%
% Draw an arrow
%
% * `stemslant' gives the direction of the stem's left boundary
%   (needed for brushed stems, equals "up" for straight stems)
% * `extend' is used to make the stem longer or shorter (if negative);
%   different kinds of accidentals need different values here
%
def draw_arrow (expr attach, stemwidth, stemslant, extend, pointingdown) =
begingroup;
	save htip;  % tip height
	save wwing; % wing `radius'
	save angle_wing_bot, angle_wing_top, angle_tip;
	save upshift;
	clearxy;

	wwing := 0.26 stemwidth;
	htip := staff_space * 0.85 + stafflinethickness - wwing;

	% `flip' is used to reflect the arrow vertically
	% if arrow points downward
	transform flip;
	if pointingdown:
		flip = identity reflectedabout (origin, right);
	else:
		flip = identity;
	fi;

	z1 = attach shifted (-stemwidth / 2, 0);
	upshift := max (0, wwing + 0.1 staff_space + extend);
	z2 = z1 shifted (((unitvector stemslant)
			  scaled upshift) transformed flip);

	z7 = attach shifted ((stemwidth/2),0);
	z6 = z7 shifted (((unitvector (-xpart stemslant, ypart stemslant))
			  scaled upshift) transformed flip);
	z2 - z3 = ( 0.38 staff_space, 0.05 htip) transformed flip;
	z6 - z5 = (-0.38 staff_space, 0.05 htip) transformed flip;

	z4 = attach shifted ((-0.2 stemwidth, upshift + htip)
			     transformed flip);
	z4'= attach shifted (( 0.2 stemwidth, upshift + htip)
			     transformed flip);

	% `angle_wing_bot' is the angle at which the arc
	% from z2 to z3a enters z3a
	% `angle_wing_top' is the angle at which the arc
	% from z3b to z4 leaves z3b
	% `angle_tip' is the angle at which the arc
	% from z4 to z4' leaves z4
	angle_wing_bot = 30;
	angle_wing_top = 55;
	angle_tip = 68;

	z3a = z3 shifted ((((dir angle_wing_bot) rotated -90)
			   scaled wwing) transformed flip);
	z3b = z3 shifted ((((dir angle_wing_top) rotated 90)
			   scaled wwing) transformed flip);

	z5a = z5 shifted ((((dir (180 - angle_wing_bot)) rotated 90)
			   scaled wwing) transformed flip);
	z5b = z5 shifted ((((dir (180 - angle_wing_top)) rotated -90)
			   scaled wwing) transformed flip);

	% Draw the arrow
	pickup pencircle scaled 1;
	fill z1
	     -- z2{stemslant transformed flip}
	     .. {(-dir angle_wing_bot) transformed flip}z3a
	     .. z3b{(dir angle_wing_top) transformed flip}
	     .. z4{(dir angle_tip) transformed flip}
	     .. z4'{(dir (-angle_tip)) transformed flip}
	     .. {(dir (-angle_wing_top)) transformed flip}z5b
	     .. z5a{(-dir (-angle_wing_bot)) transformed flip}
	     .. z6{((-stemslant) reflectedabout (origin, up)) transformed flip}
	     -- z7
	     -- cycle;

	labels (range 0 thru 7, 4', 3a, 3b, 5a, 5b);
endgroup;
enddef;