#pragma kernel CSMain
#define NUM_THREADS 8

float4 _Size;

RWStructuredBuffer<float3> _Write;
StructuredBuffer<float3> _Velocity;

[numthreads(NUM_THREADS,NUM_THREADS,NUM_THREADS)]
void CSMain (int3 id : SV_DispatchThreadID)
{

    int idxL = max(0, id.x-1) + id.y*_Size.x + id.z*_Size.x*_Size.y;
    int idxR = min(_Size.x-1, id.x+1) + id.y*_Size.x + id.z*_Size.x*_Size.y;
    
    int idxB = id.x + max(0, id.y-1)*_Size.x + id.z*_Size.x*_Size.y;
    int idxT = id.x + min(_Size.y-1, id.y+1)*_Size.x + id.z*_Size.x*_Size.y;
    
    int idxD = id.x + id.y*_Size.x + max(0, id.z-1)*_Size.x*_Size.y;
    int idxU = id.x + id.y*_Size.x + min(_Size.z-1, id.z+1)*_Size.x*_Size.y;

	float3 L = _Velocity[ idxL ];
    float3 R = _Velocity[ idxR ];
    
    float3 B = _Velocity[ idxB ];
    float3 T = _Velocity[ idxT ];
    
    float3 D = _Velocity[ idxD ];
    float3 U = _Velocity[ idxU ];
    
    float3 vorticity = 0.5 * float3( (( T.z - B.z ) - ( U.y - D.y )) , (( U.x - D.x ) - ( R.z - L.z )) , (( R.y - L.y ) - ( T.x - B.x )) );
			
	int idx = id.x + id.y*_Size.x + id.z*_Size.x*_Size.y;
	
    _Write[idx] = vorticity;
}