flickyclone/flickyclone.org

Literate Flicky Clone

• Flicky
• Set up
• Dependencies
• Classy objects
• (2D) Vector Math
• Helper functions
• Swept AABB
• Broad-Phasing collisions with solid tiles
• Game states
• Debugging
• Map class
• Tile class
• Entity class
• Enemy class
• Initialization
• Game logic
• Updating each frame
• Drawing to the screen
• Ideas
• Devlog
  • [2024-08-17 sáb]
  • [2024-09-02 lun]
  • [2024-09-24 mar]
• Plan
  • Install dependencies (inspect, debugger) through luarocks
  • Create object base "class" with copy metamethods functionality, explain literarily
  • Refactor Object:new, Object:init, introduce Object:extend
  • Convert acceleration to vector in Entity:move
  • Fix gravity always changing position in y axis on Entity:move
  • Add grounded attribute to player/entity
  • love.load()
  • Bugfix drawing offset by 1 in x and y
  • love.update(dt)
  • love.draw()
  • Level wrap-around
  • Bugfix level wrap-around
  • Update "literary" parts
  • Player slide
  • changing direction while in mid air should have lots of friction
  • Bugfix Enemy:draw not working
  • Refactor player, enemies, items code into entities
  • Add a couple enemy entities with stupid AI
  • Title screen art mock
  • Gameplay screen art mock
  • Fix Tile class ipairs
  • Collision with platforms above when jumping
  • Camera fixed on player position
  • Implement game states
  • Explain game object components
  • Refine player movement
  • Bugfix scaling and/or drawing
  • Maybe create a game class, player class, etc.
  • Explain 320x200 resolution
  • Fix aspect ratio
  • Bugfix jump code
  • Set up some kind of debug mode (toggle?)
  • Define enemy spawner logic (a few different options)
  • Map player position correctly when drawing
  • Create lower-resolution internal game model
  • Consider dropping game.world and not using STI's box2d support
  • Draw debug helpers
  • Draw platforms from game.platforms table
  • slide animation when direction button is released
  • Generic Object:copy method
  • Decouple GameState objects, map (maybe), and graphics
  • Fix collision with solid tile when moving horizontally
  • Implement game pause as Play substate
  • replace hardcoded player initial position (180, 100) with marker/point from Tiled map
  • Reimplement draw_debug_infos
  • Fix jump
  • Bugfix ceiling bump teleport
  • Try implementing wrap-around with polar coordinates and cosine

Flicky

I love Flicky, it's such a tight fun arcade game. I'm going to attempt to clone it using LÖVE and literate programming to note down my ideas and plans, and also explain the code a bit.

It's unlikely this will ever be published, but I'm hoping to make more games in the future this way, and improve until I'm confident enough to put them up on the interwebs.

Set up

I'll start off with a small conf.lua file, specifying the LÖVE version, the game title, and that it should run in full screen by default:

  function love.conf(t)
     t.version = "11.4"
     t.window.fullscreen = true
     t.title = "Literate Flicky Clone"
  end

Dependencies

I won't be using many dependencies, instead trying to code stuff on my own and using LÖVE's libraries sparingly. This is mainly because I like learning what makes games tick, but also I typically find LÖVE-related libraries hard to use and unnecessarily complicated, as well as poorly documented.

That being said, I do find inspect to be quite useful (I believe it should be a Lua built-in.)

  local inspect = require("inspect/inspect")

Classy objects

I can't escape an object-oriented style, especially for games, not sure if this is a good or bad thing though I'd love to make a game in a more functional style, but the code for games made with LÖVE I read so far are all OO. I mainly need "classy objects" for inheritance, I find that to be a great way to re-use code while providing a lot of flexibility.

Lua doesn't have classes though, but it does have objects with prototype capabilities through their metatable property, which allow implementing something close to inheritance. Let's create a base Object "class" which allows inheritance.

Object will have a new method which will create new instances. This is achieved by first setting Object as its own __index metamethod and then setting Object as the metatable of a new, empty Lua table. This has the effect of fields not present in the new table to be looked up in Object (mainly for looking up methods). All of that is encapsulated in an Object:new function:

  local inspect = require("inspect/inspect")
  local Object = {}
  Object.__index = Object

  function Object:new(...)
     local object = setmetatable({__index=self}, self)
     object.__class = self
     object:init(...)
     return object
  end

new calls an init method ala Python to allow subclasses to initialize themselves taking arbitrary arguments. Object's initializer simply keep a copy of the arguments being passed in.

    function Object:init(...)
  	 self.__args = {...}
    end

Now, inheritance will be a simple interface, an extend function that takes care of creating a new "class" (a Lua table) and copying all metamethods in the parent's metatable (except __index and any metamethod it already has) to it:

  function Object:extend(SubClass)
     SubClass = SubClass or {}
     for k, v in pairs(self) do
  	  if k:match("^__") then
  		 SubClass[k] = v
  	  end
     end
     SubClass.__index = SubClass
     SubClass.__super = self
     return setmetatable(SubClass, self)
  end

Also, we'll set a handy __super reference to the parent class, so subclasses can call its methods when extending them, enabling polymorphism.

I figured out enough of this on my own, but later found this written a lot better (and took lots of idead from) in different places:

• Eevee's klingklang engine
• Curse of the Arrow
• Hump
• Classic

Finally, return this for module imports:

  return Object

(2D) Vector Math

This will be a good project to (re)learn vector math and its application to physics stuff on videogames.

Let's start with the vector class extending Object:

  local inspect = require("inspect/inspect")
  local Object = require("object")

  local Vector = Object:extend()

Vector's initializer will take an x and y value and store them as attributes, and also compute its angle from them.

  function Vector:init(x, y)
     Vector.__super.init(self, x, y)
     self.x = x
     self.y = y
     self.angle = math.atan2(self.x, self.y)
  end

Next, we'll define mathematical operations by extending Lua's metamethods, to get nice stuff like vector1 + vector2, number*vector, #vector to get its length, etc.

  function Vector:__add(v)
  	 return self.__class:new(self.x + v.x, self.y + v.y)
  end

  function Vector:__sub(v)
  	 return self.__class:new(self.x - v.x, self.y - v.y)
  end

  function Vector:__mul(obj)
  	 if getmetatable(obj) == Vector then
  		-- dot product
  		return self.x*obj.x + self.y*obj.y
  	 else
  		-- scalar product
  		return self.__class:new(self.x*obj, self.y*obj)
  	 end
  end

  function Vector:__eq(v)
     return self.x == v.x and self.y == v.y
  end

  function Vector:__lt(v)
  	 return self.x < v.x and self.y < v.y
  end

  function Vector:__le(v)
  	 return self.x <= v.x and self.y <= v.y
  end

  function Vector:__gt(v)
  	 return self.x > v.x and self.y > v.y
  end

  function Vector:__ge(v)
  	 return self.x >= v.x and self.y >= v.y
  end

  function Vector:__unm()
  	 return self.__class:new(-self.x, -self.y)
  end

  function Vector:__len() -- magnitude
  	 return math.sqrt(self.x^2 + self.y^2)
  end

  function Vector:normalize()
  	 return self.__class:new(self.x/#self, self.y/#self)
  end

  -- Method to get the clockwise normal of the vector
  function Vector:normal_cw()
  	 return self.__class:new(self.y, -self.x)
  end

  -- Method to get the counterclockwise normal of the vector
  function Vector:normal_ccw()
  	 return self.__class:new(-self.y, self.x)
  end

  return Vector

  local Vector = require("vector")

Helper functions

Let's create a module to contain helper functions:

  local helpers = {}

For whatever reason Lua doesn't have a sign function 🤷, let's define our own:

  function helpers.sign(n)
     if n == 0 then
  	  return 0
     end
     return math.abs(n)/n
  end

Same with rounding numbers, need our own function for that:

  function helpers.round(num)
     return num >= 0 and math.floor(num + 0.5) or math.ceil(num - 0.5)
  end

Let's define a bound function to keep a value within bounds

  function helpers.bound(value, min, max)
     if value and value < min then
  	  return min
     elseif value and value > max then
  	  return max
     else
  	  return value
     end
  end

I think a functional map function can be helpful when loading the map and similar stuff

  function helpers.map(tbl, fun)
     local result = {}
     for i, v in ipairs(tbl) do
  	  result[i] = fun(v)
     end
     return result
  end

But map would feel too lonely being the only functional function around, let's also add filter:

  function helpers.filter(tbl, fun)
     local result = {}
     for i, v in ipairs(tbl) do
  	  if fun(v) then
  		 table.insert(result, v)
  	  end
     end
     return result
  end

To achieve Flicky's screen wrap-around trick (or part of it at least), we'll start with a normalize function that given a number n, it returns a new n that's within a range offset the original n, so if the screen's width is 100, and n is 110, normalizing it would result in 10, if that makes sense:

  function helpers.normalize(n, min, max)
     local range = max - min
     return ((n - min) % range + range) % range + min
  end

I'm planning on later replacing that with polar coordinates instead, think of levels being drawn on a cylinder, and the player seamlessly moving around it, so normalize will hopefully go away in the future.

We'll need a function to tell if two rectangles overlap for basic collision detection, with rectangles being Lua tables with these field names:

x

horizontal pixel position

y

vertical pixel position

w

width in pixels

h

height in pixels

  function helpers.rectangles_overlap(rect1, rect2)
	 local x_overlaps = rect1.x < rect2.x + rect2.w and rect1.x + rect1.w > rect2.x
	 local y_overlaps = rect1.y < rect2.y + rect2.h and rect1.y + rect1.h > rect2.y
	 return {x_overlaps and y_overlaps, x_overlaps, y_overlaps}
  end

Finally return the helpers object containing all those functions, and load it from main:

  return helpers

  local helpers = require("helpers")

Swept AABB

This is not being used yet, but I'm keeping it for now since I believe it'll be useful for better collision handling at high speeds, like falls, or enemies going directly at the player.

This is what I ended up learning with more difficulty than I expected. I could probably get away with something simpler for this game, but I want to learn as much as I can.

In any case, the idea here is to detect two rectangles colliding and avoid the "tunneling" problem where rectangles moving at a high enough velocity move past each other rectangles that should have collided.

I read a bunch of articles, but I'm now following one from gamedev.net, let's try and translate to Lua:

  function swept_aabb(box1, box2, dt)
	 local x_inv_entry, y_inv_entry, x_inv_exit, y_inv_exit
	 if box1.dx > 0 then
		x_inv_entry = box2.x - (box1.x + box1.w)
		x_inv_exit = (box2.x + box2.w) - box1.x
	 else
		x_inv_entry = (box2.x + box2.w) - box1.x
		x_inv_exit = box2.x - (box1.x + box1.w)
	 end
	 if (box1.dy > 0) then
		y_inv_entry = box2.y - (box1.y + box1.h)
		y_inv_exit = (box2.y + box2.h) - box1.y
	 else
		y_inv_entry = (box2.y + box2.h) - box1.y
		y_inv_exit = box2.y - (box1.y + box1.h)
	 end

	 local x_entry_time, y_entry_time, x_exit_time, y_exit_time
	 if (box1.dx == 0) then
		x_entry_time = -math.huge
		x_exit_time = math.huge
	 else
		x_entry_time = x_inv_entry / box1.dx
		x_exit_time = x_inv_exit / box1.dx
	 end
	 if (box1.dy == 0) then
		y_entry_time = -math.huge
		y_exit_time = math.huge
	 else
		y_entry_time = y_inv_entry / box1.dy
		y_exit_time = y_inv_exit / box1.dy
	 end
	 local entry_time = math.max(y_entry_time, x_entry_time)
	 local exit_time = math.min(y_exit_time, x_exit_time)
	 local normalx, normaly
	 if (entry_time > exit_time or x_entry_time < 0 and y_entry_time < 0 or x_entry_time > 1 or y_entry_time > 1) then
		normalx = 0
		normaly = 0
		entry_time = 1
	 else
		if x_entry_time > y_entry_time then
		   if x_inv_entry < 0 then
			  normalx = 1
			  normaly = 0
		   else
			  normalx = -1
			  normaly = 0
		   end
		else
		   if y_inv_entry < 0 then
			  normalx = 0
			  normaly = 1
		   else
			  normalx = 0
			  normaly = -1
		   end
		end
	 end
	 print("SWEPT AABB TIME:", entry_time )
	 return {normal={x=normalx, y=normaly}, dt=entry_time}
  end

Broad-Phasing collisions with solid tiles

This is also not wired into the game just yet, although I'm not sure this will be needed, so I may end up removing it.

This basically comes down to finding the (solid) tiles within the rectangle determined by the initial and final positions of an entity (the player for now).

First, let's write a function to get that displacement rectangle:

  function get_displacement_rect(entity, next_pos)
	 local displacement_rect = {
		x=entity.x,
		y=entity.y,
		w=entity.w,
		h=entity.h,
	 }
	 if entity.dx > 0 then
		displacement_rect.x = entity.x
		displacement_rect.w = next_pos.x + entity.w - entity.x
	 elseif entity.dx < 0 then
		displacement_rect.x = next_pos.x
		displacement_rect.w = entity.x + entity.w - next_pos.x
	 end

	 if entity.dy > 0 then
		displacement_rect.y = entity.y
		displacement_rect.h = next_pos.y + entity.h - entity.y
	 elseif entity.dy < 0 then
		displacement_rect.y = next_pos.y
		displacement_rect.h = entity.y + entity.h - next_pos.y
	 end
	 return displacement_rect
  end

Next, we'll need a function that returns a list of rectangles representing tiles found in the displacement rectangle:

  function distance(point_a, point_b)
	 return math.sqrt(math.pow(point_a.x - point_b.x, 2) + math.pow(point_a.y - point_b.y, 2))
  end
  function find_closest_tile_in_rectangle(entity, rect, game)
	 local closest
	 local center = {x=entity.x + entity.w/2, y=entity.y + entity.h/2}
	 local min_distance = math.huge
	 local top_left_tile = game:pixel_to_tile(rect)
	 local bottom_right_tile = game:pixel_to_tile({
		   x=rect.x + rect.w,
		   y=rect.y + rect.h,
	 })
	 for tx=top_left_tile.x, bottom_right_tile.x do
		for ty=top_left_tile.y, bottom_right_tile.y do
		   local value = game:tile_value({x=tx, y=ty})
		   if value ~= 0 then
			  local tile_center = {x=game:x_to_pixel(tx) + game.map.tilewidth/2, y=game:y_to_pixel(ty) + game.map.tileheight/2}
			  local current_distance = distance(center, tile_center)
			  if current_distance < min_distance then
				 closest = {x=game:x_to_pixel(tx), y=game:y_to_pixel(ty), w=game.map.tilewidth, h=game.map.tileheight, value=value, tx=tx, ty=ty}
				 min_distance = current_distance
			  end
		   end
		end
	 end
	 return closest
  end

Game states

I'm thinking there should be at least 4 game states:

• Title screen
• Play
• Game Over
• Ending

Let's start with the base GameState class, it should keep the shared logic of initialization, updating the input state, as well as drawing to the screen:

  local Object = require("object")
  local Entity = require("entity")
  local Enemy = require("enemy")
  local Map = require("map")
  local helpers = require("helpers")

  local GameState = Object:extend()

  function GameState:init()
     GameState.__super.init(self)
     self.input = {
  	  start=false,
  	  right=false,
  	  left=false,
  	  up=false,
  	  down=false,
  	  jump=false,
     }
     self.ended = false
     self.next = nil
  end

  function GameState:updateInput(dt)
     self.input.start = love.keyboard.isDown("return")
     self.input.right = love.keyboard.isDown("d", "right")
     self.input.left = love.keyboard.isDown("a", "left")
     self.input.up = love.keyboard.isDown("w", "up")
     self.input.down = love.keyboard.isDown("down", "s")
     self.input.jump = love.keyboard.isDown("space")
  end

  function GameState:update(dt)
     self:updateInput(dt)
  end

  function GameState:draw()
  end

The first state (for now, we may later add a splash screen or similar) the game will be in is the title screen, from which the player can start the game or go to other states like options, cheats, etc. This boils down to extending the GameState:update method to check the start button is pressed, in which case it'll create the next state to switch to, Play:

  local Title = GameState:extend()

  function Title:update(dt)
     Title.__super.update(self, dt)
     if self.input.start then
  	  print("PRESSED START ENDING THIS STATE")
  	  self.ended = true
  	  self.next = Play:new()
     end
  end

  function Title:draw()
     Title.__super.draw(self)
     local font = love.graphics.getFont()
     local height = font:getHeight()
     local width = font:getWidth("MICHI")
     love.graphics.setColor(1, 1, 1)
     love.graphics.print("MICHI", 320/2, 24, 0, 2, 2, width/2, height/2)
     width = font:getWidth("DRAGON")
     love.graphics.print("DRAGON", 320/2, 64, 0, 2, 2, width/2, height/2)
     width = font:getWidth("START")
     love.graphics.print("START", 320/2, 128, 0, 1, 1, width/2, height/2)
  end

So, let's define that Play state. Basically this takes the place of the old game object I started with in main.lua. It'll be the biggest state and probably will be split out into sub-states of its own, but for now it'll be a single level which will eventually lead to the game over and game finished states (once deaths and level progression are implemented). Right now it will load a single level in the form of an instance of the new Map class, update the player Entity state, and draw the map and player to the screen. Also, it'll spawn a couple entities for enemies that will just move around the screen.

  local Play = GameState:extend()

  function Play:init()
     Play.__super.init(self)
     self.map = Map:new("assets/map.lua")
     self.current_frame = 0
     self.physics = {
  	  gravity=self.map.tileheight*9.8,	-- somewhat exagerated gravity (3x)
  	  maxdx=self.map.tilewidth*8,		-- max horizontal speed
  	  maxdy=self.map.tileheight*24,		-- max vertical speed
  	  jump=self.map.tileheight*512,		-- instant jump impulse
     }
     self.physics.horizontal_acc = self.physics.maxdx*2	-- horizontal acceleration
     self.physics.friction = self.physics.maxdx*1.5	-- horizontal friction
     self.player_entity = Entity:new(180, 100, 4, 8, self.physics.gravity, 2*8, self.physics.horizontal_acc, self.physics.friction, self.map)
     self.enemies = {
  	  Enemy:new(16, 24, 4, 8, self.physics.gravity, 2*8, self.physics.horizontal_acc, self.physics.friction, self.map),
  	  Enemy:new(224, 24, 4, 8, self.physics.gravity, 2*8, self.physics.horizontal_acc, self.physics.friction, self.map),
  	  Enemy:new(16, 48, 4, 8, self.physics.gravity, 2*8, self.physics.horizontal_acc, self.physics.friction, self.map),
  	  Enemy:new(224, 48, 4, 8, self.physics.gravity, 2*8, self.physics.horizontal_acc, self.physics.friction, self.map),
     }
  end

  function Play:updatePlayer(dt)
     self.player_entity = self.player_entity:move(self.input, dt, self.current_frame)
  end

  function Play:updateCamera(dt)
  end
  function Play:updateItems(dt)
  end
  function Play:updateEnemies(dt)
     for i, enemy in ipairs(self.enemies) do
  	  self.enemies[i] = enemy:move({start=false, right=i%2~=0, left=i%2==0, up=false, down=false, jump=self.current_frame%7==0}, dt, self.current_frame)
     end
  end
  function Play:updateChirps(dt)
  end

  function Play:update(dt)
     Play.__super.update(self, dt)
     self.current_frame = self.current_frame + 1
     self:updatePlayer(dt)
     self:updateCamera(dt)
     self:updateItems(dt)
     self:updateEnemies(dt)
     self:updateChirps(dt)
  end

  function Play:draw()
     love.graphics.setColor(0.2, 0.2, 0.2)
     self.map:draw()
     love.graphics.setColor(0, 0.8, 0.1)
     self.player_entity:draw()
     for i, enemy in ipairs(self.enemies) do
  	  enemy:draw()
     end
  end

     <<playState>>
     <<titleState>>
     return {
  	  Play=Play,
  	  Title=Title,
     }

  local states = require("states")

Debugging

Let's add a function to draw some debug stuff, starting with just the player's position. I'll later set it up as a toggle with a key or similar.

  function game:draw_debug_infos()
	 love.graphics.setColor(0.1, 0.1, 0.1)
	 love.graphics.setFont(self.debug_font)
	 love.graphics.print("pos:("..math.floor(self.player_entity.pos.x)..", "..math.floor(self.player_entity.pos.y)..") g="..tostring(self.player_entity.grounded), 2, 2)
	 love.graphics.print(
"vel:("..math.floor(self.player_entity.vel.x)..", "..math.floor(self.player_entity.vel.y)..")", 96, 2)
	 love.graphics.print("input:(L="..tostring(self.input.left)..",R="..tostring(self.input.right)..",U="..tostring(self.input.up)..",D="..tostring(self.input.down)..",J="..tostring(self.input.jump)..")", 2, 12)
  end

Map class

I'm using the venerable Tiled to create the level(s). Tiled is so nice it exports levels as .lua files containing a big table with all the information one can need.

I'll need an interface for that though, to make it more manageable and fit my style of coding, so let's create a Map class that can provide useful functionality, such as:

• load the .lua file generated by Tiled
• spit out Tile objects that provide information such as their location and whether their solid tiles or not
• draw the whole level to the screen
• query tiles by pixel position

Of course, a Map will be an ~Object subclass:

  local Object = require("object")
  local Tile = require("tile")
  local helpers = require("helpers")
  local inspect = require("inspect/inspect")

  local Map = Object:extend()

The map will be initialized with just the path to the Tiled Lua file, which it'll load and get some metadata from. Mainly, it'll look up a "platforms" layer, which is where I'm laying out the blocks that make up a level's platforms.

  function Map:init(filename)
     Map.__super.init(self)
     local map = love.filesystem.load(filename)()
     local platform_layers = helpers.filter(map.layers, function (layer) return layer.name == "platforms" end)
     self.width = map.width
     self.height = map.height
     self.tilewidth = map.tilewidth
     self.tileheight = map.tileheight
     self.data = platform_layers[1].data
     self.max_pixel = {x=map.width*map.tilewidth, y=map.height*map.tileheight}
  end

We'll need a way to iterate through each of the platform tiles of a level. Tiled provides a single-dimension array representing each tile on the map. Each element in the array is simply a number representing the tile's index (to be mapped to a spritesheet), with 0 meaning "no tile here".

We'll translate that to instances of our Tile class which will use that value for its solid attribute.

I tried using the __ipairs metamethod to get a nice for i, tile in ipairs(map) do bit of code, but turns out __ipairs was deprecated and removed from Lua, bummer. Instead, we'll simply have a itertiles method that will do the same:

  function Map:itertiles()
     local function iterator(map, index)
  	  index = index + 1
  	  local value = map.data[index]
  	  if value ~= nil then
  		 local tx = ((index - 1) % map.width) + 1
  		 local ty = math.floor((index - 1) / map.width) + 1
  		 local tile = Tile:new(tx, ty, map.tilewidth, map.tileheight, value)
  		 return index, tile
  	  end
     end
     return iterator, self, 0
  end

Having Map:itertiles makes drawing the map to the screen super simple:

  function Map:draw()
     for i, tile in self:itertiles() do
  	  love.graphics.setColor(0.9, 0.8, 0.7)
  	  if tile.solid then
  		 love.graphics.setColor(0.2, 0.2, 0.2)
  	  end
  	  love.graphics.rectangle("fill", tile.pixel_rect.x, tile.pixel_rect.y, tile.w, tile.h)
  	  love.graphics.setColor(0.9, 0.1, 0.3)
  	  love.graphics.rectangle("line", tile.pixel_rect.x, tile.pixel_rect.y, tile.w, tile.h)
     end
  end

Finally, we'll need the map to provide the tile for a given pixel position on the screen. This will be useful for how I'm doing collision detection.

  function Map:get_tile_from_pixel(pixel)
     local tile_x = math.floor(pixel.x/self.tilewidth) + 1
     local tile_y = math.floor(pixel.y/self.tileheight) + 1
     local value = self.data[tile_x + (tile_y - 1)*self.width]
     return Tile:new(tile_x, tile_y, self.tilewidth, self.tileheight, value)
  end

  return Map

Tile class

Tiles will be represented as very simple objects consisting of basic attributes such as:

• width and height
• tile-space position (not pixel)
• whether their solid or not

I'm making tiles be vectors in order to easily find adjacent tiles by adding or subtracting unit vectors.

  local Vector = require("vector")

  local Tile = Vector:extend()

The initializer is otherwise simple, storing the arguments and creating a pixel_rect table to easily map a tile to its pixels on the screen.

  function Tile:init(x, y, w, h, value)
  	 Tile.__super.init(self, x, y)
  	 self.w = w
  	 self.h = h
  	 self.pixel_rect = {
  		x=(x - 1)*self.w,
  		y=(y - 1)*self.h,
  		w=self.w,
  		h=self.h,
  	 }
  	 self.value = value
  	 self.solid = not (value == 0 or value == nil)
  end

  return Tile

Entity class

If my mind's bandwidth allows, I may also learn some ECS, so let's start with an entity class that has position and velocity (which should later become components?).

In any case, an entity will have these attributes:

pos

the x and y coordinates of the entity's center

vel

the entity's velocity vector

acc

the entity's acceleration vector

rect

the entity's bounding rect, with x and y for the top left corner, and w and h for its width and height, respectively

Also, I want to create an API to allow controlling any entity's actions, namely:

• walk
• jump
• attack
• draw

All of that while having gravity always affect an entity. I'm thinking of starting off with walking and jumping, for which an entity object would provide move and jump methods respectively. The move method in particular would take a movement object, which specifies in which direction it's moving (left or right) or jumping, which is basically the game's input object.

  local Object = require("object")
  local Vector = require("vector")
  local Tile = require("tile")
  local helpers = require("helpers")
  local inspect = require("inspect/inspect")

  local Entity = Object:extend()

  function Entity:init(x, y, w, h, gravity, max_jump_height, horizontal_acc, friction, map)
     Entity.__super.init(self, x, y, w, h)
     self.gravity = gravity
     self.pos = Vector:new(x, y)
     self.vel = Vector:new(0, 0)
     self.maxvel = Vector:new(8*8, 8*24)
     self.width = w
     self.height = h
     self.grounded = false
     self.horizontal_acc = horizontal_acc
     self.max_jump_height = max_jump_height
     self.friction = friction
     self.map = map
  end

  function Entity:get_rect()
     return {x=self.pos.x - self.width/2, y=self.pos.y - self.height/2, w=self.width, h=self.height}
  end

  function Entity:draw()
     local rect = self:get_rect()
     love.graphics.setColor(0, 0, 0.8)
     love.graphics.rectangle("fill", helpers.round(rect.x),	helpers.round(rect.y), rect.w, rect.h)
     love.graphics.setColor(1, 0, 0)
     love.graphics.circle("fill", self.pos.x, self.pos.y, 1)
  end

Each frame, we'll want to update an entity's state. This means updating its velocity and position based on its previous state, and then adjusting that next state if there are collisions that would prevent actually moving there.

The first step is to create a copy of the current state so we work on that rather than the actual entity, thus, let's define a copy method:

  function Entity:copy()
     local new = Entity:new(self.pos.x, self.pos.y, self.width, self.height, self.gravity, self.max_jump_height, self.horizontal_acc, self.friction, self.map)
     new.vel.x = self.vel.x
     new.vel.y = self.vel.y
     new.grounded = self.grounded
     return new
  end

Next, let's define the move method, which takes a movement object (basically, the player's input), and the time delta since the last frame, and will create a copy, update its velocity and position, check for collisions, and return a new entity with the updated state.

First, let's do the horizontal movement (walking or flying?)

  -- TODO: check if not grounded and allow air control
  function Entity:move_horizontally(movement, dt)
     local x_accel = 0
     local next_state = self:copy()
     if movement.right or movement.left then
  	  if movement.right then
  		 x_accel = self.horizontal_acc
  	  else
  		 x_accel = -self.horizontal_acc
  	  end
     else
  	  if self.vel.x < 0 then
  		 x_accel = self.friction
  	  elseif self.vel.x > 0 then
  		 x_accel = -self.friction
  	  end
     end
     next_state.vel.x = helpers.bound(self.vel.x + x_accel*dt, -self.maxvel.x, self.maxvel.x)
     next_state.pos.x = helpers.normalize(self.pos.x + next_state.vel.x*dt, self.width/2, self.map.max_pixel.x + self.width*1.5)

     if self.vel.x < 0 and next_state.vel.x > 0 or self.vel.x > 0 and next_state.vel.x < 0 then
  	  next_state.vel.x = 0
     end

     return next_state
  end

Next, let's handle jumps with a method that assumes the player is allowed to jump, i.e. is grounded.

  function Entity:jump(dt)
     local next_state = self:copy()
     next_state.grounded = false
     next_state.vel.y = -math.sqrt(2*self.max_jump_height*self.gravity)
     next_state.pos.y = helpers.bound(next_state.pos.y + next_state.vel.y*dt, 0, self.map.max_pixel.y - self.height/2)
     return next_state
  end

When the entity isn't grounded and isn't jumping, it's falling:

  function Entity:fall(dt)
     local next_state = self:copy()
     next_state.grounded = false
     next_state.vel.y = self.vel.y + self.gravity*dt
     next_state.pos.y = helpers.bound(next_state.pos.y + next_state.vel.y*dt, 0, self.map.max_pixel.y - self.height/2)
     return next_state
  end

Lastly, we also need a way to ground the entity, setting the grounded flag to true, and its vertical velocity to 0.

  function Entity:ground()
     local next_state = self:copy()
     next_state.grounded = true
     next_state.vel.y = 0
     return next_state
  end

We'll need to check for collisions against solid tiles and adjust the entities position:

  function Entity:adjust_for_collisions(old_state, dt, frame)
     local next_state = self:copy()
     local top_left_tile = self.map:get_tile_from_pixel({
  		 x=next_state.pos.x - next_state.width/2,
  		 y=next_state.pos.y - next_state.height/2,
     })
     local bottom_left_tile = self.map:get_tile_from_pixel({
  		 x=next_state.pos.x - next_state.width/2,
  		 y=next_state.pos.y + next_state.height/2,
     })
     local bottom_right_tile = self.map:get_tile_from_pixel({
  		 x=next_state.pos.x + next_state.width/2,
  		 y=next_state.pos.y + next_state.height/2,
     })
     local top_right_tile = self.map:get_tile_from_pixel({
  		 x=next_state.pos.x + next_state.width/2,
  		 y=next_state.pos.y - next_state.height/2,
     })

     local next_rect = next_state:get_rect()

     if old_state.grounded and self.vel.y >= 0 then
  	  if
  		 self.vel.x < 0 and not bottom_left_tile.solid
  		 or self.vel.x > 0 and not bottom_right_tile.solid
  	  then
  		 next_state = next_state:fall(dt)
  	  end
     end
     if not self.grounded then
  	  if self.vel.y < 0 and (
  		 top_left_tile.solid and helpers.rectangles_overlap(next_rect, top_left_tile.pixel_rect)[2]
  		 or
  		 top_right_tile.solid and helpers.rectangles_overlap(next_rect, top_right_tile.pixel_rect)[2]
  	  ) then
  		 next_state.pos.y = top_right_tile.y + top_right_tile.h - self.height/2
  		 next_state.vel.y = 0
  		 print(frame, "CEILING BUMP!")
  	  elseif self.vel.y >= 0 and (
  		 bottom_left_tile.solid and helpers.rectangles_overlap(next_rect, bottom_left_tile.pixel_rect)[3]
  		 or
  		 bottom_right_tile.solid and helpers.rectangles_overlap(next_rect, bottom_right_tile.pixel_rect)[3]
  	  ) then
  		 next_state = next_state:ground()
  		 print(frame, "GROUNDED BECAUSE OF LANDING")
  		 next_state.pos.y = bottom_right_tile.pixel_rect.y - self.height/2
  	  end
     end

     if old_state.vel.x < 0 then
  	  if top_left_tile.solid and helpers.rectangles_overlap(next_rect, top_left_tile.pixel_rect)[2] then
  		 next_state.vel.x = 0
  		 next_state.pos.x = top_left_tile.pixel_rect.x + top_left_tile.pixel_rect.w + next_rect.w/2
  	  end
     elseif old_state.vel.x > 0 then
  	  if top_right_tile.solid and helpers.rectangles_overlap(next_rect, top_right_tile.pixel_rect)[2] then
  		 next_state.vel.x = 0
  		 next_state.pos.x = top_right_tile.pixel_rect.x - next_rect.w/2
  	  end
     end

     if next_state.grounded and next_state.vel.y ~= 0 then
  	  print(frame, "GROUNDED WITH VERTICAL VELOCITY", next_state.vel.y, "THIS SHOULD NOT HAPPEN")
  	  next_state.vel.y = 0
     end

     return next_state
  end

  function Entity:move(movement, dt, frame)
     local wasright = self.vel.x > 0
     local wasleft = self.vel.x < 0
     local justjumped = false
     local accel = Vector:new(0, self.gravity)

     local next_state = self:move_horizontally(movement, dt)

     if self.grounded then
  	  if movement.jump then
  		 next_state = next_state:jump(dt)
  	  end
     else
  	  next_state = next_state:fall(dt)
     end

     if not (next_state.pos == self.pos) then
  	  if distance(self.pos, next_state.pos) > 8 then
  		 print(frame, "ENTITY MOVING TOO FAST!", inspect(self.pos), inspect(next_state.pos))
  		 -- swept AABB
  	  else
  		 next_state = next_state:adjust_for_collisions(self, dt, frame)
  	  end
     end
     return next_state
  end
  return Entity

  local Entity = require("entity")

Enemy class

Now that we have the Entity class, let's extend it for enemies. Initially this will only override the draw method to use a different color, but later we'll add more specific behavior (as well as different sprites) and maybe even more subclasses for each enemy type.

  local helpers = require("helpers")
  local Entity = require("entity")

  local Enemy = Entity:extend()

  function Enemy:draw()
     self.__super.draw(self)
     local rect = self:get_rect()
     love.graphics.setColor(0.9, 0, 0.2)
     love.graphics.rectangle("fill", helpers.round(rect.x), helpers.round(rect.y), rect.w, rect.h)
  end

  return Enemy

Initialization

Next, we define love.load(), which should take care of:

• loading graphics, setting the scale
• setting up animations
• loading the level and mapping it into data in the game object.

• initialize the player and other objects

  • this will be moved to a level initialization function later on

I want a retro look, so pixels should look sharp, I could use a library like maid64, but I'll just keep things simple by:

• setting the nearest neighbor interpolation as the default scaling filter
• calculate the scaling factors for width and height, which will be used when drawing stuff

  local screen_width = 320 --self.map.width*self.map.tilewidth
  local screen_height = 200 -- self.map.height*self.map.tileheight
  love.graphics.setDefaultFilter("nearest", "nearest")
  local desktop_width, desktop_height = love.window.getDesktopDimensions()
  scale_width = desktop_width/screen_width
  scale_height = desktop_height/screen_height

Next, all we need to do is create the first game state players will see, which is the title screen. All the logic for switching to other states is self-contained:

  current_state = states.Title:new()

Putting it all together in LÖVE's load callback:

    local scale_width, scale_height, current_state
       function love.load()
          <<initGraphics>>
          <<initGameState>>
       end

Game logic

Flicky's gameplay seems basic at first, but there's quite a bit of stuff going on:

controls

move left and right, jump

objective

collect "Chirps" and take them to the exit

• Chirps will follow Flicky around until then

enemies

cats move around the level (there's other types of enemies in later levels)

• if they touch Flicky, a life is lost
• if they touch a Chirp, it stops following Flicky
• enemies respawn from fixed points
• enemies can be taken down if Flicky kicks throwable items like flower pots at them

?

levels wrap around, giving the illusion of a bigger, infinite level

This means the game logic should keep track of a few things:

• Flicky's state

  • position
  • probably other physics stuff too, like velocity, etc.
  • lives
  • whether Flicky is carrying an item or not (maybe just an item attribute that can be nil)
• Camera's position, based on Flick's position

• Chirps' position, and whether they're following Flicky

  • I'm thinking Chirps could be small state machines

• Level-specific stuff

  • Initial enemies position
  • Enemy spawner positions
  • How many enemies are active
  • Maximum allowed enemies
• Platforms

• Game state stuff

  • Collected chirps count
  • Timer

At the most basic (i.e. the whole game being a single level) that results in a few main functions love.update(dt) will call:

Updating each frame

At the highest level, updating each frame is pretty simple:

• update the current game state
• check if the current state has ended
• if it has, switch to its next state

  function love.update(dt)
     current_state:update(dt)
     if current_state.ended then
  	  current_state = current_state.next
     end
  end

Drawing to the screen

First up, let's reset the color every time we draw so it doesn't tint everything with the color that was used last:

  love.graphics.setColor(1, 1, 1)

Go through each tile in the map and query its value to draw solid tiles (value > 0) in color (this will later be replaced by drawing the actual tile graphics form the tilesheet.) We'll also do scaling using the calculated scale factors from the game object: game:draw_debug_infos()

#+end_src

  function love.draw()
  		<<resetColor>>
  		love.graphics.push()
  		love.graphics.scale(scale_width, scale_height)
  		current_state:draw()
  		love.graphics.pop()
  end

Ideas

I'm thinking once I have the core of the game working I can try introducing some throwing mechanics like Yoshi's Story. Either throw the chicks/eggs themselves, or have some special pickup that can be thrown at enemies.

Devlog

[2024-08-17 sáb]

Not a huge amount of work this week, but feeling good about it, noteworthy stuff so far:

• broke up entity movement and collision detection into separate methods
• jumping feels nice, and got the code layed out so I can set whatever max height I want
• collision with tiles still not perfect, but we're getting there

Next week I want to work on:

• game states (at least get a menu/title screen)
• add other entities to the game with stupid AI
• stretch: some pixel art

[2024-09-02 lun]

I was able to work on game states but got detoured with making a Map class that would allow iterating over instances of it returning each tile that makes up the map, and got into a Lua iterators rabbit hole which ended up finding out __ipairs is no longer supported (for quite a while), so I had to just make a plain iterator method (that led me to think a lot about my choosing Lua for this.) In any case, I'm glad I was able to stub out the title screen along with the game states architecture.

The game is currently not working, but this is what I did this week:

• GameState class
• Move gameplay code into Play GameState subclass
• Implement Title GameState subclass, working with input to switch to Play state
• Clean up a bunch of old code
• Map class to encapsulate tile logic, with iterator yielding Tile instances
• Got working title idea: "Michi Dragon"
• Started stubbing out title screen art

This week I'd like to:

• get game working again (fix map/tiles code)
• work on simple title screen art
• update literary parts for all the code I added last week

[2024-09-24 mar]

Hadn't realized it's been such a while since I added a devlog, I'll start making specific commits for these. I actually got a good rhythm going on now that some of the big ground-level stuff is working somewhat decently. These are the latest updates:

• Game is working again!
• Game states themselves work nicely, there's a simple title screen from which the main play state can be accessed
• Updated and added a bunch of "literary" parts
• Added missing files to git
• Entities no longer endlessly bump with tiles when moving horizontally
• Started off with an Enemy class and added a few "enemies" moving around

Next up I'd love to work on these:

• collisions between entities (enemy/player)
• game over state
• pause (sub)state
• some pixel art for heck's sake

Plan

TODO Install dependencies (inspect, debugger) through luarocks

DONE Create object base "class" with copy metamethods functionality, explain literarily

DONE Refactor Object:new, Object:init, introduce Object:extend

TODO Convert acceleration to vector in Entity:move

DONE Fix gravity always changing position in y axis on Entity:move   bug

SCHEDULED: <2024-08-08 jue 14:00-15:00> DEADLINE: <2024-08-09 Fri>

CLOCK: [2024-08-07 mié 11:42]–[2024-08-07 mié 12:11] => 0:29

DONE Add grounded attribute to player/entity

DONE love.load()

DONE [A] Bugfix drawing offset by 1 in x and y

DONE love.update(dt)

DONE love.draw()

Explain game.map:box2d_draw call for debugging purposes.

DONE Level wrap-around

DONE Bugfix level wrap-around

Can't move past right side of the level, but going to the left works (?)

DONE Update "literary" parts

DEADLINE: <2024-09-11 mié>

CLOCK: [2024-09-10 mar 07:08]–[2024-09-10 mar 07:45] => 0:37

TODO Player slide

Tweak friction values

TODO changing direction while in mid air should have lots of friction

TODO Bugfix Enemy:draw not working

DEADLINE: <2024-09-30 Mon>

I think the problem is actually with Enemy:move returning entities instead of enemy objects.

DONE Refactor player, enemies, items code into entities

DONE Add a couple enemy entities with stupid AI

DEADLINE: <2024-09-23 Mon>

CLOCK: [2024-09-24 mar 08:12]–[2024-09-24 mar 08:51] => 0:39

maybe they just move left or right constantly, jump if they "see" a gap or blocking tile ahead.

TODO Title screen art mock

DEADLINE: <2024-09-27 Fri>

CLOCK: [2024-09-04 mié 11:45]–[2024-09-04 mié 12:08] => 0:23 CLOCK: [2024-08-20 mar 11:39]–[2024-08-20 mar 12:06] => 0:27

fonts I like:

• Essays
• dhurjati (maybe for a shmup)
• lmmono10-italic
• lmromanusl10-regular
• lmu10
• qzcmi
• texgyrechorus-med

TODO Gameplay screen art mock

DEADLINE: <2024-10-02 mié>

DONE Fix Tile class ipairs

SCHEDULED: <2024-08-29 jue 10:30-11:30> DEADLINE: <2024-08-30 Fri>

CLOCK: [2024-08-29 jue 10:42]–[2024-08-29 jue 11:14] => 0:32

Turns out Lua no longer supports the __ipairs metamethod (hasn't for years), bummer.

DONE Collision with platforms above when jumping

TODO Camera fixed on player position

Bonus points for a small offset left and right before moving camera position.

DONE Implement game states

DEADLINE: <2024-08-30 Fri>

CLOCK: [2024-08-21 mié 07:26]–[2024-08-21 mié 07:57] => 0:31

• Title/Menu
• Gameplay
• Game Over
• Finished game

TODO Explain game object components

TODO Refine player movement

TODO Bugfix scaling and/or drawing

DONE Maybe create a game class, player class, etc.

TODO Explain 320x200 resolution

TODO Fix aspect ratio

Using 16:10, should add "black bars" on the sides (or on top and bottom)

But how?

DONE Bugfix jump code

Jumping is somewhat inconsistent, if you hold jump, final jump height varies quite a bit.

Got this one fixed by setting a fixed Y velocity when jump button is hit, rather than calculating a new acceleration with dt. (Should explain this in the literate part)

TODO Set up some kind of debug mode (toggle?)

TODO Define enemy spawner logic (a few different options)

DONE Map player position correctly when drawing

TODO Create lower-resolution internal game model

DONE Consider dropping game.world and not using STI's box2d support

I'm following Code inComplete's Tiny Platformer article, coding the physics from scratch somewhat. Maybe start off like that and later try to refactor into LOVE's physics?

Draw debug helpers

• draw player's "tile"

DONE Draw platforms from game.platforms table

TODO slide animation when direction button is released

TODO Generic Object:copy method

TODO Decouple GameState objects, map (maybe), and graphics

DONE Fix collision with solid tile when moving horizontally

SCHEDULED: <2024-09-19 jue 15:45-16:30> DEADLINE: <2024-09-21 sáb>

CLOCK: [2024-09-19 jue 19:04]–[2024-09-19 jue 19:24] => 0:20 CLOCK: [2024-09-19 jue 08:12]–[2024-09-19 jue 08:58] => 0:46 CLOCK: [2024-08-13 mar 12:01]–[2024-08-13 mar 12:13] => 0:12

289 DETECTED COLLISION WHEN MOVING LEFT TOWARDS 200 NEXT X: 199.17442941018 CURRENT VEL.X -64 NEXT RECT { h = 8, w = 4, x = 197.17442941018, y = 184 } TILE RECT { h = 8, w = 8, x = 192, y = 184 }

Seems it's detecting the wrong tile in the next frame after a collision detection? Need to check next_state.pos and resulting top_left_tile for this case.

289 ADJUSTED X 202 291 NO COLLISION WHEN MOVING LEFT TOWARDS 208 NEXT X: 201.85257872008 CURRENT VEL.X -1.7781952 NEXT RECT { h = 8, w = 4, x = 199.85257872008, y = 184 }

TODO Implement game pause as Play substate

DEADLINE: <2024-09-24 Tue>

TODO replace hardcoded player initial position (180, 100) with marker/point from Tiled map

TODO Reimplement draw_debug_infos

DEADLINE: <2024-09-20 Fri>

Need something more global, maybe that takes a game state instance or something.

DONE Fix jump

SCHEDULED: <2024-08-13 mar 11:15-12:00>

TODO Bugfix ceiling bump teleport

DEADLINE: <2024-10-07 Mon>

TODO Try implementing wrap-around with polar coordinates and cosine

DEADLINE: <2024-10-02 mié>

    -- Constants
    local radius = 100  -- Radius of the "circle" that represents the screen width
    local max_velocity = 4 * math.pi  -- Max angular velocity (2 full circle per second)
    local acceleration = 0.2  -- Angular acceleration

    -- Initial state
    local theta = 0  -- Initial angle (in radians)
    local angular_velocity = 0  -- Initial angular velocity
    local delta_time = 1/30  -- Time step (e.g., 1/30th of a second)

    -- Function to update the entity's position
    function update_position()
  	 -- Apply angular acceleration
  	 angular_velocity = angular_velocity + acceleration * delta_time

  	 -- Cap the angular velocity at max_velocity
  	 if angular_velocity > max_velocity then
          angular_velocity = max_velocity
  	 end

  	 -- Update the angle (theta)
  	 theta = theta + angular_velocity * delta_time

  	 -- Ensure theta stays within [0, 2 * pi] to simulate wrap-around
  	 if theta >= 2 * math.pi then
          theta = theta - 2 * math.pi
  	 elseif theta < 0 then
          theta = theta + 2 * math.pi
  	 end

  	 -- Calculate the horizontal position using the cosine of the angle
  	 local x_position = radius * math.cos(theta)

  	 return x_position
    end

    -- Example usage
    for i = 1, 60 do
  	 local x = update_position()
  	 print(string.format("Time: %.2f, X Position: %.2f", i * delta_time, x))
    end