Playing Sounds

Now let's add sound effects and music to our game.

All audio assets used in this tutorial are CC0 and were obtained from
freesound.

---

Health Loss Sound

This sound will play when a meteor reaches the end of the screen.

Update the behaviour behaviours/meteor.lua:

return {
    init = function(state)
        sucata.scene.add_tag(state, "meteor")

        state.speed = state.speed or math.random(100, 200)
        state.health = state.health or math.random(1, 5)
        state.force_y = state.speed
    end,

    tick = function(state)
        if state.y > 540 then
            sucata.events.emit("meteor_reached", state)

            sucata.audio.play({
                sound = "src://sounds/lose.ogg"
            })

            sucata.scene.destroy(state)
        end

        state.atlas_x = state.health - 1
    end
}

Note src:// represents the root directory of the project. Use this prefix whenever referencing files inside the project.

---

Shooting Sound

This sound will play when the player fires a bullet.

Update behaviours/bullet.lua:

return {
    init = function(state)
        state.speed = state.speed or 400
        state.force_y = -state.speed

        -- Play shooting sound when the bullet is spawned
        sucata.audio.play({
            sound = "src://sounds/shoot.ogg"
        })
    end,
    ...
}

---

Meteor Hit Sound

Now we will add a sound effect when a meteor is hit by a bullet.

Update behaviours/bullet.lua:

return {
    tick = function(state)
        local meteors = sucata.scene.get_entities_by_tag("meteor")

        for _, id in ipairs(meteors) do
            local meteor = sucata.scene.find_by_id(id)

            if meteor and sucata.math.overlapping({
                x = state.x - 8,
                y = state.y - 8,
                width = 16,
                height = 16
            }, {
                x = meteor.x - 16,
                y = meteor.y - 16,
                width = 32,
                height = 32
            }) then
                health.remove(meteor)

                if meteor.health <= 0 then
                    sucata.events.emit("meteor_destroyed", meteor)
                    sucata.scene.destroy(meteor)
                end

                -- Play shooting sound when the meteor is hitted
                sucata.audio.play({
                    sound = "src://sounds/explosion.ogg"
                })

                sucata.scene.destroy(state)
                break
            end
        end
    end
}

---

Playing Music

Now we will add background music to the game.

Create a new behaviour behaviours/music.lua:

return {
    init = function(state)
        if state.music then
            state.music_id = sucata.audio.play({
                sound = state.music,
                loop = true,
                volume = 0.5
            })
        end
    end
}

Register the behaviour in behaviours/init.lua:

```lua id="e5vwy2" return { ... Music = require("behaviours.music"), }

Now create an entity responsible for playing the background music.

Create `entities/music.lua`:

```lua id="h53grq"
local function music()
    return {
        state = {
            music = "src://sounds/music.ogg"
        },

        behaviours = {
            Behaviours.Music
        }
    }
end

return music

Finally, spawn the music entity in main.lua:

local music = require("entities.music")

sucata.scene.spawn(music())

The background music will now play in a loop while the game is running.