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For my shmup project (bullet hell/danmaku), my first step was to work on the bullet/pattern system because it's related to the core of the gameplay (dodging bullets); and also because it's accountable to the beauty of the game.

First, I need limits. I decide to handle 128 bullets at a time. New bullets will replace the old one. From my perspective, is not a big deal. Players probably won't notice it. But if it happens, maybe it's because that bullet stays visible too long on the screen, turning arround following a circular path or simply moving too slowly. So, fuck that bullet.

I decide to create a table of bullet objects during the _init() proccess and reuse them instead of creating/deleting every time. It is called object pool

The process: every time I need to shoot a bullet, I select the next bullet object in the pool, If I reach the last one, I loop to the first. Simple.

To do that, I need:

  • a list of bullet objects,
  • an index for the next bullet index to use
  • and a number of max bullet:
bullets={}
bullets.next=1
bullets.len=128

Notice how the bullets table is used as an indexed list (to store bullets objects) and an object (to store properties).

During the _init() process, I warm up the table by creating all the bullet objects:

for i=1,bullets.len do
  local b={}
  bullets[i]=b
  ...later... -- warmup bullet properties
end

Next, every time I want to shoot a new bullet:

function shoot(...later...)
  -- get the bullet object
  local b=bullets[bullets.next]
  -- increment the next property
  bullets.next=(bullets.next%bullets.len)+1
  ...later... -- setup bullet properties
end

This little code make the .next property goes from 1 to 128 and loop to 1. Remember, tables in lua do not start at 0, but 1.

To draw the bullets:

for i=1,bullets.len do
 local b=bullets[i]
 spr(...later...)
end

I'm using a simple for loop here and not a for all() because I need the index for other purpose.

I'm using this technique for every data objects in my shmup game: bullet pattern functions, enemy ship, particles
With a little subtlety for the particles, because the objects are render sequentially, particles would appear stacked on each other. To fix that, when I need to create a new one, I do not increment by 1 but 7:

particles.next=(particles.next+6)%32+1

That's all for today, I hope you will use object pooling like crazy for your futur pico8 projects.

technique
P#32758 2016-11-25 16:29


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