[Tutor] calculation issue.

[Matthew Ngaha]

thanks guys.  Eryksun your explaination was brilliant and clear. i
understood what you explained but got a bit confused with this line:

The bottom of the next pizza is at y = 100 + 100 = 200

if this Pizza (pizza.b) was on hold at position y = 100 and the
previous pizza(pizza.a) had fallen an additional 132 pixels to 232
before pizza.b was released, shouldn't pizza.b still only be at
position y = 100? how did it gain the additional 100 pixels if it was
on hold while pizza.a reached 232. i understand how you've worked it
out, just need more clarification on how the Pizza.b fell an addition
100 pixels making its total distance 200.

Sorry Alan the code was rather big, i didnt want it to be  pain for
you guys trying to help. here is the full code. I do understand the
concept and what you've explained. i just want to fully understand the
method for when i dont have a book to hold my hand:) back to the code:

# Pizza Panic
# Player must catch falling pizzas before they hit the ground

from livewires import games, color
import random

games.init(screen_width = 640, screen_height = 480, fps = 50)


class Pan(games.Sprite):
    """
    A pan controlled by player to catch falling pizzas.
    """
    image = games.load_image("pan.bmp")

    def __init__(self):
        """ Initialize Pan object and create Text object for score. """
        super(Pan, self).__init__(image = Pan.image,
                                  x = games.mouse.x,
                                  bottom = games.screen.height)

        self.score = games.Text(value = 0, size = 25, color = color.black,
                                top = 5, right = games.screen.width - 10)
        games.screen.add(self.score)

    def update(self):
        """ Move to mouse x position. """
        self.x = games.mouse.x

        if self.left < 0:
            self.left = 0

        if self.right > games.screen.width:
            self.right = games.screen.width

        self.check_catch()

    def check_catch(self):
        """ Check if catch pizzas. """
        for pizza in self.overlapping_sprites:
            self.score.value += 10
            self.score.right = games.screen.width - 10
            pizza.handle_caught()


class Pizza(games.Sprite):
    """
    A pizza which falls to the ground.
    """
    image = games.load_image("pizza.bmp")
    speed = 1

    def __init__(self, x, y = 90):
        """ Initialize a Pizza object. """
        super(Pizza, self).__init__(image = Pizza.image,
                                    x = x, y = y,
                                    dy = Pizza.speed)

    def update(self):
        """ Check if bottom edge has reached screen bottom. """
        if self.bottom > games.screen.height:
            self.end_game()
            self.destroy()

    def handle_caught(self):
        """ Destroy self if caught. """
        self.destroy()

    def end_game(self):
        """ End the game. """
        end_message = games.Message(value = "Game Over",
                                    size = 90,
                                    color = color.red,
                                    x = games.screen.width/2,
                                    y = games.screen.height/2,
                                    lifetime = 5 * games.screen.fps,
                                    after_death = games.screen.quit)
        games.screen.add(end_message)


class Chef(games.Sprite):
    """
    A chef which moves left and right, dropping pizzas.
    """
    image = games.load_image("chef.bmp")

    def __init__(self, y = 55, speed = 2, odds_change = 200):
        """ Initialize the Chef object. """
        super(Chef, self).__init__(image = Chef.image,
                                   x = games.screen.width / 2,
                                   y = y,
                                   dx = speed)

        self.odds_change = odds_change
        self.time_til_drop = 0

    def update(self):
        """ Determine if direction needs to be reversed. """
        if self.left < 0 or self.right > games.screen.width:
            self.dx = -self.dx
        elif random.randrange(self.odds_change) == 0:
           self.dx = -self.dx

        self.check_drop()


    def check_drop(self):
        """ Decrease countdown or drop pizza and reset countdown. """
        if self.time_til_drop > 0:
            self.time_til_drop -= 1
        else:
            new_pizza = Pizza(x = self.x)
            games.screen.add(new_pizza)

            # set buffer to approx 30% of pizza height, regardless of
pizza speed
            self.time_til_drop = int(new_pizza.height * 1.3 /
Pizza.speed) + 1


def main():
    """ Play the game. """
    wall_image = games.load_image("wall.jpg", transparent = False)
    games.screen.background = wall_image

    the_chef = Chef()
    games.screen.add(the_chef)

    the_pan = Pan()
    games.screen.add(the_pan)

    games.mouse.is_visible = False

    games.screen.event_grab = True
    games.screen.mainloop()

# start it up!
main()