displacement
secondd(
	float	Height = 0.2,				// displacement height
		Ks = 0.5,				// specular coefficient
		Kd = 0.5, 				// diffuse  coefficient
		Ka = .1, 				// ambient  coefficient
		roughness = 0.1;			// specular roughness
	color	SpecularColor = color( 1, 1, 1 )	// specular color
)
{
	float RAMP = 0.2;				// over how much of the width to ramp up

	float TheHeight = 0.;			// how much displacement to apply

	float up = 2. * u;
	float vp = v;
	float WIDTH = 0.10;
	float numinu = floor( up / WIDTH );
	float numinv = floor( vp / WIDTH );
	
	if( mod( numinu+numinv, 2. ) == 0. )
	{
		float umin = numinu*WIDTH;
		float umax = umin+WIDTH;
		float vmin = numinv*WIDTH;
		float vmax = vmin+WIDTH;
		float distu = min( up-umin, umax-up );
		float distv = min( vp-vmin, vmax-vp );
		float dist = min( distu, distv )/WIDTH;
		float t = smoothstep( 0., RAMP, dist );	// 0. if dist <= 0., 1. if dist >= RAMP
		TheHeight = t*Height;				// apply the blending
	}

#define BUMP_MAPPING
	
	if( TheHeight != 0. )
	{
#ifdef BUMP_MAPPING
		N = calculatenormal( P + normalize(N) * TheHeight );
#else
		P = P + normalize(N) * TheHeight;
		N = calculatenormal(P);
#endif
	}
}