Question about snake game

[Marcus]

Here's a port of an n6 example game. Hopefully you can find some clues by looking at the code   I don't remember why I implemented the game like this, and probably there are smarter ways.

Code:

' Port of n6 example game.

SNAKE_MAX_LENGTH = 30*40
UP = 1
DOWN = 2
LEFT = 3
RIGHT = 4
snake = dim(SNAKE_MAX_LENGTH, 2)
level = dim(40, 30)

set window "Smape", 320, 240, false, 2
set redraw off

do
    snakeLength = 1
    snakeHead = 0
    snakeDirection = 0
    speed = 10
    speedCounter = speed
    snake[snakeHead][0] = 20
    snake[snakeHead][1] = 15
    for y = 0 to 29  for x = 0 to 39  level[x][y] = 0
    gameOver = false
    nextPlupTime = clock()
    do
        if clock() >= nextPlupTime
            if rnd(3) = 0  level[rnd(40)][rnd(30)] = 2
            else  level[rnd(40)][rnd(30)] = 1
            nextPlupTime = clock() + 2000 + rnd(2000)
        endif

        if keydown(38) and snakeDirection <> DOWN  snakeDirection = UP
        if keydown(40) and snakeDirection <> UP  snakeDirection = DOWN
        if keydown(37) and snakeDirection <> RIGHT  snakeDirection = LEFT
        if keydown(39) and snakeDirection <> LEFT  snakeDirection = RIGHT
   
        speedCounter = speedCounter - 1
        if speedCounter = 0
            prev = snakeHead
            if snakeDirection > 0  snakeHead = (snakeHead + 1)%SNAKE_MAX_LENGTH
            speedCounter = speed
            if snakeDirection = UP
                snake[snakeHead][0] = snake[prev][0]
                snake[snakeHead][1] = snake[prev][1] - 1
            elseif snakeDirection = DOWN
                snake[snakeHead][0] = snake[prev][0]
                snake[snakeHead][1] = snake[prev][1] + 1
            elseif snakeDirection = LEFT
                snake[snakeHead][0] = snake[prev][0] - 1
                snake[snakeHead][1] = snake[prev][1]
            elseif snakeDirection = RIGHT
                snake[snakeHead][0] = snake[prev][0] + 1
                snake[snakeHead][1] = snake[prev][1]
            endif
            x = snake[snakeHead][0]
            y = snake[snakeHead][1]
            if x < 0 or x >= 40 or y < 0 or y >= 30
                gameOver = true
            else
                if level[x][y] > 0
                    snakeLength = snakeLength + 1
                    if level[x][y] = 2  speed = max(speed - 1, 0)
                    level[x][y] = 0
                endif
            endif
        endif

        set color 0, 0, 0
        cls

        for y = 0 to 29
            for x = 0 to 39
                if level[x][y] = 1
                    set color 0, 255, 0
                    draw rect x*8, y*8, 8, 8 , true
                elseif level[x][y] = 2
                    set color 255, 0, 0
                    draw rect x*8, y*8, 8, 8, true
                endif
            next
        next

        set color 255, 255, 255
        set caret 0, 0
        x = snake[snakeHead][0]
        y = snake[snakeHead][1]
        for i = snakeHead to snakeHead - snakeLength + 1
            j = i
            if j < 0 then j = j + SNAKE_MAX_LENGTH
            draw rect snake[j][0]*8, snake[j][1]*8, 8, 8, true
            if i <> snakeHead
                if snake[j][0] = x and snake[j][1] = y then gameOver = true
            endif
        next

        wait 10
        redraw
    until gameOver
loop

I'll see if I can understand the code where the body follows the head, thank you.

I barely looked at the code. But I believe the snake "moves" through the 'snake' array. Every element in the array contains a position (x and y value). The snake's head is a moving index in the array. Every time the snake moves one step, the head index increases and a new position is added to the array. That way, the tail is always present as earlier indexes in the array. So if the length of the snake is 4, the positions drawn are those at snake[snakeHead], snake[snakeHead - 1] .. snake[snakeHead - 3].

Edit: The % operator is used to keep the indexes within the array size. When the snake head index reaches the end of the array it starts over at 0. The length of the array is exactly enough for the snake to cover the entire screen

You can probably write smarter code that just stores the turns that the snake does or something. But that would require more complicated code ... I think