Love Game Engine

--[[

engine.lua
Version: 1.2

Author: MegaLoler
Email: megaloler9000@gmail.com

A game engine for Love that manages game scenes and entities.

If requires that you use the class.lua file:
require("class.lua")

Make sure you have this in your code:
require("engine.lua")

Create a game by creating a subclass of the Engine class.
MyGame = engine.newClass(engine.Engine)

Define the setup method:
function MyGame:setup()
    -- Initalize your game here.
end

Make sure to call the setGame function of your game class in your main.lua:
MyGame:setGame()  -- This will make the game engine take over.

Create a scene by subclassing the Entity class:
TestScene = newClass(engine.Entity)

Define the setup, update, draw, and any other methods that you wish:
function TestScene:setup() ... end
function TestScene:update(dt) ... end
function TestScene:draw() ... end

Call the setScene method somewhere in your game's setup method to set the inital scene on launch:
self:setScene(TestScene) -- Pass the class itself, not an instance of it

Add children entities to a scene or entity preferably in its setup method with the addChild method:
local child = TestEntity:new(self.engine, self) -- Parameters are game engine and parent entity
self:addChild(child)

--]]

require("class")

engine = {} -- Engine package

-- Love wrappers

function love.load()
    engine.game:load()
end

function love.quit()
    engine.game:quit()
end

function love.focus(f)
    engine.game:focus(f)
end

function love.keypressed(key, unicode)
    engine.game:keypressed(key, unicode)
end

function love.keyreleased(key)
    engine.game:keyreleased(key)
end

function love.mousepressed(x, y, button)
    engine.game:mousepressed(x, y, button)
end

function love.mousereleased(x, y, button)
    engine.game:mousereleased(x, y, button)
end

function love.update(dt)
    engine.game:update(dt)
end

function love.draw()
    engine.game:draw()
end

-- Engine class

engine.Engine = newClass()

function engine.Engine:init()
    self:setSize()
    self:setTitle()
    self.focused = true
    self.fading = false
    self.fade = 1
    self.fadeSpeed = 0.5
    self.fadeColor = {255, 255, 255}
    self:setScene(engine.Entity)
end

-- Sets the engine subclass to load

function engine.Engine:setGame()
    engine.game = self:new()
end

-- Engine methods

function engine.Engine:setTitle(title)
    self.title = title or "Game Engine"
    love.graphics.setCaption(self.title)
end

function engine.Engine:setSize(width, height)
    self.width = width or 640
    self.height = height or 480
    love.graphics.setMode(self.width, self.height)
    if self.scene then self:positionScene() end
end

function engine.Engine:fadeToScene(scene, ...)
    self.fadeTo = scene
    self.fadeArgs = ...
    self.fading = true
end

function engine.Engine:setScene(scene, ...)
    if self.scene then self.scene:destroy() end
    self.scene = scene:new(self)
    self:positionScene()
    self.scene:setup(...)
end

function engine.Engine:toggleFullscreen()
    love.graphics.toggleFullscreen()
end

-- Wrapped Love functions

function engine.Engine:load()
    self:setup()
end

function engine.Engine:quit()
end

function engine.Engine:focus(f)
    self.focused = f
end

function engine.Engine:keypressed(key, unicode)
    self.scene:onkeypressed(key, unicode)
end

function engine.Engine:keyreleased(key)
    self.scene:onkeyreleased(key)
end

function engine.Engine:mousepressed(x, y, button)
    self.scene:onmousepressed(x, y, button)
end

function engine.Engine:mousereleased(x, y, button)
    self.scene:onmousereleased(x, y, button)
end

function engine.Engine:update(dt)
    if self.fading then
        if self.fade >= 1 then
            self.fade = 1
            self.fading = false
            self:setScene(self.fadeTo, self.fadeArgs)
        else
            self.fade = self.fade + self.fadeSpeed * dt
            if self.fade > 1 then self.fade = 1 end
        end
    else
        if self.fade <= 0 then
            self.fade = 0
        else
            self.fade = self.fade - self.fadeSpeed * dt
            if self.fade < 0 then self.fade = 0 end
        end
    end
    self.scene:masterUpdate(dt)
end

function engine.Engine:draw()
    self.scene:render()
    love.graphics.setCanvas()
    self.scene:postRender()
    self:drawFade()
end

-- Private methods

function engine.Engine:positionScene()
    self.scene:setPosition(self.width / 2, self.height / 2)
end

function engine.Engine:drawFade()
    love.graphics.setBlendMode("alpha")
    love.graphics.setColor(self.fadeColor[1], self.fadeColor[2], self.fadeColor[3], (math.cos((1 - self.fade) * math.pi) + 1) * 127)
    love.graphics.polygon("fill", 0, 0, self.width, 0, self.width, self.height, 0, self.height)
end

-- Virtual methods

function engine.Engine:setup()
end

-- Entity class

engine.Entity = newClass()

function engine.Entity:init(engine, container)
    self.engine = engine
    self.container = container
    self:setSize()
    self:setPosition()
    self:setOrientation()
    self:setScale()
    self:setColor()
    self.backgroundAlpha = 255
    self.alpha = 255
    self:setBackgroundColor()
    self.children = {}
    self.selectable = false
    self.selected = false
    self.clearCanvas = true
    self.hasBackground = false
    self.staticDrawing = true
    self.refreshRequested = true
end

-- Entity methods

function engine.Entity:addChild(child, ...)
    table.insert(self.children, child)
    child:setup(...)
end

function engine.Entity:removeChild(child)
    table.remove(self.children, child)
    child:destroy()
end

function engine.Entity:refresh()
    self.refreshRequested = true
end

function engine.Entity:setColor(color)
    self.color = color or {255, 255, 255}
end

function engine.Entity:setBackgroundColor(color)
    local r, g, b = love.graphics.getBackgroundColor()
    self.backgroundColor = color or {r, g, b}
end

function engine.Entity:setPosition(x, y)
    local dx = self.engine.width / 2
    local dy = self.engine.height / 2
    if self.container then
        dx = self.container.width / 2
        dy = self.container.height / 2
    end
    self.x = x or dx
    self.y = y or dy
end

function engine.Entity:move(x, y)
    self.x = self.x + x
    self.y = self.y + y
end

function engine.Entity:setOrientation(r)
    self.orientation = r or 0
end

function engine.Entity:setScale(x, y)
    self.scaleX = x or 1
    self.scaleY = y or 1
end

function engine.Entity:setSize(width, height)
    self.width = width or self.engine.width
    self.height = height or self.engine.height
    self.canvas = love.graphics.newCanvas(self.width, self.height)
end

function engine.Entity:masterUpdate(dt)
    for k, v in pairs(self.children) do
        v:masterUpdate(dt)
    end
    self:update(dt)
end

function engine.Entity:render()
    if not self.staticDrawing or self.refreshRequested then
        self.refreshRequested = false
        love.graphics.setCanvas(self.canvas)
        if self.clearCanvas then self.canvas:clear() end
        if self.hasBackground then
            love.graphics.setColor(self.backgroundColor[1], self.backgroundColor[2], self.backgroundColor[3], self.backgroundAlpha)
            love.graphics.setBlendMode("alpha")
            love.graphics.polygon("fill", 0, 0, self.width, 0, self.width, self.height, 0, self.height)
        end

        self:preDraw()

        for k, v in pairs(self.children) do
            v:render()
            love.graphics.setCanvas(self.canvas)
            v:postRender()
        end

        self:draw()
    end
end

function engine.Entity:postRender()
    love.graphics.setBlendMode("alpha")
    love.graphics.setColor(self.color[1], self.color[2], self.color[3], self.alpha)
    love.graphics.drawq(self.canvas, love.graphics.newQuad(0, 0, self.width, self.height, self.width, self.height), self.x, self.y , self.orientation, self.scaleX, self.scaleY, self.width / 2, self.height / 2)
end

function engine.Entity:onkeypressed(key, unicode)
    self:keypressed(key, unicode)
    if self.selectedChild then self.selectedChild:onkeypressed(key, unicode) end
end

function engine.Entity:onkeyreleased(key)
    self:keyreleased(key)
    if self.selectedChild then self.selectedChild:onkeyreleased(key) end
end

function engine.Entity:onmousepressed(x, y, button)
    local oldSelectedChild = self.selectedChild
    self:mousepressed(x, y, button)
    if self.selectedChild then self.selectedChild.selected = false end
    self.selectedChild = self:getChildAtLocation(x, y)
    if self.selectedChild and not self.selectedChild.selectable then self.selectedChild = nil end
    if self.selectedChild then
        self.selectedChild.selected = true
        x, y = self:localCoordsToChildCoords(x, y, self.selectedChild)
        self.selectedChild:onmousepressed(x, y, button)
    end
    if self.selectedChild ~= oldSelectedChild then
        if oldSelectedChild then oldSelectedChild:focus(false) end
        if self.selectedChild then self.selectedChild:focus(true) end
    end
end

function engine.Entity:onmousereleased(x, y, button)
    self:mousereleased(x, y, button)
    if self.selectedChild then
        x, y = self:localCoordsToChildCoords(x, y, self.selectedChild)
        self.selectedChild:onmousereleased(x, y, button)
        if self.selectedChild:inBounds(x, y) then self.selectedChild:mouseclicked(x, y, button) end
    end
end

-- Private methods

function engine.Entity:inBounds(x, y)
    return x >= 0 and x < self.width and y >= 0 and y < self.height
end

function engine.Entity:getChildAtLocation(x, y)
    for i = 1, #self.children do
        local child = self.children[#self.children - (i - 1)]
        local cx, cy = self:localCoordsToChildCoords(x, y, child)
        if child:inBounds(cx, cy) then return child end
    end
end

function engine.Entity:localCoordsToChildCoords(x, y, child)
    x = (x - child.x) / child.scaleX
    y = (y - child.y) / child.scaleY

    distance = math.sqrt((x * x) + (y * y))
    angle = math.atan2(y, x) - child.orientation

    x = math.cos(angle) * distance
    y = math.sin(angle) * distance

    x = x + child.width / 2
    y = y + child.height / 2

    return x, y
end

-- Virtual methods

function engine.Entity:setup(...)
end

function engine.Entity:destroy()
end

function engine.Entity:focus(f)
end

function engine.Entity:keypressed(key, unicode)
end

function engine.Entity:keyreleased(key)
end

function engine.Entity:mousepressed(x, y, button)
end

function engine.Entity:mousereleased(x, y, button)
end

function engine.Entity:mouseclicked(x, y, button)
end

function engine.Entity:update(dt)
end

function engine.Entity:preDraw()
end

function engine.Entity:draw()
end