Unity3D, Hemisphere Lighting

hemisphere.shader

Shader "Custom/Hemisphere_Lighting" 
{
	Properties 
	{
		_MainTex ("Texture", 2D) = "white" {}
		_SkyColor("Sky Color",Color)=(1,1,1,1)
		_GroundColor("Ground Color",Color)=(0,0,0,1)
	}
	
	SubShader 
	{
		Pass 
		{
		CGPROGRAM
			#pragma vertex vert
			#pragma fragment frag
			#include "UnityCG.cginc"
			float4 _SkyColor;
			float4 _GroundColor;
			sampler2D _MainTex;
			
			struct v2f 
			{
				float4  pos : SV_POSITION;
				float2  uv : TEXCOORD0;
				fixed4 color : COLOR0;
			};
			
			float4 _MainTex_ST;
			
			v2f vert (appdata_base v)
			{
				v2f o;
				o.pos = mul (UNITY_MATRIX_MVP, v.vertex);
				o.uv = TRANSFORM_TEX (v.texcoord, _MainTex);
				 
				fixed3 tnorm = mul(fixed4(v.normal,1),UNITY_MATRIX_MVP);
				float costheta = dot(tnorm, fixed3(0,1,0));
				float a = 0.5 + 0.5 * costheta;
				o.color =_SkyColor*a+(1-a)*_GroundColor;
				return o;
			}
			
			half4 frag (v2f i) : COLOR
			{
				half4 texcol = tex2D (_MainTex, i.uv);
				texcol.r*=i.color.r;
				texcol.g*=i.color.g;
				texcol.b*=i.color.b;
				return texcol;
			}
		ENDCG
		}
	}
	Fallback "VertexLit"
}