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struct World
{
	enum { search_res = 4 }; // search 4x4 points in a tile if a recusion is required
	enum { tiles_res = 2 };  // tile res : resolution of the tiles 
	enum { radius = 1 };     // planet radius

	static void draw_quad(vec3f pos, float size) 
	{
		// comment out the following line for solid rendering
		glPolygonMode(GL_FRONT_AND_BACK, GL_LINE);
		glBegin(GL_QUADS);
		loopi(0, 4)
		{
			vec3f p = pos + vec3f((i & 1) ^ (i >> 1), (i >> 1), 0)*size;
			p = p.norm() * radius;
			glVertex3f(p.x, p.y, p.z);
		}
		glEnd();
		glPolygonMode(GL_FRONT_AND_BACK, GL_FILL);		
	};
	static void draw_recursive(vec3f p, float size, vec3f center)
	{
		float tile_size = float(size) / float(tiles_res);
		float ratio		= gui.screen[0].slider["lod.ratio"].val;
		float minsize	= gui.screen[0].slider["detail"].val;

		loopi(0, tiles_res) loopj(0, tiles_res)
		{
			float a = float(i) *size / float(tiles_res) + p.x;
			float b = float(j) *size / float(tiles_res) + p.y;

			float dist = 999999;
			loopk(0, search_res + 1)	
			loopl(0, search_res + 1)
			{
				float dotp = vec3f(
					a + (float(k) / search_res)*tile_size, 
					b + (float(l) / search_res)*tile_size, p.z).norm().dot(center);
				float d = acos(dotp) / M_PI; // anlge
				dist = min(dist, d);
			}
			if (dist > 0.5) continue;//culling

			// recurse ?
			if (dist < ratio*size && size > minsize)
				draw_recursive(vec3f(a, b, p.z), tile_size, center);	// yes
			else
				draw_quad(vec3f(a, b, p.z), tile_size);					// no
		}
	};
	static void draw(vec3f center)
	{
		// center is the center of detail on the sphere
		// ||center|| = 1
		vec3f patch_start(-1, -1, -1);
		float patch_size = 2; // plane xy size

		// Draw 6 Planes

		// Front
		World::draw_recursive(patch_start, 2, center);
		// Back
		glRotatef(180, 0, 1, 0);
		World::draw_recursive(patch_start, patch_size, vec3f(-center.x, center.y, -center.z));
		glRotatef(-180, 0, 1, 0);
		// Right
		glRotatef(90, 0, 1, 0);
		World::draw_recursive(patch_start, patch_size, vec3f(-center.z, center.y, center.x));
		glRotatef(-90, 0, 1, 0);
		// Left
		glRotatef(-90, 0, 1, 0);
		World::draw_recursive(patch_start, patch_size, vec3f(center.z, center.y, -center.x));
		glRotatef(90, 0, 1, 0);
		// Up
		glRotatef(90, 1, 0, 0);
		World::draw_recursive(patch_start, patch_size, vec3f(center.x, center.z, -center.y));
		glRotatef(-90, 1, 0, 0);
		// Down
		glRotatef(-90, 1, 0, 0);
		World::draw_recursive(patch_start, patch_size, vec3f(center.x, -center.z, center.y));
		glRotatef(90, 1, 0, 0);
	}
};