// Each #kernel tells which function to compile; you can have many kernels
#pragma kernel Clear3D

// Create a RenderTexture with enableRandomWrite flag and set it
// with cs.SetTexture
RWTexture3D<half4> _Source;
uint4 _SourceDim;
half4 _ClearColor;

[numthreads(4,4,4)]
void Clear3D (uint3 id : SV_DispatchThreadID)
{
    if (all(id.xyz < _SourceDim.xyz))
    {
        _Source[id.xyz] = _ClearColor;
    }
}