Python - Pygame bullet movements

Question

I am trying to find a way to get the rotation of the ship and apply it to the beam so that it will travel in the direction it was shot in.. I really have no idea how I would do this but here is my code: Please excuse the messiness of it, I put comments in so you know whats what.

import sys, pygame, math, time;
from pygame.locals import *;
spaceship = ('spaceship.png')
mouse_c = ('crosshair.png')
backg = ('background.jpg')
fire_beam = ('beams.png')
pygame.init()
screen = pygame.display.set_mode((800, 600))
bk = pygame.image.load(backg).convert_alpha()
mousec = pygame.image.load(mouse_c).convert_alpha()
space_ship = pygame.image.load(spaceship).convert_alpha()
f_beam = pygame.image.load(fire_beam).convert_alpha()
f_beam = pygame.transform.scale(f_beam, (50, 50))
f_beam_rect = f_beam.get_rect()
clock = pygame.time.Clock()
pygame.mouse.set_visible(False)
space_ship_rect = space_ship.get_rect()
space_ship_rect.centerx = 375
space_ship_rect.centery = 300
speed = 3.5
pressed_down = 0
while True:
    clock.tick(60)
    screen.blit(bk, (0, 0))
    for event in pygame.event.get():
        if event.type == QUIT:
            pygame.quit()
            sys.exit()
        elif event.type == MOUSEBUTTONDOWN and event.button == 3:
            pressed_down = 1
        elif event.type == MOUSEBUTTONUP:
            pressed_down = 0
        if pressed_down == 1:
            x, y = pygame.mouse.get_pos()
            x1, y1 = x - space_ship_rect.x, y - space_ship_rect.y
            angle = math.atan2(y1, x1)
            dx = speed*math.cos(angle)
            dy = speed*math.sin(angle)
            movex = space_ship_rect.centerx = space_ship_rect.centerx + dx#ship x
            movey = space_ship_rect.centery = space_ship_rect.centery + dy#ship y
        if event.type == MOUSEMOTION:
            x1, y1 = pygame.mouse.get_pos()
            x2, y2 = space_ship_rect.x, space_ship_rect.y
            dx, dy = x2 - x1, y2 - y1
            rads = math.atan2(dx, dy)
            degs = math.degrees(rads)
            display_s = pygame.transform.rotate(space_ship, (degs))#rotation of ship
        if event.type == MOUSEBUTTONDOWN and event.button == 1:
            #Is it possible for me to get the degree rotation of the space_ship and apply it to here so the beam will travel in the direction it was shot in?
    screen.blit(display_s, (space_ship_rect.centerx, space_ship_rect.centery))
    pos = pygame.mouse.get_pos()
    screen.blit(mousec, (pos))
    pygame.display.update()

Please double check the indentation before posting a code(Python spc.) I have formatted the code but I want you to ensure it. — xor
– xor, Commented Nov 24, 2013 at 15:24
You mean a laser beam is fired from a space ship and you want to fire the beam in the direction the spaceship is oriented? — xor
– xor, Commented Nov 24, 2013 at 15:26
@adil Yes, the indentation is now correct sorry about that, and yes that is what i'm looking for adil :) — user2993584
– user2993584, Commented Nov 24, 2013 at 15:35
You have spaceship angle (and dx, dy) so use it for laser beam. — furas
– furas, Commented Nov 24, 2013 at 15:42
Then why don't you just calculate the slope between your cross-hair and spaceship and also i will recommend if you attach a gun to your spaceship (a point) and use it to calculate the slope — xor
– xor, Commented Nov 24, 2013 at 15:43

furas · Accepted Answer · 2013-11-24 18:34:57Z

I see you have problem with ship rotation.

If you create rotated spaceship display_s you get image with different size than space_ship size so you have to get display_s rectangle and assign spaceship center to display_s center.

 display_s_rect = display_s.get_rect( center=spaceship_rect.center)

Now you have to use display_s_rect to display display_s

 screen.blit(display_s, display_s_rect)

By the way:

blit() expect position where to put left top corner of blited image on screen.

With

screen.blit(display_s, (space_ship_rect.centerx, space_ship_rect.centery))

left top corner of display_s will be put in (space_ship_rect.centerx, space_ship_rect.centery) but I think you want to put display_s center in (space_ship_rect.centerx, space_ship_rect.centery)

Assign center values (as before) to (space_ship_rect.centerx, space_ship_rect.centery) but use (space_ship_rect.x, space_ship_rect.y) in blit().

You can use space_ship_rect in place of (space_ship_rect.x, space_ship_rect.y) in blit() with the same result.

I think you have the same problem with mousec position in blit().

Get mousec rectangle, assign mouse position to rectangle center and than use rectangle x,y to blit.

 mousec_rect = mousec.get_rect( center = pygame.mouse.get_pos() )
 screen.blit(mousec, mousec_rect)

EDIT:

your mainloop after my modification - now ship is rotate as it should

display_s = space_ship # default value at start when ship wasn't rotate

while True:
    clock.tick(60)
    screen.blit(bk, (0, 0))
    for event in pygame.event.get():
        if event.type == QUIT:
            pygame.quit()
            sys.exit()
        elif event.type == MOUSEBUTTONDOWN and event.button == 3:
            pressed_down = 1
        elif event.type == MOUSEBUTTONUP:
            pressed_down = 0
        if pressed_down == 1:
            x, y = pygame.mouse.get_pos()
            x1, y1 = x - space_ship_rect.x, y - space_ship_rect.y
            angle = math.atan2(y1, x1)
            dx = speed*math.cos(angle)
            dy = speed*math.sin(angle)
            movex = space_ship_rect.centerx = space_ship_rect.centerx + dx#ship x
            movey = space_ship_rect.centery = space_ship_rect.centery + dy#ship y
        if event.type == MOUSEMOTION:
            x1, y1 = pygame.mouse.get_pos()
            x2, y2 = space_ship_rect.centerx, space_ship_rect.centery
            dx, dy = x2 - x1, y2 - y1
            rads = math.atan2(dx, dy)
            degs = math.degrees(rads)

            display_s = pygame.transform.rotate(space_ship, (degs))#rotation of ship
            display_s_rect = display_s.get_rect(center = space_ship_rect.center)            

        if event.type == MOUSEBUTTONDOWN and event.button == 1:
            #Is it possible for me to get the degree rotation of the space_ship and apply it to here so the beam will travel in the direction it was shot in?
            pass

    screen.blit(display_s, display_s_rect)
    #screen.blit(display_s, space_ship_rect)

    pos = pygame.mouse.get_pos()
    mousec_rect = mousec.get_rect(centerx=pos[0], centery=pos[1])

    screen.blit(mousec, mousec_rect )

    pygame.display.update()

xor · Accepted Answer · 2013-11-24 18:20:25Z

Before the While Loop:
beam_speed=<somevalue>
f_beam_rect=space_ship_rect #initialise beam position
fired=False #check if beam is fired or not

Inside While Loop

##If beam is fired(right click) blit images through-out the path
if fired:
    b_angle = math.atan2(by1, bx1)
    bdx = beam_speed*math.cos(b_angle)
    bdy = beam_speed*math.sin(b_angle)
    f_beam_rect.centerx = f_beam_rect.centerx + bdx
    f_beam_rect.centery = f_beam_rect.centery + bdy
    screen.blit(f_beam,f_beam_rect)

for event in pygame.event.get():

    if event.type == QUIT:
        pygame.quit()
        sys.exit()

###If mouse is clicked then find the direction (mouse position and spaceship)

    elif event.type == MOUSEBUTTONDOWN and event.button == 1:
        bx, by = pygame.mouse.get_pos()
        bx1, by1 = bx - space_ship_rect.x, by - space_ship_rect.y
        fired=True

Now you can make a function which checks that beam collides with enemy objects and if True then stop blitting both the beam and that object.
Also reset the variable fired=False and reset beam position to start from spaceship again f_beam_rect=space_ship_rect

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