python - Create a square with sides at any angle -

i trying create rotating turret. turret rotates correctly problem when make turret shoot space bar bullet isn't same size or shape @ every angle. tried using angle turret facing trig calculations , find 2 corner points needed create bullet (which circle). nothing have tried work. here code:

barrel = [260,210,270,210,270,170,260,170]  def rotatebarrel():     global angle     anglechange = 2     mountcenterx = 265     mountcentery = 215     #rotate barrel     cycle = 1     while cycle < len(barrel):         x = barrel[cycle-1]-mountcenterx         y = barrel[cycle]-mountcentery         barrel[cycle-1] = (x*math.cos(anglechange*math.pi/180)-y*math.sin(anglechange*math.pi/180))+mountcenterx         barrel[cycle] = (x*math.sin(anglechange*math.pi/180)+y*math.cos(anglechange*math.pi/180))+mountcentery         cycle += 2     angle += anglechange     if angle == 360: angle = 0     canvas.coords(barrel,barrel)     self.after(1,rotatebarrel)  def spinningshoot(event):     global angle     speed = 10     shotxpos = barrel[6]+10*(math.cos(angle*math.pi/180))     shotypos = barrel[7]-10*(math.sin(angle*math.pi/180))     cornerx = barrel[6]+10*(math.cos((90-angle)*math.pi/180))     cornery = barrel[7]-10*(math.sin((90-angle)*math.pi/180))     shot = canvas.create_oval(shotxpos,shotypos,cornerx,cornery,fill="white")     xmotion = speed*math.cos(angle*math.pi/180)     ymotion = speed*math.sin(angle*math.pi/180)      shots.append(shot)     shotspos.append(shotxpos)     shotspos.append(shotypos)     shotsmotion.append(xmotion)     shotsmotion.append(ymotion) 

it looks me shot not going centered on "barrel", calculation using (90-angle) going give angular width shot of

angle - ( 90 - angle )

which 2 * angle - 90

(ie shot wider depending on size of angle).

i have thought use (angle - 45 ) , (angle + 45 ) shot same angular width , centered on barrel.

you need increase "radius" second corner. im confused +10 , -10, not quite sure do.

probably better approach calculate "centre" of bullet , draw circle centered on it. im sure there function takes centre , radius. have

radius=10 centrex= radius  * cos ( angle * math.pi /180 ) centrey= radius * sin ( angle * math. pi / 180 ) 

and pass 2 , radius function circle

one other little thing, suggest changing line

if angle == 360: angle = 0 

to

if angle >= 360: angle = angle-360 

as if angle initialized other number or changed angle step "miss" 360 , never wrap around.