function status = stick_vis( t, x, flag, color)
% stick_vis: draw an stick figure
%	stick_vis( [], [], 'init'): prepare a frame for animation
%	stick_vis( t, x, [], color): draw a stick figure
%		x = [ th1; th2; om1; om2]
%	stick_vis( [], [], 'done'): do nothing

global	E

if ischar( t)
	flag = t;	% use first arg as flag
else
	if nargin<3, flag = '';	end	% ode standard
end

figure( E.fig(1));
l = 1.2*sum(E.L);

switch( flag)
case 'init'			% prepare animation frame
	E.hold = 0;	% clear every frame
	cla;
	axis( 'equal');
	axis( [ -l l -0.4*l l]);
	set( gca,'Box','on','XTick',[],'YTick',0,'YTickLabel','','YGrid','on');
case ''
	if E.hold == 0, cla; end
	px = cumsum( [ 0; E.L(1)*sin(x(1)); E.L(2)*sin(x(1)+x(2))]);
	py = cumsum( [ 0; E.L(1)*cos(x(1)); E.L(2)*cos(x(1)+x(2))]);
	% floor
	% line( [-l,l], [0,0]);	% or use grid line
	% stick figure
	if nargin<4, color=[0.5,0.5,0.5]; end
	line( px, py, 'LineWidth', 5, 'Color', color);
	% time
	text( 0.4*l, -0.3*l, [ 't=', num2str(t)], 'FontSize', 18);
	status = E.stop;
case 'done'
otherwise
	error( [ ' invalid option: ', flag]);
end
drawnow;