// Vertex program to wave some grass about
// Simplistic, assumes base of the grass at 0
void grass_vp(float4 position : POSITION,
			  float3 normal   : NORMAL,
			  float2 uv		  : TEXCOORD0,
			  out float4 oPosition : POSITION,
			  out float2 oUv	   : TEXCOORD0,
			  out float4 colour    : COLOR,

			  uniform float4x4 worldViewProj,
			  uniform float4 ambient,
			  uniform float4 objSpaceLight,
			  uniform float4 lightColour,
			  uniform float4 offset)
{
	float4 mypos = position;
	//offset = float4(0.5, 0, 0, 0);
	float4 factor = float4(1,1,1,1) - uv.yyyy;
	mypos = mypos + offset * factor;
	oPosition = mul(worldViewProj, mypos);

	oUv = uv;
	// get vertex light direction (support directional and point)
	float3 light = normalize(
		objSpaceLight.xyz -  (position.xyz * objSpaceLight.w));
	float diffuseFactor = max(dot(normal, light), 0);
	
	
	colour = ambient + diffuseFactor * lightColour;
}