execute_flat

[bus693]

I'm new to evolved and ecs, thanks for making this library!

I'm working on a naive implementation of AABB collision.

local es = <all entities that have FRAGMENTS.POSITION>
for _, e1 in ipairs(es) do
  for _, e2 in ipairs(es) do
    if e1 ~= e2 then
      -- check for and handle collision
    end
  end
end

When using the builder pattern, the callback within :execute() only has access to the individual chunk, so we need a helper function to aggregate the entities across different chunks.

Would it make sense to include something like :execute_flat(callback) where the callback receives a list of all the entities, so that we can write something like this?

evolved
	.builder()
	:name("SYSTEM.COLLISION")
	:include(FRAGMENTS.POSITION)
	:execute_flat(function(chunk_list, entities, entity_count, dt)
          -- the nested for loops
	end)
	:build()

[BlackMATov]

Hello! Thanks for your interest in the library and for your question :-)

So, the library doesn't provide a built-in way to access all matching chunks, but you can implement your own helper function to aggregate them and iterate over them in the system epilogue. Or, just use a separate query and iterate over the results in your system prologue or epilogue.

I will think about adding something like :execute_flat, but I doubt it will be added to the core library.

My recommendation is to use a separate query. With it, you can iterate over all matching entities in your system however you like. Something like this:

-- collision_system.lua

local evolved = require 'evolved'

local PHYSICAL_BODY_QUERY = evolved.builder()
  :include(FRAGMENTS.POSITION)
  :build()

evolved.builder()
  :name("SYSTEM.COLLISION")
  :prologue(function()
    for a_chunk, a_entity_list, a_entity_count in evolved.execute(PHYSICAL_BODY_QUERY) do
      for b_chunk, b_entity_list, b_entity_count in evolved.execute(PHYSICAL_BODY_QUERY) do
      end
    end
  end)
  :build()

But don't forget that epilogues and prologues are not called in the deferred scope. So, if you want to modify the entities (I mean making structural changes) in this system, you will need to defer the modifications with evolved.defer() and evolved.commit().