Coordinates of a Pygame image

Question

How can I get the x and y coordinates of an image in Pygame? I need this for a game where I have to get the shot out right below an enemy. This is the code:

# -*- coding: cp1252 -*-
import sys
import random
import pygame
print pygame.init()  #inicia todo o módulo pygame (pygame.init() retorna algo, não faz a inicialização completa por isso so print
x_player, y_player = 650, 440
screen = pygame.display.set_mode((700, 500))  # screen's size width and height
pygame.display.set_caption("Space Invaders v1.0.0")  # name of the screen
pygame.display.flip()
invaders = pygame.image.load(
    "C:\\Users\\bernardo\\Documents\\IFC\\Programação\\SpaceInvaders-my_own\\space-invaders.jpeg").convert()
player = pygame.image.load(
    "C:\\Users\\bernardo\\Documents\\IFC\\Programação\\SpaceInvaders-my_own\\28006.png").convert()  # loads the image
    #  of the player and put it on a variable
mother_ship = pygame.image.load(
    "C:\\Users\\bernardo\\Documents\\IFC\\Programação\\SpaceInvaders-my_own\\mother_ship.png").convert()
lifes = pygame.image.load(
    "C:\\Users\\bernardo\\Documents\\IFC\\Programação\\SpaceInvaders-my_own\\28007.png").convert()
shots = pygame.image.load(
    "C:\\Users\\bernardo\\Documents\\IFC\\Programação\\SpaceInvaders-my_own\\shots_and_bombs2.png").convert()
pygame.font.init()
clock = pygame.time.Clock()
player_size = player.get_size()
move_x = 0

x_invaders, y_invaders = 60, 60
lifes_list = [lifes, lifes, lifes]
x_mother = 0
invaders_matrix = [[invaders] * 11] * 5
existe_nave = False
start = True
while len(lifes_list) != 0:
screen.fill([0, 0, 0]) # color of the screen (rgb)
screen.blit(player, [(x_player / 2), y_player]) # initial position of player
clock.tick(35) # are going to happen just movements on 23 frames per second
screen.blit(shots, (invaders_matrix[random.randint(0, 4)][random.randint(0, 10)].get_rect().centerx,
        invaders_matrix[random.randint(0, 4)][random.randint(0, 10)].get_rect().centery))

x_invaders, y_invaders = 105, 125
for invader in range(len(invaders_matrix)):
    for invad in range(len(invaders_matrix[invader])):
        screen.blit(invaders_matrix[invader][invad], [x_invaders, y_invaders])
        x_invaders += 45
    x_invaders = 105
    y_invaders += 30

if existe_nave and (x_mother < 700):
    screen.blit(mother_ship, [x_mother, 35])
    x_mother += 4.5
    screen.blit(mother_ship, [x_mother, 35])

elif random.randint(0, 800) == 0:
    existe_nave = True
    x_mother = 0

width_for_lifes = 680
for icon_lifes in lifes_list:
    width_for_lifes -= 50
    screen.blit(icon_lifes, (width_for_lifes, 15))

for event in pygame.event.get():
    if event.type == pygame.QUIT:
        pygame.quit()
        sys.exit()
        start = False
    if event.type == pygame.KEYDOWN:
        if event.key == pygame.K_LEFT:
            move_x -= 10
            start = False
        if event.key == pygame.K_RIGHT:
            move_x += 10
            start = False
    if event.type == pygame.KEYUP:
        if event.key == pygame.K_LEFT or event.key == pygame.K_RIGHT:
            move_x = 0
            start = False

if x_player >= 1280:
    x_player = 1280
if x_player <= 25:
    x_player = 25

font = pygame.font.Font(None, 36)
text = font.render("Lifes", 1, (0, 255, 85))
screen.blit(text, (450, 15))

font = pygame.font.Font(None, 36)
text = font.render("Score", 1, (0, 255, 85))
screen.blit(text, (20, 15))

x_player += move_x

pygame.display.update()

Answer 1

After you place an image in the main image (screen) using a call to the "blit" method as this code does, the image becomes part of the main image:

Blit is like stamping a piece of paper: what you know is where you had the stamp stamped - if you move the place stamp, just using your eyes to "see" where the image is. But when we program games in this style, "see" is an expensive operation - in this case, almost impossible. (it is possible, but you would have to use image recognition and a series of programming techniques almost a hundred times more sophisticated than the game itself)

To know where each invader ship is and place the shot there, you must store the coordinates of each ship in data structures in memory -

In your case, the lines

     x_invaders += 45
x_invaders = 105
y_invaders += 30

position the aliens in a "handmade" way - and the data on each alien are discarded and recalculated in real time in the next frame.

This was a necessary technique in video games with a few KB of memory where this type of game was first created. Nowadays, what is worth it is you create an object in memory for each invader ship (and other elements in play), and associate the data of each element to itself. So any alien in the matrix will have information of where he is.

Pygame provides a very cool class, which has interaction with the classes of Group of the game, to serve as a basis for its objects: the class pygame.Sprite .

When you your enemies derived from pygame. Sprite, for example, usually they will have an object pygame.Rect associated - which contains all enemy coordinates, at each moment (your program that updates these coordinates). But in doing so, you can have the center coordinate horizontally, on the underside of each invader simply by doing:

x, y = invader.rect.centerx, invader.rect.bottom

Feel free to write to me privately if you want more guidance on this game - I am working on a similar project with my students. (my contact is in the profile)