Firing bullets from a rotating gun - python-2.7

Question

My question is connected to this question:
rotating gun with restricted movement
What calculations do you need to do to get bullets firing from the gun muzzle?
my code is given below
def gun_radar(self):
for p in self.gameobjects:
if "R" in p.name or "L" in p.name:
if abs(p.rect.centerx - self.hero.rect.centerx) < p.radar and abs(p.rect.centery - self.hero.rect.centery) < p.radar: # if hero within radar
p.vec_to_target = pygame.math.Vector2(self.hero.rect.center) - p.rect.center
p.direction = p.orig_direction.rotate(p.current_angle)
p.orientation = p.vec_to_target.dot(p.direction)
if p.orientation > 2:
p.current_angle += 1
elif p.orientation < -2:
p.current_angle -= 1
p.current_angle = p.clamp(p.current_angle, p.clamp_min, p.clamp_max)
p.gun_rotate(-p.current_angle)
self.blt_timer -= 1 #count down the timer. when zero calculate vector and add bullet to fired_blts
if self.blt_timer<= 0:
w, h = p.rect.center
angle_in_rad = p.current_angle * (math.pi) / 180
w = w + math.cos(angle_in_rad)
h = h + math.sin(-angle_in_rad)
bullet = Bombullet(bulletimage, w, h)
bullet.xvel = bullet.speed * math.cos(angle_in_rad)
bullet.yvel = bullet.speed * math.sin(angle_in_rad)
bullet.rect.x += bullet.xvel
bullet.rect.y += bullet.yvel
self.fired_blts.add(bullet)
self.blt_timer = 100
when the hero comes within a circular area of the gun it is activated and a bullet shoots from the center of the gun.
I move the bullet with
def move(self):
self.rect.x += self.xvel
self.rect.y += self.yvel
print self.rect.x, self.rect.y, self.life
self.life -= 1
the bullet updates and shoots in the correct direction but shoots from the center of the gun. How do I move the shooting point to the muzzle?

Answer 1

Here's an example of a firing cannon. You just have to pass the current angle and the rect.center of the cannon to the newly created bullet and then rotate its image and velocity vector in the __init__ method.
import math
import pygame as pg
from pygame.math import Vector2
pg.init()
screen = pg.display.set_mode((640, 480))
FONT = pg.font.Font(None, 24)
BLACK = pg.Color('black')
BG_COLOR = pg.Color('darkseagreen4')
class Bullet(pg.sprite.Sprite):
def __init__(self, pos, angle):
super(Bullet, self).__init__()
self.image = pg.Surface((20, 11), pg.SRCALPHA)
pg.draw.rect(self.image, pg.Color('grey11'), [0, 0, 13, 11])
pg.draw.polygon(
self.image, pg.Color('grey11'), [(13, 0), (20, 5), (13, 10)])
self.image = pg.transform.rotate(self.image, -angle)
self.rect = self.image.get_rect(center=pos)
# To apply an offset to the start position,
# create another vector and rotate it as well.
offset = Vector2(80, 0).rotate(angle)
# Use the offset to change the starting position.
self.pos = Vector2(pos) + offset
self.velocity = Vector2(5, 0)
self.velocity.rotate_ip(angle)
def update(self):
self.pos += self.velocity
self.rect.center = self.pos
def main():
clock = pg.time.Clock()
# The cannon image and rect.
surf = pg.Surface((40, 22), pg.SRCALPHA)
surf.fill(pg.Color('grey27'))
pg.draw.rect(surf, pg.Color('grey11'), [30, 6, 10, 10])
orig_surf = surf
rect = surf.get_rect(center=(320, 240))
angle = 0 # Angle of the cannon.
# Add bullets to this group.
bullet_group = pg.sprite.Group()
playing = True
while playing:
for event in pg.event.get():
if event.type == pg.QUIT:
playing = False
if event.type == pg.MOUSEBUTTONDOWN:
if event.button == 1: # Left button fires bullet.
# Fire a bullet from cannon center with current angle.
bullet_group.add(Bullet(rect.center, angle))
bullet_group.update()
# Find angle to target (mouse pos).
x, y = Vector2(pg.mouse.get_pos()) - rect.center
angle = math.degrees(math.atan2(y, x))
# Rotate the cannon image.
surf = pg.transform.rotate(orig_surf, -angle)
rect = surf.get_rect(center=rect.center)
# Draw
screen.fill(BG_COLOR)
bullet_group.draw(screen)
screen.blit(surf, rect)
txt = FONT.render('angle {:.1f}'.format(angle), True, BLACK)
screen.blit(txt, (10, 10))
pg.draw.line(
screen, pg.Color(150, 60, 20), rect.center, pg.mouse.get_pos(), 2)
pg.display.update()
clock.tick(30)
if __name__ == '__main__':
main()
pg.quit()
You can also use math.cos and sin to calculate the offset.
run = math.cos(math.radians(angle)) * 80
rise = math.sin(math.radians(angle)) * 80
offset = run, rise

Answer 2

I achieved what I needed to do with thefollowing code which is the same as above with a very slight modification which is explained in the code. #skrx answer and the comment by Nick A. aided me to achieve this.
def gun_radar(self):
for p in self.gameobjects:
if "R" in p.name or "L" in p.name:
if abs(p.rect.centerx - self.hero.rect.centerx) < p.radar and abs(p.rect.centery - self.hero.rect.centery) < p.radar: # if hero within radar
p.vec_to_target = pygame.math.Vector2(self.hero.rect.center) - p.rect.center
p.direction = p.orig_direction.rotate(p.current_angle)
p.orientation = p.vec_to_target.dot(p.direction)
if p.orientation > 2:
p.current_angle += 1
elif p.orientation < -2:
p.current_angle -= 1
p.current_angle = p.clamp(p.current_angle, p.clamp_min, p.clamp_max)
p.gun_rotate(-p.current_angle)
p.timer -= 1 #count down the timer. when zero calculate vector and add bullet to fired_blts
if p.timer<= 0:
w, h = p.rect.center
# adjust for the distance fromm the gun center to the gun muzzle
w = w + math.cos(math.radians(p.current_angle)) * 28
h = h + math.sin(math.radians(p.current_angle)) * 28
bullet = Bombullet(bulletimage, w, h) # create the bullet
# calculate the velocity
bullet.xvel = bullet.speed * math.cos(math.radians(p.current_angle))
bullet.yvel = bullet.speed * math.sin(math.radians(p.current_angle))
self.fired_blts.add(bullet)
p.timer = 100