Groups

"Groups" are what contains entities.
To get a group, use umg.group:

local drawGroup = umg.group("x", "y", "image")

Groups are automatically populated with entities.
This one takes entities with x, y, and image components.¹

We can also do other stuff:

drawGroup:onAdded(function(ent)
    print("entity added to drawGroup! :) ")
end)

drawGroup:onRemoved(function(ent)
    print("aww, entity removed from drawGroup")
    -- happens when an entity is deleted, or when components are removed
end)


local function draw()
    -- iteration is the same as a regular lua table:
    for i, ent in ipairs(drawGroup) do
        ...
    end
end


drawGroup:len() -- gets length of a group

drawGroup:has(ent) -- returns true if `ent` is in drawGroup, false otherwise.

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1. doesn't matter if the components are shared or regular, as long as the entity has all of them.↩