0
\$\begingroup\$

I only know C, no other language.

How do I use a linked list to store projectiles in sdl2?

My bullet currently has an sdl_image, has been queried and has the following properties:

//Bullet is visible
.plasma_rect[0].x = 0,
.plasma_rect[0].y = 0,
.plasma_rect[0].h = 50,
.plasma_rect[0].w = 50,

//Bullet is not visible
.plasma_rect[1].x = 0,
.plasma_rect[1].y = 100,
.plasma_rect[1].h = 50,
.plasma_rect[1].w = 50,

//Player x&y velocity, xvol *3 of player is used as speed of bullet
.player_xvol = 5,
.player_yvol = 5,

How the bullet shoots in the main loop:

  update_sprite(&game);
  directionbullet(&game);
  SDL_RenderClear(game.renderer);
  SDL_RenderCopy(game.renderer, game.background_image, NULL, NULL);
  SDL_RenderCopyEx(game.renderer, game.player_image, NULL, &game.player_rect, angle, NULL, SDL_FLIP_NONE);

 //int i is set globally as 1 initially, but changes to 0 when spacebar is pressed

 
    if(i == 1) {
  SDL_RenderCopyEx(game.renderer, game.plasma_image, &game.plasma_rect[i], &game.bullet_dist, angle - 90, NULL, SDL_FLIP_NONE);
   }

    if(i == 0) { 
      if(count == 0) {
      game.plasma_rect[i].x = game.player_rect.x;
      game.plasma_rect[i].y = game.player_rect.y;
      weapons_handling(&game);

//angle is calculated in "update_sprite" function, bullet angle is calculated only once here right before it shoots, so that the bullet texture will be facing the direction of the sprite.

      bulangle = angle - 90;
        count++;
      }
   
  SDL_RenderCopyEx(game.renderer, game.plasma_image, NULL, &game.plasma_rect[i], bulangle, NULL, SDL_FLIP_NONE);
 if(check(&game)) {
      i = 1;
      count = 0;

//calculated in "directionbullet" function

      Vx = 0;
      Vy = 0;
    }
  } 

  SDL_RenderPresent(game.renderer);
  SDL_Delay(16);

However, doing this only allows me to fire one bullet, wait until the bullet sprite exits view of the screen, then fire again. How do I use a linked list or some other data structure to achieve multiple projectiles firing based on the amount of times I click spacebar without having to wait. I am very new to this, I might not even be asking the right questions, please bare with me.

\$\endgroup\$
0

2 Answers 2

Reset to default
1
\$\begingroup\$

You can have a plain array of bullets that you iterate over every frame to advance them until they need to vanish.

Then each time you need to shoot you pick an empty slot and initialize a bullet in there.

Every time a bullet reaches end of life (when they hit something or go offscreen) then you set that slot to dead.

The simplest way to achieve both of these is using a alive count to easily find a free slot and when a bullet dies you swap it with the last one and decrement the alive count:

// in your Game struct
int aliveBullets;
Bullet* bullets;

The Bullet struct then has all the data that makes each bullet unique, like the angle, its position, its speed, etc.

Bullet* AllocBullet(Game* game){
    if(game->aliveBullets >= BULLET_MAX)return null;
    Bullet* result = game->bullets[game->aliveBullets++];
    result->alive = true;
    return result;
}

void DeallocBullet(Game* game, int bulletIndex){
    if(bulletIndex < game->aliveBullets)
        memcpy(game->bullets[bulletIndex], game->bullets[game->aliveBullets], sizeof(Bullet));
    game->bullets[game->aliveBullets].alive = false;
    game->aliveBullets--;
}

Then to render you iterate over the bullets array and render each of them.

for(int i = 0; i < game->aliveBullets; i++){
    Bullet* bullet = game->bullets[i];
    //render bullet
}

Similarly you will also need to iterate over each of them to update their position and do the collision logic per bullet.

\$\endgroup\$
7
  • \$\begingroup\$ If you store the bullet data structure itself in the array, rather than just a pointer, then this approach has better data locality than a linked list, and can give substantial performance wins when you have a lot of entities you're iterating and updating/drawing each frame. \$\endgroup\$ Commented May 5 at 11:37
  • \$\begingroup\$ Thank you so much. \$\endgroup\$ Commented May 5 at 13:19
  • \$\begingroup\$ Also, i'm assuming I would just iterate over the bullets array until I reach a null to render them? And how should I go about updating each bullet position, assuming I already have a function that does the necessary calculations. \$\endgroup\$ Commented May 5 at 13:53
  • \$\begingroup\$ This is not a linked list, it's a array. With a straight for(int i = 0; i < game->aliveBullets; i++) you will get through all the alive bullets. \$\endgroup\$ Commented May 5 at 13:57
  • \$\begingroup\$ Okay, and there wont be any conflicts with them sharing the same sdl texture? \$\endgroup\$ Commented May 5 at 14:05
0
\$\begingroup\$

Take a look at https://www.parallelrealities.co.uk/tutorials/shooter/shooter5.php. You'll see there is an C struct called Entity that has a next property. Then look at the fireBullet() function where you will see a bullet Entity being created. Lastly, you'll see a function called doBullets() which loops through the linked list of bullets and moves each of them dx and dy units. You can try to get this example working, and once you fully understand how it works, you should be able to implement your own linked list of bullets and not have to wait for the bullet to exit the screen before firing another one.

\$\endgroup\$
0

You must log in to answer this question.

Start asking to get answers

Find the answer to your question by asking.

Ask question

Explore related questions

See similar questions with these tags.