#version 120
#extension GL_EXT_geometry_shader4: enable

varying float LightIntensity;

#ifdef NOTDEF
	vec3 tnorm = normalize( gl_NormalMatrix * n );	// the transformed normal
	vec4 ECposition = gl_ModelViewMatrix * vec4( (Radius*v), 1. );
	LightIntensity  = dot( normalize(lightPos - ECposition.xyz), tnorm );
	LightIntensity = abs( LightIntensity );
	LightIntensity *= 1.5;
#endif


void
main()
{
	vec3 V0 = gl_PositionIn[0].xyz;
	vec3 V1 = gl_PositionIn[1].xyz;
	vec3 V2 = gl_PositionIn[2].xyz;
	vec3 V3 = gl_PositionIn[3].xyz;
	vec3 V4 = gl_PositionIn[4].xyz;
	vec3 V5 = gl_PositionIn[5].xyz;

	vec3 N042 = cross( V4-V0, V2-V0 );
	vec3 N021 = cross( V2-V0, V1-V0 );
	vec3 N243 = cross( V4-V2, V3-V2 );
	vec3 N405 = cross( V0-V4, V5-V4 );

	if( dot( N042, N021 ) < 0. )
		N021 = vec3(0.,0.,0.) - N021;

	if( dot( N042, N243 ) < 0. )
		N243 = vec3(0.,0.,0.) - N243;

	if( dot( N042, N405 ) < 0. )
		N405 = vec3(0.,0.,0.) - N405;


	if( N042.z * N021.z < 0. )
	{
		gl_Position = gl_ProjectionMatrix * vec4( V0, 1. );
		EmitVertex();
		gl_Position = gl_ProjectionMatrix * vec4( V2, 1. );
		EmitVertex();
		EndPrimitive();
	}

	if( N042.z * N243.z < 0. )
	{
		gl_Position = gl_ProjectionMatrix * vec4( V2, 1. );
		EmitVertex();
		gl_Position = gl_ProjectionMatrix * vec4( V4, 1. );
		EmitVertex();
		EndPrimitive();
	}

	if( N042.z * N405.z < 0. )
	{
		gl_Position = gl_ProjectionMatrix * vec4( V4, 1. );
		EmitVertex();
		gl_Position = gl_ProjectionMatrix * vec4( V0, 1. );
		EmitVertex();
		EndPrimitive();
	}
}