shader中的广告板技术

Shader "CM/Billboard1"
{
	Properties
	{
		_MainTex ("Texture", 2D) = "white" {}
	}
	SubShader
	{
		Pass
		{
			CGPROGRAM
			#pragma vertex vert
			#pragma fragment frag
			#include "UnityCG.cginc"

			struct appdata
			{
				float4 vertex : POSITION;
				float2 uv : TEXCOORD0;
			};

			struct v2f
			{
				float4 pos : SV_POSITION;
				float2 uv : TEXCOORD0;
			};

			sampler2D _MainTex;
			float4 _MainTex_ST;

			float4 Billboard(float4 vertex)
			{
				float4 ori=mul(UNITY_MATRIX_MV, float4(0,0,0,1));
				float4 vt = vertex;
				float2 r1=float2(_Object2World[0][0],_Object2World[0][2]);
				float2 r2=float2(_Object2World[2][0],_Object2World[2][2]);
				vt.xy = vt.x*r1 + vt.z*r2;
				vt.z = 0;
				vt.xyz += ori.xyz;
				return mul(UNITY_MATRIX_P, vt);
			}

			v2f vert (appdata_base v)
			{
				v2f o;
				o.pos = Billboard(v.vertex);
				return o;
			}

			fixed4 frag(v2f i) : COLOR
			{
				return tex2D(_MainTex, i.uv);
			}
			ENDCG
		}
	}
}

跟着相机转的plane:

广告板技术之二：   来自wiki ----------- https://en.wikibooks.org/wiki/Cg_Programming/Unity/Billboards            不过这种技术不能缩放广告板

Shader "Cg  shader for billboards" {
   Properties {
      _MainTex ("Texture Image", 2D) = "white" {}
   }
   SubShader {
      Pass {
         CGPROGRAM

         #pragma vertex vert
         #pragma fragment frag 

         // User-specified uniforms
         uniform sampler2D _MainTex;        

         struct vertexInput {
            float4 vertex : POSITION;
            float4 tex : TEXCOORD0;
         };
         struct vertexOutput {
            float4 pos : SV_POSITION;
            float4 tex : TEXCOORD0;
         };

         vertexOutput vert(vertexInput input)
         {
            vertexOutput output;

            output.pos = mul(UNITY_MATRIX_P,
              mul(UNITY_MATRIX_MV, float4(0.0, 0.0, 0.0, 1.0))
              - float4(input.vertex.x, input.vertex.y, 0.0, 0.0));

            output.tex = input.tex;

            return output;
         }

         float4 frag(vertexOutput input) : COLOR
         {
            return tex2D(_MainTex, float2(input.tex.xy));
         }

         ENDCG
      }
   }
}

广告板技术三 ： 草         ---------------------- 待定