Part 9: Progressive fruits spawning

We could tell our game is finished right now. In fact, it's already much more playable than most Python implementations with our key check between frames.

However, a cool feature could be having multiple fruits spawning over time with a higher probability when no fruit was eaten in a while.

The code is quite simple: we simply set a date to select the next time a fruit should spawn.

In fruits.h, we add our constant:

#define SNAKE_MAX_FRUIT_SPAWN_TIME 15000

In fruits.c we add the required static variable, then code to initialize it (otherwise it would be null and always trigger a new fruit at startup)

static uint64_t next_fruit_spawn = 0;

void init_fruits() {
    for (int i = 0; i < SNAKE_MAX_FRUITS ; i++) {
        FRUITS[i] = (fruit_t){UINT16_MAX, UINT16_MAX };
    }

    add_fruit();
    next_fruit_spawn = eadk_timing_millis() + (eadk_random() % SNAKE_MAX_FRUIT_SPAWN_TIME);
}

The real code is in a new function which is called at every frame: random_fruit_spawn, which will add a new fruit if necessary.

void random_fruit_spawn() {
    if (eadk_timing_millis() >= next_fruit_spawn) {
        add_fruit();
        next_fruit_spawn = eadk_timing_millis() + (eadk_random() % SNAKE_MAX_FRUIT_SPAWN_TIME);
    }
}

As usual, we add the declaration in fruits.h

void random_fruit_spawn();

Then, we call it in main.c, just after the call to move()

random_fruit_spawn();

You should commit your work on git now.

Fixing fruits collision checks

While checking this code, I realized a small bug which should be fixed (thanks to clang-tidy I use to check my code): add_fruit is calling check_fruit_collision, which does almost what we want. There are two issues with the current code:

1. check_fruit_collision remove the fruit in case of a collision, which isn't what we want when spawning a new fruit
2. check_fruit_collision also calls add_fruits (through add_fruit_if_empty), which can lead to recursive calls and possibly stack overflow

Fortunately, the fix is quite simple: just add an argument to check_fruit_collision to prevent removing fruits (and removing the call to add_fruits at the same time).

bool check_fruit_collision(snake_element_t snake_location, bool remove) {
    for (int i = 0; i < SNAKE_MAX_FRUITS ; i++) {
        if ((FRUITS[i].x == snake_location.x) && (FRUITS[i].y == snake_location.y)) {
            if (remove) {
                FRUITS[i] = (fruit_t){UINT16_MAX, UINT16_MAX};
                add_fruit_if_empty();
            }

            return true;
        }
    }

    return false;
}

We update the corresponding signature in the header file:

bool check_fruit_collision(snake_element_t snake_location, bool remove);

The call in main.c:

if (check_fruit_collision(snake_location, true)) {

And finally the call in fruits.c:

if (check_fruit_collision((snake_element_t){x, y}, false)) {

This doesn't fix the warning given by clang-tidy (which would probably be fixed by duplicating the function instead of using a parameter), but this should fix our bug.

This is a great example of how can small sneaky errors in C go undetected for a while, so I decided to keep track of it in this tutorial

As always after a bug fix, create a new git commit to save your edits

I hope next time we won't have to do bugfixing again, as we will work on score calculation, with best score saving.