWorldSpaceLightDir(worldPos);
}

// Computes world space light direction, from world space position
inline float3 UnityWorldSpaceLightDir( in float3 worldPos )
{
    #ifndef USING_LIGHT_MULTI_COMPILE
        return _WorldSpaceLightPos0.xyz - worldPos * _WorldSpaceLightPos0.w;
    #else
        #ifndef USING_DIRECTIONAL_LIGHT
        return _WorldSpaceLightPos0.xyz - worldPos;
        #else
        return _WorldSpaceLightPos0.xyz;
        #endif
    #endif
}