Introduction to Scion 2D

Scion 2D is a simple 2D game engine written in C++ that I am creating for my YouTube channel for educational purposes and to become a better programmer. There is still lots of work to do; however, we are making some headway.

Technologies

• OpenGL 4.5.
• Sol3 - for Lua bindings.
• Lua 5.3 - Scripting Language.
• SOIL - for texture loading.
• ENTT - for the ECS (Entity Component System).
• SDL2 - for all windowing/input devices/ and much more.
• SDL Mixer - for music and soundFX.
• Box2D - for all the Physics
• ImGui - TODO: Imgui is in the future when we create the actual editor.

About

Asset Manager

The Asset Manager is what is used to store the games textures, fonts, music, soundFx, and shaders. Before the assets can be used in the game, they must be added into the asset manager successfully.

• Functions
  • add_texture
  • add_music
  • add_soundfx
  • add_font

Functions:

add_texture

Example:

-- Add the hero texture to the asset manager
if AssetManager.add_texture("hero", "./assets/textures/hero.png", true) then 
	print("Added texture [hero] successfully")
else
	print("Failed to add the [hero] texture.")
end

-- Consider adding all the textures and their paths to a table and looping.

add_music

Example:

-- Add the title music to the asset manager
if AssetManager.add_music("title", "./assets/music/title.mp3") then 
	print("Added music [title] to Asset Manager successfully")
else
	print("Failed to add the [title] music to the Asset Manager.")
end

add_soundfx

Example:

-- Add the sword SoundFx to the asset manager
if AssetManager.add_soundfx("sword", "./assets/soundfx/sword.wav") then 
	print("Added soundFx [sword] to Asset Manager successfully")
else
	print("Failed to add the [sword] soundFx to the Asset Manager.")
end

add_font

Example:

-- Add the Pixel font to the asset manager
if AssetManager.add_font("pixel", "./assets/fonts/pixel.ttf", 32.0) then 
	print("Added Font [pixel] to Asset Manager successfully")
else
	print("Failed to add the [pixel] font to the Asset Manager.")
end

Sample Lua Load Assets Function

-- Sample Assets table
AssetDefs = 
{
	textures = 
	{
		{ name = "test_texture", path = "assets/textures/test_texture.png", pixel_art = true },	
	},
	music = 
	{
		{ name = "test_music", path = "assets/music/test_music.mp3" },	
	},
	sound_fx = 
	{
		{ name = "test_sound", path = "assets/soundfx/test_sound.wav"},
	}
}

-- Sample LoadAssets function takes in the above assets table and loads 
-- the entries into the AssetManager
function LoadAssets(assets)
	for k, v in pairs(assets.textures) do
		if not AssetManager.add_texture(v.name, v.path, v.pixel_art) then
			print("Failed to load texture [" ..v.name .."] at path [" ..v.path .."]")
		else
			print("Loaded Texture [" ..v.name .."]")
		end
	end

	for k, v in pairs(assets.music) do 
		if not AssetManager.add_music(v.name, v.path) then 
			print("Failed to load music [" ..v.name .."] at path [" ..v.path .."]")
		else
			print("Loaded music [" ..v.name .."]")
		end
	end

	for k, v in pairs(assets.sound_fx) do
		if not AssetManager.add_soundfx(v.name, v.path) then
			print("Failed to load soundfx [" ..v.name .."] at path [" ..v.path .."]")
		else
			print("Loaded soundfx [" ..v.name .."]")
		end
	end
	-- TODO: Add other loading of assets as needed
end

Entity Component System

For our ECS we are using wrappers around the wonderful battle tested ENTT library! We have lua bindings for the registry, so we can get runtime views, entities, components and more.

• Registry
• Entity

Registry

TODO:

Functions

Runtime View Runtime views iterate over all of the entities that have all the given components that are passed into the function.

Registry

Example

	-- Get all the entities that have a Transform and Sprite Component
	-- Exclude entities with UI Components
	local view = Registry.get_entities(Transform, Sprite).exclude(UIComponent)

	-- Loop through the view and hide all of the sprites
	view:for_each(
		-- The for_each function takes in a callback function
		function (entity)
			local sprite = entity:get_component(Sprite)
			sprite.bHidden = true
		end
	)

Entity

An entity is a game object that consists of a unique id number and is created and monitored by the Registry. Each entity can have various components. What this means is that there are pools of components and those components are owned by each of the specific entity ids.

Even though the entity is just an ID, our implementation of the entity uses an entt::entity as it's id and also has some built in functions that we can use.

By default each entity has a name and a group to aid in the identification of the entity. We can use the name or the group to filter the entities more thoroughly. See the below example:

-- Grab all the entities that have a sprite component
local view = Registry.get_entities(Sprite)

-- Create a simple table that will hold all the enemy entities
local Enemies = {}

-- Loop through the view and place all of the entities that
-- have a group name of "enemy" into the table
view:for_each(
	function (entity)
		if entity:group() == "enemy" then
			table.insert(Enemies, Entity(entity:id()))
		end
	end
)

-- Loop through the enemies and do some work
for k, v in ipairs(Enemies) do 
	local get transform = v:get_component(Transform)
	-- ...More work here with the enemies
end

Contstructors

-- Create a new entity
local entity = Entity("name", "group")

-- Create a duplicate lua entity from the previous entity's id
local entityDupe = Entity(entity:id())

Components

This is a list of the components that can be used with the engine and their available functions and member variables.

• Transform
• Sprite
• Animation
• BoxCollider
• CircleCollider
• PhysicsComp

Transform

The transform component contains the position, rotation, and scale of the entity.

Properties:

Use Example:

-- Create a new entity
local entity = Entity("tag", "group")

-- Add a new transform component at position [50, 50], scale of 1 and no rotation. 
local transform = entity:add_component(Transform(vec2(50, 50), vec2(1, 1), 0.0))

-- access the transform properties
transform.position = vec2(100, 100)
transform.scale = vec2(2, 1)
transform.rotation = 45.0

Sprite

The sprite component contains all of the necessary properities for the sprite of an entity. A spirte has a width, height, layer, start_x, start_y, texture_name and UV values.

Properties:

Functions:

Use Example:

-- Create a new entity
local entity = Entity("tag", "group")

-- Add a new sprite component
local sprite = entity:add_component(
	Sprite(
		"hero_sprite",	-- texture_name
		32,		-- width 
		32,		-- height
		0, 		-- start_x
		0,		-- start_y
		2		-- layer
	)
)

-- After the sprite is created, you have to generate the uvs
sprite:generate_uvs()

Animation

The animation component is used to animate the sprite. It assumes that the sprite is part of a texture atlas and will adjust the current uv values based on the current frame.

Properties:

Functions:

Use Example:

-- Create a new entity
local entity = Entity("tag", "group")

-- Add a new animation component
local animation = entity:add_component(
	Animation(
		4,		-- Number of frames 
		15,		-- Frame Rate
		0,		-- Frame Offset
		false,	-- bVertical == false == horizontal scroll
		true	-- Looped
	)
)

BoxCollider

The box collider is an axis-aligned rectangle that is used for collision detection. The collider positions itself based on the entity's Transform position.

Properties:

Use Example:

-- Create a new entity, if not already created.
local entity = Entity("tag", "group")

-- Add a new transform component at position [50, 50], scale of 1 and no rotation. 
local boxCollider = entity:add_component(
	BoxCollider(
		32,			-- width
		32,			-- height
		vec2(0, 0)		-- offset
	)
)

CircleCollider

The circle collider 2D circle that is used for collision detection. The collider positions itself based on the entity's Transform position.

Properties:

Use Example:

-- Create a new entity, if not already created.
local entity = Entity("tag", "group")

-- Add a new transform component at position [50, 50], scale of 1 and no rotation. 
local circleCollider = entity:add_component(
	CicleCollider(
		16,			-- radius
		vec2(0, 0)		-- offset
	)
)

Physics Component

The physics component controls all of the physics properties of an entity.

• BodyType
• PhysicsAttributes
• PhysicsComp
• Functions
  • linear_impulse
  • angular_impulse
  • set_linear_velocity
  • get_linear_velocity
  • set_angular_velocity
  • get_angular_velocity
  • set_gravity_scale

BodyType:

The rigid body type is an enum that is used to determine the type of body to be used. These are based on the Box2D b2BodyType. There are three rigid body types to choose from:

• STATIC
  • Static bodies cannot be moved by other bodies. All movement must be done by the user.
• KINEMATIC
  • Similar to a static body, that it is not affected by dynamic bodies; however, kinematic bodies can move. Perfect for moving platforms or walls.
• DYNAMIC
  • Dynamic bodies are movable and will consume all the affects of forces and other bodies.

Use Example:

-- The use of the BodyType enum can be used as follows.
BodyType.Static 
BodyType.Kinematic
BodyType.Dynamic

-- These are normally used when creating the Physics Attributes. 
-- This will set the body type so the physics system knows how it should react to the body.

PhysicsAttributes:

These are the attributes that make up the Physics Component.

Properties:

Use Example:

-- Create a default Physics Attributes object
local physicsAttribs = PhysicsAttributes()

-- Adjust properties to desired values, properties that are unchanged use default
physicsAttribs.eType = BodyType.Dynamic
physicsAttribs.density = 100.0			-- Set the density to 100 kg/m^2
physicsAttribs.friction = 0.2			-- Set the coefficient of friction to 0.2
physicsAttribs.restitution = 0.1		-- Set the coefficient of restitution to 0.2
physicsAttribs.radius = circle.radius 		-- Use the entity's CircleCollider radius
physicsAttribs.gravityScale = 2.0		-- Multiply the force of gravity by 2.0
physicsAttribs.position = transform.position	-- Use the entity's Transform position
physicsAttribs.scale = transform.scale		-- Use the entity's Transform scale
physicsAttribs.bCircle = true			-- Make the Fixture a circle
physicsAttribs.bFixedRotation = false		-- Allow rotation

PhysicsComp:

The actual physics component that can be added to the entity. The PhysicsComp takes in the PhysicsAttributes in order to create the underlying body, fixtures and set thier initial values. The user cannot access the actual physics body; however, has access to functions that will apply the desired changes to the rigid body.

Functions:

linear_impulse

Example:

-- Get the physics component from the entity
local physics = entity:get_component(Physics)

-- Apply a linear impulse 
physics:linear_impulse(vec2(10000, 100))

angular_impulse

Example:

-- Get the physics component from the entity
local physics = entity:get_component(Physics)

-- Apply an angular impulse 
physics:angular_impulse(45)

set_linear_velocity

Example:

-- Get the physics component from the entity
local physics = entity:get_component(Physics)

-- Move the entity to the right with a velocity of 50 
physics:set_linear_velocity(vec2(50, 0))

get_linear_velocity

Example:

-- Get the physics component from the entity
local physics = entity:get_component(Physics)

-- Get the linear velocity
local velocity = physics:get_linear_velocity()

set_angular_velocity

Example:

-- Get the physics component from the entity
local physics = entity:get_component(Physics)

-- Set the angular velocity
physics:set_angular_velocity(60)

get_angular_velocity

Example:

-- Get the physics component from the entity
local physics = entity:get_component(Physics)

-- Get the angular velocity or Omega
local omega = physics:get_angular_velocity()

set_gravity_scale

Example:

-- Get the physics component from the entity
local physics = entity:get_component(Physics)

-- Set the angular velocity
physics:set_gravity_scale(2.0)

Music and SoundFx

The Music and Sound players allow the user to play their desired music or sounds in the game. By default, there are 16 channels available to the user to use. There is only one channel that is dedicated for music, meaning that we can only have one music song playing at a time.

Music Player

The music player will only play sounds that have already been loaded into the Asset Manager. The music player is automatically opened when the engine boots up.

• Valid music file formats:
  • MP3
  • WAV
  • OGG

Functions:

play

Example:

-- Play the title music
Music.play("title", -1) -- play the title music and loop continuously.

top

stop

Example:

-- Stop the music
Music.stop()

top

pause

Example:

-- Pause the music
Music.pause()

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resume

Example:

-- Resume the music
Music.resume()

top

set_volume

Example:

-- Set the volume to 50%
Music.set_volume(50)

top

is_playing

Example:

-- Check if the music player is playing.
if Music.is_playing() then 
	Music.set_volume(50)
end

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Sound Player

The sound player is used when we want small chunk soundFx played. The Sound Player, like the Music Player will only play sounds that have already been loaded into the Asset Manager. However, unlike the music player, the user must specify the channel that we want the music to be played on.

If the user chooses -1 for the channel, the sound FX will be played on any open channel. There there are no open channels, the Sound Player will log an error.

• Valid sound fx file formats:
  • MP3
  • WAV

Functions:

play

Example:

-- Play the sword_slash soundFX
Sound.play("sword_slash", 0, -1) -- Don't loop and play on any open channel.
Sound.play("sword_slash")	-- Same as above; however, uses the default values.

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stop

Example:

-- Stop channel 5
Sound.stop(5)

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set_volume

Example:

-- Set the volume off all channels to 50%
Sound.set_volume(-1, 50)

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Input Management

Keyboard

Currently, there can only be one keyboard present at any time. Users can use the keyboard inputs to control game actions, such as:

• Player Movement
• Menu Selections
• and much more

Mapped Keys:

Here is a list of the mapped keys and their names when using the keyboard:

Registerd Typewriter Keys

KEY_A	KEY_B	KEY_C	KEY_D	KEY_E	KEY_F	KEY_G	KEY_H
KEY_I	KEY_J	KEY_K	KEY_L	KEY_M	KEY_N	KEY_O	KEY_P
KEY_Q	KEY_R	KEY_S	KEY_T	KEY_U	KEY_V	KEY_W	KEY_X
KEY_Y	KEY_Z	KEY_C	KEY_D	KEY_E	KEY_F	KEY_G	KEY_H

KEY_0	KEY_1	KEY_2	KEY_3	KEY_4	KEY_5	KEY_6	KEY_7
KEY_8	KEY_9

KEY_ENTER	KEY_BACKSPACE	KEY_ESC	KEY_SPACE	KEY_LALT	KEY_LSHIFT
KEY_LCTRL	KEY_RCTRL	KEY_RALT	KEY_RSHIFT

Registerd Function Keys

KEY_F1	KEY_F2	KEY_F3	KEY_F4	KEY_F5	KEY_F6	KEY_F7	KEY_F8
KEY_F9	KEY_F10	KEY_F11	KEY_F12

Registerd Cursor Control Keys

KEY_UP	KEY_RIGHT	KEY_DOWN	KEY_LEFT

Keyboard Functions:

Example Usage:

local physics = entity:get_component(Physics)

-- Set the linear velocity of the entity based on the WASD keys
if Keyboard.pressed(KEY_W) then 
	physics:set_linear_velocity(vec2(0, 50))
elseif Keyboard.pressed(KEY_S) then 
	physics:set_linear_velocity(vec2(0, -50))
elseif Keyboard.pressed(KEY_A) then 
	physics:set_linear_velocity(vec2(-50, 0))
elseif Keyboard.pressed(KEY_D) then 
	physics:set_linear_velocity(vec2(50, 0))
end 

-- Have the entity jump if space bar is pressed 
if Keyboard.just_pressed(KEY_SPACE) then 
	physics:linear_impulse(vec2(0, -10000)
end 

Mouse

Gamepad

The gamepad is based on an XBox-style gamepad. Scion2D supports up to 4 controllers/gamepads. The gamepad usually will have two analog thumb sticks, a D-Pad, four face buttons, two shoulder buttons, two analog trigger buttons, and two center buttons.

Action Buttons

Special Buttons

Axes

The axes are buttons and joysticks that use analog input values rather than a digital/bool input.

Hat Values

Not all controllers have hats. The hat is basically the DPAD; however, it also has the diagonal directions. We use the hat values based on a number that is returned depending on the direction that is pressed. The typical hat values are as follows:

Functions:

All of the controller functions take the index of which controller is being used. We are allowed up to 4 controllers in the engine. The index is basically the SLOT of the controller.

Examples

Left Stick Analog

	-- Get current x speed from the analog value
	local x_analog = Gamepad.get_axis_position(1, AXIS_X1) 
	local x_multiplier = x_analog / 32768
	local x_speed = speed * x_multiplier

	-- Get current y speed from the analog value
	local y_analog = Gamepad.get_axis_position(1, AXIS_Y1) 
	local y_multiplier = y_analog / 32768
	local y_speed = speed * y_multiplier

	-- Set the linear velocity
	local physics = entity:get_component(Physics)
	physics:set_linear_velocity(x_speed, y_speed)
	
	-- This does not take into consideration the dead zone of the axis
	-- The dead zone varies from controller to controller

Using hat values for movement

	-- Get the hat value for controller 1
	local direction = Gamepad.get_hat_value(1)
	
	-- move the player based on the current hat value
	if direction == 0 then 
		-- TODO: Stop the player
	elseif direction == 1 then 
		-- TODO: Move the player up
	elseif direction == 2 then 
		-- TODO: Move the player right
	elseif direction == 3 then 
		-- TODO: Move the player up to the right
	elseif direction == 4 then 
		-- TODO: Move the player down
	elseif direction == 6 then 
		-- TODO: Move the player down to the right
	elseif direction == 8 then 
		-- TODO: Move the player left
	elseif direction == 9 then 
		-- TODO: Move the player up to the left
	elseif direction == 12 then 
		-- TODO: Move the player down to the left
	end

	-- This is a simplification of what we could use
	-- the hat values for.

Using just_pressed for UI

	if Gamepad.just_pressed(1, GP_DPAD_UP) then 
		-- Move cursor up
	elseif Gamepad.just_pressed(1, GP_DPAD_RIGHT) then 
		-- Move cursor right
	elseif Gamepad.just_pressed(1, GP_DPAD_DOWN) then 
		-- Move cursor down
	elseif Gamepad.just_pressed(1, GP_DPAD_LEFT) then 
		-- Move cursor left
	end

Camera

The camera is a simple 2D camera that uses orthographic projection under the hood. You can use the camera to adjust the position of the game world, convert screen coordinates to world coordinates, zoom in and zoom out by setting the scale of the camera, and more.

The user cannot current create there own instance of the camera; however, they can access the main camera and use the functions provided.

The camera is basically a Rect that will show what is inside of it. It has a position, scale, width, and height.

TODO: Eventually, all games will have a settings file to allow the creator to adjust the camera width/height, along with the window width for each game. That is currently under construction.

Functions:

Examples

Move Camera Position

	-- Get an instance of the camera
	local cam = Camera.get()
	
	-- Get the camera position, since it does not have a ctor
	-- we use the '.' operator rather than the ':'.
	local cam_pos = cam.position()

	-- Move the camera in the x direction on every update
	cam.set_position(vec2(cam_pos.x + 10, cam_pos.y))

Set Camera Scale

	-- Get an instance of the camera
	local cam = Camera.get()
	
	-- Set the camera scale to 4. This will zoom in by 4x. 
	-- So if the sprite is 16x16px, it will now look 64x64px.
	cam.set_scale(4.0)

These functions will control the main camera. If you want to use the camera to follow a specific player or entity, try to make use of the Follow Camera or create a lua class that will control the camera any way you see fit.

Follow Camera

The FollowCamera can be used to follow the movement of a specific character or entity in your game.

FollowCamParams

The follow camera params are the parameters that are used to help control the follow camera.

Properties:

Examples

	-- There are two ctors for FollowCamParams
	-- First takes a lua table {}
	local followCamParams1 = FollowCamParams(
		{
			min_x = 0,
			min_y = 0,
			max_x = WindowWidth(),	-- Get the Window Width from the engine
			max_y = WindowHeight(),	-- Get the Window Height from the engine
			scale = 4.0,		-- Set the camera scale to 4 
			springback = 0.2		-- Follow slightly behind the character
		}
	)

	-- The Second ctor uses arguments
	local followCamParams2 = FollowCamParams(
		0, 0, WindowWidth(), WindowHeight(), 4.0, 0.2
	)

FollowCamera Functionality

In order to create a new follow camera, we need to pass in the Desired FollowCamParams and the Entity that we want the camera to follow.

Example

	-- Create a new followCam 
	local followCam = FollowCamera(
		FollowCamParams(0, 0, WindowWidth(), WindowHeight(), 4.0, 0.5),
		playerEntity -- We need to pass in the entity we want the camera to follow.
	)
	
	-- We need to always update the camera in our main update loop
	-- This will ensure that the camera is following the player's
	-- movement
	followCam:update()

Lua Functions

• Functions

  • S2D_RunScript
  • S2D_LoadScriptTable
  • S2D_MeasureText

• Logging Functions

  • S2D_log
  • S2D_warn
  • S2D_error

• Physics Functions

  • S2D_EnablePhysics
  • S2D_DisablePhysics
  • S2D_IsPhysicsEnabled

• Render Collider Functions

  • S2D_EnableCollisionRendering
  • S2D_DisableCollisionRendering
  • S2D_CollisionRenderingEnabled

S2D_RunScript

Example:

-- Run the script list table
if not S2D_RunScript("scipts/script_list.lua") then 
	S2D_error("Failed to run lua script")
end

S2D_LoadScriptTable

Example:

-- Script List Example
ScriptList = 
{
	"game/scripts/assetDefs.lua",
	"game/scripts/utilities.lua",
	"game/scripts/player.lua",
	-- ... More scripts here
}

-- Run all the scripts in the table 
S2D_LoadScriptTable(ScriptList)

S2D_MeasureText

Example:

-- Script List Example

local transform = entity:get_component(Transform)
local text = entity:get_component(TextComponent)
local textWidth = S2D_MeasureText(text.textStr, text.fontName)

-- Center the entity to the window width 
transform.position = (S2D_WindowWidth() * 0.5) - (textWidth * 0.5)

Logging Functions

These logging functions use the common placeholder and formatting options:

S2D_log

Example:

-- Logging Example

S2D_log("My name is %s. I am %d years old", "Scion", 2)

S2D_warn

Example:

-- Warning Example

Names = 
{
	"Jack", "Jill", "Steve"
}

local nameToFind = "Scion"
local bFound = false 

for _, v in pairs(Names) do 
	if v == nameToFind then 
		bFound = true 
		break
	end 
end 

if not bFound then
	S2D_warn("This name [%s] could not be found.", nameToFind)
else
	S2D_log("This name [%s] was found successfully.", nameToFind)
end

S2D_error

Example:

Assets = 
{
	Textures = 
	{
		{ name = "hero", path = "./assets/textures/hero.png", bPixelArt = true },
		-- ... More Textures
	},
	Sounds = 
	{
		-- Add sounds
	}
}

-- Error Example

for k, v in pairs(Assets.Textures) do
	if AssetManager.add_texture(v.name, v.path, v.bPixelArt ) then 
		S2D_log("Added texture [%s] successfully", v.name)
	else
		S2D_error("Failed to add texture [%s] at path [%s].", v.name, v.path)
	end
end 

Physics Functions

S2D_EnablePhysics

Example:

-- Enable Box2D Physics

S2D_EnablePhysics()

S2D_DisablePhysics

Example:

-- Disable Box2D Physics

S2D_DisablePhysics()

S2D_IsPhysicsEnabled

Example:

-- Enable Box2D Physics

S2D_DisablePhysics()

Render Collider Functions

S2D_EnableCollisionRendering

Example:

-- Show Box/Circle Colliders

S2D_EnableCollisionRendering()

S2D_DisableCollisionRendering

Example:

-- Hide Box/Circle Colliders

S2D_DisableCollisionRendering()

S2D_CollisionRenderingEnabled

Example:

-- Check to see if Collision rendering is enabled
if S2D_CollisionRenderingEnabled then 
	S2D_DisableCollisionRendering()
end 

Editor

• Project Hub

Project Hub

The Project Hub is used for creating a new project or loading a previously created project.

Creating a New Project

In order to create a new project, you first want to press the New Project button. This will open up a new page that will allow you to name your project and set the projects path.

By default, the editor will create a folder [ScionProjects] directly wherever the editor's executable is located for projects. This folder is just a suggestion and does not have to be used. If you would like to set a new location, press the Browse button to open the folder dialog and set the desired folder you wish to use.

Once the project path has been set, all you need to do now is add in the desired name of the project and then press the Create button.

When the project is created, there are different folders and files automatically created for you.

Generated Folders

Generated Files

The main project file or .s2dprj is just a JSON file underneath; however, the editor expects the file to contain specific content in order to work correctly. You should not have to make changes to this file because it should be created automatically upon project creation and updated every time the project is saved.

--[[
	Main Lua script. This is needed to run all scripts in the editor
	GENERATED BY THE ENGINE ON PROJECT CREATION. DON'T CHANGE UNLESS 
	YOU KNOW WHAT YOU ARE DOING!
--]]

-- The engine looks for these two functions.
-- Please add your code inside of the update and render functions as needed.
main = { 
	[1] = { 
		update = function() 
			-- Add your code to be update here
		end
	}, 
	[2] = { 
		render = function() 
			-- Add any extra rendering code here
		end
	}, 
}

You do not have to write all of your code inside of the main.lua file. It can all be separate scripts. For instance, if you create different game states in different files, you would only want to call the Update function of the current state inside of this update function. The rest of the code can be written in the loaded scripts. In order to load separate scripts, see Lua Functions for an example.