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# Source code for examples.arrows

    import sys

    import pygame
    from pygame.locals import *
    from pygame.color import *

    import pymunk
    from pymunk.vec2d import Vec2d
    from pymunk.pygame_util import draw_space, from_pygame

    def create_arrow():
        vs = [(-30,0), (0,3), (10,0), (0,-3)]
        mass = 1
        moment = pymunk.moment_for_poly(mass, vs)
        arrow_body = pymunk.Body(mass, moment)

        arrow_shape = pymunk.Poly(arrow_body, vs)
        arrow_shape.friction = .5
        arrow_shape.collision_type = 1
        return arrow_body, arrow_shape

    def stick_arrow_to_target(arrow_body, target_body, position, space):
        pivot_joint = pymunk.PivotJoint(arrow_body, target_body, position)
        phase = target_body.angle - arrow_body.angle
        gear_joint = pymunk.GearJoint(arrow_body, target_body,phase,1)
        space.add(pivot_joint)
        space.add(gear_joint)

    def post_solve_arrow_hit(space, arbiter):
        if arbiter.total_impulse.length > 300:
            a,b = arbiter.shapes
            position = arbiter.contacts[0].position
            b.collision_type = 0
            b.group = 1
            other_body = a.body
            arrow_body = b.body
            space.add_post_step_callback(stick_arrow_to_target, arrow_body, other_body, position, space)

    width, height = 800,600
    def main():
        ### PyGame init
        pygame.init()
        screen = pygame.display.set_mode((width,height))
        clock = pygame.time.Clock()
        running = True
        font = pygame.font.SysFont("Arial", 16)

        ### Physics stuff
        space = pymunk.Space()
        space.gravity = 0,-1000
        # walls - the left-top-right walls
        static= [pymunk.Segment(space.static_body, (50, 50), (50, 550), 5)
                    ,pymunk.Segment(space.static_body, (50, 550), (750, 550), 5)
                    ,pymunk.Segment(space.static_body, (750, 550), (750, 50), 5)
                    ,pymunk.Segment(space.static_body, (50, 50), (750, 50), 5)
                    ]

        b2 = pymunk.Body()
        static.append(pymunk.Circle(b2, 30))
        b2.position = 300,400

        for s in static:
            s.friction = 1.
            s.group = 1
        space.add_static(static)

        # "Cannon" that can fire arrows
        cannon_body = pymunk.Body(pymunk.inf, pymunk.inf)
        cannon_shape = pymunk.Circle(cannon_body, 25)
        cannon_shape.sensor = True
        cannon_body.position = 100,100
        space.add(cannon_shape)

        arrow_body,arrow_shape = create_arrow()
        space.add(arrow_shape)

        space.add_collision_handler(0, 1, post_solve=post_solve_arrow_hit)

        flying_arrows = []

        while running:
            for event in pygame.event.get():
                if event.type == QUIT or \
                    event.type == KEYDOWN and (event.key in [K_ESCAPE, K_q]):
                    running = False
                elif event.type == pygame.MOUSEBUTTONDOWN and event.button == 1:
                    start_time = pygame.time.get_ticks()

                elif event.type == pygame.MOUSEBUTTONUP and event.button == 1:
                    end_time = pygame.time.get_ticks()

                    diff = end_time - start_time
                    power = max(min(diff, 1000), 10) * 1.5
                    impulse = power * Vec2d(1,0)
                    arrow_body.apply_impulse(impulse.rotated(arrow_body.angle))

                    space.add(arrow_body)
                    flying_arrows.append(arrow_body)

                    arrow_body, arrow_shape = create_arrow()
                    space.add(arrow_shape)

            keys = pygame.key.get_pressed()

            speed = 2.5
            if (keys[K_UP]):
                cannon_body.position += Vec2d(0,1) * speed
            if (keys[K_DOWN]):
                cannon_body.position += Vec2d(0,-1) * speed
            if (keys[K_LEFT]):
                cannon_body.position += Vec2d(-1,0) * speed
            if (keys[K_RIGHT]):
                cannon_body.position += Vec2d(1,0) * speed

            mouse_position = from_pygame( Vec2d(pygame.mouse.get_pos()), screen )
            cannon_body.angle = (mouse_position - cannon_body.position).angle
            # move the unfired arrow together with the cannon
            arrow_body.position = cannon_body.position + Vec2d(cannon_shape.radius + 40, 0).rotated(cannon_body.angle)
            arrow_body.angle = cannon_body.angle

            for flying_arrow in flying_arrows:
                drag_constant = 0.0002
                pointing_direction = Vec2d(1,0).rotated(flying_arrow.angle)
                flight_direction = Vec2d(flying_arrow.velocity)
                flight_speed = flight_direction.normalize_return_length()
                dot = flight_direction.dot(pointing_direction)
                drag_force_magnitude = (1-abs(dot)) * flight_speed **2 * drag_constant * flying_arrow.mass

                arrow_tail_position = Vec2d(-50, 0).rotated(flying_arrow.angle)
                flying_arrow.apply_impulse(drag_force_magnitude * -flight_direction, arrow_tail_position)

                flying_arrow.angular_velocity *= 0.9

            ### Clear screen
            screen.fill(pygame.color.THECOLORS["black"])

            ### Draw stuff
            draw_space(screen, space)

            # Power meter
            if pygame.mouse.get_pressed()[0]:
                current_time = pygame.time.get_ticks()
                diff = current_time - start_time
                power = max(min(diff, 1000), 10)
                h = power / 2
                pygame.draw.line(screen, pygame.color.THECOLORS["red"], (30,550), (30,550-h), 10)

            # Info and flip screen
            screen.blit(font.render("fps: " + str(clock.get_fps()), 1, THECOLORS["white"]), (0,0))
            screen.blit(font.render("Aim with mouse, hold LMB to powerup, release to fire", 1, THECOLORS["darkgrey"]), (5,height - 35))
            screen.blit(font.render("Press R to reset, ESC or Q to quit", 1, THECOLORS["darkgrey"]), (5,height - 20))

            pygame.display.flip()

            ### Update physics
            fps = 60
            dt = 1./fps
            space.step(dt)

            clock.tick(fps)

    if __name__ == '__main__':
        sys.exit(main())

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