move_off_screen.py

import sys
import math
import pygame as pg


class Block(pg.sprite.Sprite):
    def __init__(self, pos, speed, next_move):
        super(Block, self).__init__()
        self.image = pg.Surface((50,50)).convert()
        self.image.fill(pg.Color("red"))
        self.rect = self.image.get_rect(center=pos)
        self.exact_position = list(self.rect.center)
        self.speed = speed #Pixels per second
        self.target = None
        self.vec = None
        self.distance = None
        self.next_move = next_move

    def update(self, dt):
        if self.target:
            travelled = math.hypot(self.vec[0]*dt, self.vec[1]*dt)
            self.distance -= travelled
            if self.distance <= 0:
                self.rect.center = self.exact_position = self.target
                self.target = None
                if self.next_move:
                    target = (550, self.next_move.rect.centery)
                    self.next_move.get_new_instruction(target)
            else:
                self.exact_position[0] += self.vec[0]*dt
                self.exact_position[1] += self.vec[1]*dt
                self.rect.center = self.exact_position

    def draw(self, surface):
        surface.blit(self.image, self.rect)

    def get_new_instruction(self, target):
        x = target[0]-self.exact_position[0]
        y = target[1]-self.exact_position[1]
        self.distance = math.hypot(x, y)
        try:
            self.vec = self.speed*x/self.distance, self.speed*y/self.distance
            self.target = list(target)
        except ZeroDivisionError:
            pass
        

class Control(object):
    def __init__(self):
        pg.init()
        pg.display.set_caption("Move To Target")
        self.screen = pg.display.set_mode((500,500))
        self.screen_rect = self.screen.get_rect()
        self.clock = pg.time.Clock()
        self.fps = 60.0
        self.done = False
        previous = None
        blocks = []
        for i in range(4):
            pos = self.screen_rect.centerx, self.screen_rect.bottom-100-i*100
            previous = Block(pos, 500, previous)
            blocks.append(previous)
        self.click_block = blocks[-1]
        self.blocks = pg.sprite.Group(blocks)

    def event_loop(self):
        for event in pg.event.get():
            if event.type == pg.QUIT:
                self.done = True
            elif event.type == pg.MOUSEBUTTONDOWN:
                if event.button == 1:
                    if self.click_block.rect.collidepoint(event.pos):
                        target = 550, self.click_block.rect.centery
                        self.click_block.get_new_instruction(target)

    def update(self, dt):
        self.blocks.update(dt)

    def draw(self):
        self.screen.fill((30,40,50))
        self.blocks.draw(self.screen)

    def main_loop(self):
        while not self.done:
            dt = self.clock.tick(self.fps)/1000.0
            self.event_loop()
            self.update(dt)
            self.draw()
            pg.display.update()


def main():
    app = Control()
    app.main_loop()
    pg.quit()
    sys.exit()


if __name__ == "__main__":
    main()