#version 120
#extension GL_EXT_geometry_shader4: enable

uniform float FpLevel;
uniform float Radius;

varying float LightIntensity;

vec3 V0, V01, V02;

void
ProduceVertex( float s, float t )
{
	const vec3 lightPos = vec3( 0., 10., 0. );

	vec3 v = V0 + s*V01 + t*V02;
	v = normalize(v);
	vec3 n = v;
	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;

	gl_Position = gl_ProjectionMatrix * ECposition;
	EmitVertex();
}



void
main()
{
	V01 = ( gl_PositionIn[1] - gl_PositionIn[0] ).xyz;
	V02 = ( gl_PositionIn[2] - gl_PositionIn[0] ).xyz;
	V0  =   gl_PositionIn[0].xyz;

	int level = int( FpLevel );
	// int numLayers = int(  pow( 2., float(level) ) );
	int numLayers = 1 << level;

	float dt = 1. / float( numLayers );

	float t_top = 1.;

	for( int it = 0; it < numLayers; it++ )
	{
		float t_bot = t_top - dt;
		float smax_top = 1. - t_top;
		float smax_bot = 1. - t_bot;

		int nums = it + 1;
		float ds_top = smax_top / float( nums - 1 );
		float ds_bot = smax_bot / float( nums );

		float s_top = 0.;
		float s_bot = 0.;

		for( int is = 0; is < nums; is++ )
		{
			ProduceVertex( s_bot, t_bot );
			ProduceVertex( s_top, t_top );
			s_top += ds_top;
			s_bot += ds_bot;
		}

		ProduceVertex( s_bot, t_bot );
		EndPrimitive();

		t_top = t_bot;
		t_bot -= dt;
	}
}