Creating Meteors

Now we will create the enemies of the game: meteors that fall from the sky.

Creating the Meteor Behaviour

First, we will create a behaviour responsible for making meteors fall.

Create the file behaviours/apply_forces.lua, that will make the meteor move:

return {
    init = function (state)
        state.x = state.x or 0
        state.y = state.y or 0
        state.force_x = state.force_x or 0
        state.force_y = state.force_y or 0
    end,
    tick = function (state) 
        local dt = sucata.time.get_delta()
        state.x = state.x + (state.force_x * dt) -- Move x by force_x in the state
        state.y = state.y + (state.force_y * dt) -- Move y by force_y in the state
    end
}

Create the file behaviours/meteor.lua:

return {
    init = function(state)
        sucata.scene.add_tag(state, "meteor") -- Add the "meteor" tag to the entity
        state.speed = state.speed or math.random(100, 200) -- Random fall speed
        state.health = state.health or math.random(1, 5) -- Random meteor health
        state.force_y = state.speed -- define force to move
    end,

    tick = function(state)
        if state.y > 540 then -- When the meteor leaves the screen
            sucata.events.emit("meteor_reached", state) -- Emit an event
            sucata.scene.destroy(state) -- Destroy the meteor
        end
    end
}

Register the behaviour in behaviours/init.lua:

return {
    ...
    ApplyForces = require("behaviours.apply_forces"),
    Meteor = require("behaviours.meteor"),
}

---

Creating the Meteor Entity

Now we will create the meteor entity.

Create the file entities/meteor.lua:

local function meteor(x, y)
    return {
        state = {
            x = x, -- Meteor position
            y = y
        },

        behaviours = {
            Behaviours.Meteor, -- Meteor logic
            Behaviours.ApplyForces, -- Apply forces logic
            Behaviours.DrawSprite -- Render the meteor
        }
    }
end

return meteor

Spawn a meteor in main.lua:

local Meteor = require("entities.meteor")

sucata.scene.spawn(Meteor(300, 100))

The game should now look like this:

---

Creating a Random Start Position Behaviour

Now we will create a behaviour that spawns entities at a random position.

Create the file behaviours/random_start_position.lua:

return {
    init = function(state)
        state.x = state.x or math.random(16, 960 - 16) -- Random X within screen bounds
        state.y = state.y or math.random(16, 540 - 16) -- Random Y within screen bounds
    end
}

Register the behaviour in behaviours/init.lua:

return {
    ...
    RandomStartPosition = require("behaviours.random_start_position")
}

---

Spawning Meteors at Random Positions

Now we will update the meteor entity so it spawns at a random X position.

Update entities/meteor.lua:

local function meteor()
    return {
        state = {
            y = -16 -- Start slightly above the screen
        },

        behaviours = {
            Behaviours.RandomStartPosition, -- Random spawn position
            Behaviours.Meteor, -- Meteor logic
            Behaviours.ApplyForces, -- Apply forces logic
            Behaviours.DrawSprite -- Render the meteor
        }
    }
end

return meteor

Now meteors will spawn with a random X position and fall from the top of the screen.