how to add shadows to billboard shader help....

Thanks so much for your help Jona $$anonymous$$arklund its working fine but a slight problem it that the shadow is not at its proper place like the texture is leaving the planer's position but the shadow is rendering from the planes position

pardon me for my english here is a screen shot of what i am sayng hope its understandable thanks for looking in to the matter

Hello AR, you could try this, it allows for the mesh you have the shader attached to, to be scaled and rotated and change to look of the sprite that way.

 Shader "J$$anonymous$$/BillboardShadowCast" 
 {
 
 //Please note that this shader is made to work with the Unity3D Cube object
 //Shadows will be cast depending upon the Transform of the cube object
 //By Jona $$anonymous$$arklund 27th of August 2013
 
 Properties 
 {
     _Cutoff ("Cutoff", Range(0.0,1.0)) = 0.5
     _$$anonymous$$ainTex ("Particle Texture", 2D) = "white"
 }
  
 SubShader 
 {
 
     AlphaTest Greater [_Cutoff]
 
     Pass
     {
     Tags {  "Light$$anonymous$$ode" = "ShadowCaster" }
     SetTexture [_$$anonymous$$ainTex]
     }
  
     Pass
     {
 
     Tags { "Queue" = "AlphaTest" "RenderType"="Transparentcutout" }
 
         CGPROGRA$$anonymous$$
         #pragma vertex vert
         #pragma fragment frag
 
         struct appdata 
         {
         float4 position : POSITION;
         float4 texcoord : TEXCOORD0;
         };
 
         struct v2f 
         {
         float4 position : SV_POSITION;
         float4 texcoord : TEXCOORD0;
         };
  
         uniform sampler2D _$$anonymous$$ainTex;
 
         v2f vert(appdata IN)
         {
         v2f OUT;
  
         
 
         //Simple Version (Normal Billboard)
         //Based upon : http://en.wikibooks.org/wiki/Cg_Program$$anonymous$$g/Unity/Billboards
             /*
 
         OUT.position = mul(UNITY_$$anonymous$$ATRIX_P,
         mul(UNITY_$$anonymous$$ATRIX_$$anonymous$$V, float4(0.0, 0.0, 0.0, 1.0))
         - float4(IN.position.x, IN.position.z, 0.0, 0.0));
 
         OUT.texcoord = IN.texcoord;
             */
 
         //Complex Version (Rotates based upon Transform)
         //Based upon Lulucifer's code
         ///*
         float4 modelView = mul(UNITY_$$anonymous$$ATRIX_$$anonymous$$V,float4(0,0,0,1));
         float4 INposition = IN.position;
 
         float2 r1 = float2(_Object2World[0][0],_Object2World[0][2]);
         float2 r2 = float2(_Object2World[2][0],_Object2World[2][2]);
 
         float2 INposition0 = INposition.x*r1;
 
         INposition0 += INposition.z*r2;
         INposition.xy = INposition0;
         INposition.z = 0.0;
         INposition.xyz += modelView.xyz;
 
         OUT.position = mul(UNITY_$$anonymous$$ATRIX_P, INposition);
 
         OUT.texcoord = -IN.texcoord;
         //*/
 
         return OUT;
         }
 
         fixed4 frag(v2f IN) : COLOR
         {
  
         float4 color = tex2D(_$$anonymous$$ainTex, float2(IN.texcoord.xy));
         return color;
         }
         ENDCG
     }
 }
 }
 

its not showing the texture when i apply this shader my texture disappears suddenly dnt knw what is the problem

It's made to work with the Unity Cube object.

You may want to consider if a billboard shader is the right choice for your trees as well.

Using this simpler _cutoff / shadow shader

 Shader "J$$anonymous$$/CutoffShadowCast" 
 {
 
 //By Jona $$anonymous$$arklund 27th of August 2013
 
 Properties 
 {
     _Cutoff ("Cutoff", Range(0.0,1.0)) = 0.5
     _$$anonymous$$ainTex ("Particle Texture", 2D) = "white"
 }
  
 SubShader 
 {
 
     AlphaTest Greater [_Cutoff]
 
     Pass
     {
     Tags {  "Light$$anonymous$$ode" = "ShadowCaster" }
     SetTexture [_$$anonymous$$ainTex]
     }
  
     Pass
     {
 
     Tags { "Queue" = "AlphaTest" "RenderType"="Transparentcutout" }
 
         CGPROGRA$$anonymous$$
         #pragma vertex vert
         #pragma fragment frag
 
         struct appdata 
         {
         float4 position : POSITION;
         float4 texcoord : TEXCOORD0;
         };
 
         struct v2f 
         {
         float4 position : SV_POSITION;
         float4 texcoord : TEXCOORD0;
         };
  
         uniform sampler2D _$$anonymous$$ainTex;
 
         v2f vert(appdata IN)
         {
         v2f OUT;
  
 
         OUT.texcoord = IN.texcoord;
         OUT.position = mul(UNITY_$$anonymous$$ATRIX_$$anonymous$$VP, IN.position);
 
         return OUT;
         }
 
         fixed4 frag(v2f IN) : COLOR
         {
  
         float4 color = tex2D(_$$anonymous$$ainTex, float2(IN.texcoord.xy));
         return color;
         }
         ENDCG
     }
 }
 }

along with a script such as.

 using UnityEngine;
 using System.Collections;
 
 //Put this script on your tree objects
 
 public class ForestFacing : $$anonymous$$onoBehaviour {
 
     public Transform target;        //The target of the rotation (An example would be your camera)
     public int rotSpeed = 1;        //How quickly the trees rotate
 
     private Transform myTransform;  //Current object's transform
 
     void Awake()
     {
         myTransform = transform;
     }
 
     void Update () 
     {
 
         //Look at Player on the X and Z axis
         myTransform.rotation = Quaternion.Slerp(myTransform.rotation, Quaternion.LookRotation(new Vector3(target.position.x, 0, target.position.z) - new Vector3(myTransform.position.x, 0, myTransform.position.z)), rotSpeed * Time.deltaTime);
 
 
     }
 }

This one.