Shader "MyUnlit/MyBillboarding"
{
    Properties
     {
         _MainTex ("Texture", 2D) = "white" {}
         _Color("Color Tint",color)=(1,1,1,1)
     }
     SubShader
     {
         //对顶点进行变换需禁用合P
         Tags{ "Queue" = "Transparent" "RenderType" = "Transparent" "IgnoreProjector" = "true" "DisableBatching" = "True" }
 
         Pass
         {
             //透明度混合
             Tags{ "lightmode" = "forwardbase" }
             ZWrite off
             Blend SrcAlpha OneMinusSrcAlpha
             Cull off
 
             CGPROGRAM
             #pragma vertex vert
             #pragma fragment frag
             #pragma multi_compile_fog
 
             #include "UnityCG.cginc"
 
             struct appdata
             {
                 float4 vertex : POSITION;
                 float2 uv : TEXCOORD0;
             };
 
             struct v2f
             {
                 float2 uv : TEXCOORD0;
                 UNITY_FOG_COORDS(1)
                 float4 vertex : SV_POSITION;
             };
 
             sampler2D _MainTex;
             float4 _MainTex_ST;
             fixed4 _Color;
 
             v2f vert (appdata v)
             {
                 v2f o;
                 //计算模型空间中的视线方向
                 float3 objViewDir = mul(unity_WorldToObject, float4(_WorldSpaceCameraPos, 1));
 
                 //计算旋转矩阵的各个基向量
                 float3 normalDir =normalize(objViewDir);
                 float3 upDir =float3(0, 1, 0);
                 float3 rightDir = normalize(cross(normalDir, upDir));
                 upDir = normalize(cross(normalDir, rightDir));
 
                 //用旋转矩阵对顶点进行偏移
                 float3 localPos =rightDir * v.vertex.x + upDir * v.vertex.y + normalDir * v.vertex.z;
 
                 //将偏移之后的值作为新的顶点传递计算
                 o.vertex = UnityObjectToClipPos(float4(localPos,1));
                 o.uv = TRANSFORM_TEX(v.uv, _MainTex);
                 UNITY_TRANSFER_FOG(o,o.vertex);
                 return o;
             }
 
             fixed4 frag (v2f i) : SV_Target
             {
                 fixed4 col = tex2D(_MainTex, i.uv);
                 col.rgb *= _Color.rgb;
                 UNITY_APPLY_FOG(i.fogCoord, col);
                 return col;
             }
             ENDCG
         }
     }
     fallback "Transparent/VertexLit"
}