billboard Shader待研究下

 Shader "Tut/Project/Billboard_1" {
 Properties {
 _MainTex ("Base (RGB)", 2D) = "white" {}
 }
 SubShader {
 Tags { "Queue"="Transparent" "IgnoreProjector"="True" "RenderType"="Transparent" }
 pass{
 Cull Off
 ZTest Always
 Blend SrcAlpha OneMinusSrcAlpha
 CGPROGRAM
 #pragma vertex vert
 #pragma fragment frag
 #include "UnityCG.cginc"
 sampler2D _MainTex;
 struct v2f {
 float4 pos:SV_POSITION;
 float2 texc:TEXCOORD0;
 };
 v2f vert(appdata_base v)
 {
 v2f o;
 float4 ori=mul(UNITY_MATRIX_MV,float4(,,,));
 float4 vt=v.vertex;
 vt.y=vt.z;//这个平面是沿xz平面 展开的
 vt.z=;//所以只关心其平面上的信息

 //通过加上Object Space的原点在ViewSpace的信息，保持其透视大小
 vt.xyz+=ori.xyz;//result is vt.z==ori.z ,so the distance to camera keeped ,and screen size keeped
 o.pos=mul(UNITY_MATRIX_P,vt);

 o.texc=v.texcoord;
 return o;
 }
 float4 frag(v2f i):COLOR
 {
 return tex2D(_MainTex,i.texc);
 }
 ENDCG
 }//endpass
 }
 }