Barycentrics solid wireframe shader

OpenGL
1 
const vec3 vectors[3] = {
	vec3(1.0, 0.0 ,0.0),
	vec3(0.0, 1.0 ,0.0),
	vec3(0.0, 0.0 ,1.0)
};

varying vec3 barycentrics;

void vertex() {
	barycentrics = vectors[VERTEX_ID % 3];
}

void fragment() {
	vec3 dBaryCoordX = dFdx(barycentrics);
	vec3 dBaryCoordY = dFdy(barycentrics);
	vec3 dBaryCoord  = sqrt(dBaryCoordX * dBaryCoordX + dBaryCoordY * dBaryCoordY);
	vec3 Remap = smoothstep(vec3(0.0), dBaryCoord, barycentrics);
	float ClosestEdge = min(min(Remap.x, Remap.y), Remap.z);
	ALBEDO = vec3(ClosestEdge);
}

image
image746×764 123 KB

When I apply the shader to object, I am seeting weird thing that some of surfaces (mostly top/bottom) are appears as black, what can be the reason?
Is it because of wrong normal set to its surface?

Thanks,