Pygame moving an image in a direction

Question

This is my first post here and I would really appreciate it if someone could tell me how to move an image to a point. Here's my code:

class bullet:

image = "bullet.png"
spr = pygame.image.load(image).convert_alpha()
x = 0
y = 0
def __init__(self, a, b):
    self.x = a
    self.y = b

    while self.x > 0 and self.x < 500 and self.y > 0 and self.y < 500:#the boundries for the bullet
    CODE GOES IN HERE TO MOVE IMAGE

Answer 1

Take a look at this example:

import pygame
import base64
import math
import random

# some functions for vector math

def magnitude(v):
    return math.sqrt(sum(v[i]*v[i] for i in range(len(v))))

def add(u, v):
    return [(a+b) for (a, b) in zip(u, v)]

def sub(u, v):
    return [(a-b) for (a, b) in zip(u, v)]

def dot(u, v):
    return sum((a*b) for a, b in zip(u, v))

def normalize(v):
    vmag = magnitude(v)
    return [ v[i]/vmag  for i in range(len(v)) ]

def length(v):
  return math.sqrt(dot(v, v))

def angle(v1, v2):
  return math.acos(dot(v1, v2) / (length(v1) * length(v2)))

def get_image():
    dec = base64.b64decode(img, 'UTF-8')
    surf = pygame.image.fromstring(dec, (32, 32), 'RGBA')
    return surf

def rot_center(image, angle):
    orig_rect = image.get_rect()
    rot_image = pygame.transform.rotate(image, angle)
    rot_rect = orig_rect.copy()
    rot_rect.center = rot_image.get_rect().center
    rot_image = rot_image.subsurface(rot_rect).copy()
    return rot_image

class Actor(object):

    surf = None

    def __init__(self):
        self.x, self.y = (0, 0)
        self.speed, self.angle = 1.7, 0
        self.target_vector = [0, 0]

    @property
    def img(self):
        if not self.surf:
            self.surf = get_image()
        return self.surf


    @property
    def pos(self):
        return self.x, self.y

    @property
    def int_pos(self):
        return map(int, self.pos)

    @property
    def center_pos(self):
        return [a-16 for a in self.int_pos]

    def update(self):
        if self.speed == 0:
            return

        # apply speed to target_vector
        move_vector = [c * self.speed for c in normalize(self.target_vector)]

        # update position by adding the position vector to the movment vector
        self.x, self.y = add(self.pos, move_vector)

    def draw(self, s):
        s.blit(rot_center(self.img, self.angle), self.center_pos)

def fire(start, angle, target_vector):
    act = Actor()
    act.x, act.y = start
    act.angle = angle
    act.target_vector = target_vector
    return act

def main():    
    pygame.init()
    quit = False
    s = pygame.display.set_mode((300, 300))
    c = pygame.time.Clock()
    pos = (134, 268)
    actors = []
    FIRE = pygame.USEREVENT + 1
    pygame.time.set_timer(FIRE, 1000)
    while not quit:

        quit = pygame.event.get(pygame.QUIT)

        if pygame.event.get(FIRE):
            angle = random.randint(0, 180)
            print 'angle is ', angle
            # calculate vector that represents the direction
            rangle = math.radians(-angle)
            target_vector = normalize((math.cos(rangle), math.sin(rangle)))
            actors.append(fire(pos, angle, target_vector))

        pygame.event.poll()
        for ar in actors:
            ar.update()
        s.fill((255, 255, 255))
        for ar in actors:
            ar.draw(s)
        pygame.display.flip()
        c.tick(60)

img = 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AAAAAAAAAAAAAAAAAAAAAAAAAAAAAUAAAAP8AAADTAAAAVAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAABRAAAATgAAAF4AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAD4AAAA7AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA=='

if __name__ == '__main__':
    main()

Here, a random angle is converted to a vector which is used to move an object.

Answer 2

First of all you need a screen to set up the display:

size = (640, 480) # window size
screen = pygame.display.set_mode(size) # screen where the image will be displayed

You need to use the screen.blit to display the image. It takes the image object and x,y coordinates as parameters. In your case it should be like:

screen.blit(spr, (x,y)) # draws image at x,y coordinate