having trouble iterating through a loop and drawing boxes

Question

I'm trying to implement Tetris in Pygame. I wanted to test out an algorithm involving arrays that would in theory draw boxes in a grid. Instead, whenever I run the code, the window pops up and only one square is drawn in the corner of the window.

So I started by making a 2d array -- 20 arrays each with 10 zeros, each zero representing a cell in the game board. Then i used a for loop to iterate through each cell, theoretically drawing a square for each zero in the array. I'm still at the stage where I'm trying to iterate through each zero in a sub-array.

game.py:

    import pygame

    board_arr = [[0,0,0,0,0,0,0,0,0,0],
                 [0,0,0,0,0,0,0,0,0,0],
                 [0,0,0,0,0,0,0,0,0,0],
                 [0,0,0,0,0,0,0,0,0,0],
                 [0,0,0,0,0,0,0,0,0,0],
                 [0,0,0,0,0,0,0,0,0,0],
                 [0,0,0,0,0,0,0,0,0,0],
                 [0,0,0,0,0,0,0,0,0,0],
                 [0,0,0,0,0,0,0,0,0,0],
                 [0,0,0,0,0,0,0,0,0,0],
                 [0,0,0,0,0,0,0,0,0,0],
                 [0,0,0,0,0,0,0,0,0,0],
                 [0,0,0,0,0,0,0,0,0,0],
                 [0,0,0,0,0,0,0,0,0,0],
                 [0,0,0,0,0,0,0,0,0,0],
                 [0,0,0,0,0,0,0,0,0,0],
                 [0,0,0,0,0,0,0,0,0,0],
                 [0,0,0,0,0,0,0,0,0,0],
                 [0,0,0,0,0,0,0,0,0,0],
                 [0,0,0,0,0,0,0,0,0,0]]

    def iterate_board(screen, rect):
        for i in board_arr:
            for j in i:
                pygame.draw.rect(screen, "red", rect)
                rect.x += rect.width

and then I call the "iterate_board" function inside of main.py.

The problem with this is that only one square seems to get drawn.

    import pygame
    import game

    pygame.init()
    screen = pygame.display.set_mode((600,600))
    #screen = game.screen
    bg_hue = "black"
    run = True
    clock = pygame.time.Clock()

    squ = pygame.Rect(0, 10, 20, 20)

    while run:
        for event in pygame.event.get():
            if event.type == pygame.QUIT:
                run = False
            
        screen.fill(bg_hue)

        game.iterate_board(screen,squ)

        pygame.display.update()
     
        clock.tick(60)

    pygame.quit()

EDIT: By request, here's the rest of the code. I tweaked it a little, but it's still generally the same

Answer 1

You paint all the blocks in one row because you never change rect.y. Then, in the next run of the while loop, you overwrite everything with screen.fill(bg_hue) and try to paint again, but the position of rect.x is now on the right outside the window area. This means that you actually paint, but no one can see it anymore.

I added the change to the y-position, the reset of the x-position for a new row, and made sure to not overwrite the initial square.

I also added a function to alter random blocks of the board, so that you can see that it works.

import random
import pygame

the_board = [[0 for x in range(10)] for y in range(20)]


def change_random_block(board):
    x = random.randrange(len(board))
    y = random.randrange(len(board[x]))
    board[x][y] = 1 - board[x][y]


def iterate_board(screen, initial_rect, board):
    rect = initial_rect.copy()
    for row in board:
        for block in row:
            if block == 0:
                pygame.draw.rect(screen, "red", rect)
            rect.x += rect.width
        rect.x = initial_rect.x
        rect.y += rect.height


pygame.init()
screen = pygame.display.set_mode((600, 600))
bg_hue = "black"
run = True
clock = pygame.time.Clock()
square = pygame.Rect(0, 10, 20, 20)

while run:
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            run = False

    screen.fill(bg_hue)
    iterate_board(screen, square, the_board)
    pygame.display.update()
    clock.tick(60)
    change_random_block(the_board)

pygame.quit()

---

A small hint: If you use rect.x += rect.width + 1 and rect.y += rect.height + 1 you can see the grid.