Pixel clone of Flappy bird using Love2d

main.lua

function love.load()
    reset()
    topscore = 0
    local font = love.graphics.newFont(24)
    love.graphics.setFont(font)
end

function reset()
    x = 60
    y = love.window.getHeight()/2
    vely = 0
    gravity = 0.5
    time = 0
    elapsed = 0
    enemies = {}
end

function wall_top(walltop)
    return {walltop[1], 0, 20, walltop[2]}
end

function wall_bot(wallbot)
    return {wallbot[1], wallbot[2], 20, love.window.getHeight()}
end

function collides(a, b)
      local t1 = {a[1], a[1] + a[3], a[2], a[2] + a[4]}
      local t2 = {b[1], b[1] + b[3], b[2], b[2] + b[4]}
      return not (t2[1] > t1[2] or
                  t2[2] < t1[1] or
                  t2[3] > t1[4] or
                  t2[4] < t1[3])

end

function love.draw()
    love.graphics.setColor(0,100,0,255)
    for i, enemy in pairs(enemies) do
        love.graphics.rectangle("fill", unpack(enemy))
    end

    love.graphics.setColor(255,0,0,255)
    love.graphics.rectangle("fill", x, y, 20, 20)

    love.graphics.setColor(255, 255, 255, 255)
    love.graphics.print("S: " .. math.floor(time), 10, 10)
    love.graphics.print("H: " .. topscore, 10, 40)
end

function love.update(dt)
    time = time + dt
    elapsed = elapsed + dt


    vely = vely + gravity
    y = y + vely

    if y > love.window.getHeight()-20 then
        y = love.window.getHeight() -20
    elseif y < 0 then
        y = 0
    end

    -- enemies
    if elapsed > 1 then
        local top = math.random(love.window.getHeight()/2)
        local bot = top+150
        table.insert(enemies, wall_top({love.window.getWidth(), top}))
        table.insert(enemies, wall_bot({love.window.getWidth(), bot}))
        elapsed = 0
    end

    for i, enemy in pairs(enemies) do
        enemy[1] = enemy[1] - 2

        if collides({x,y,20,20}, enemy) then
            topscore = math.max(topscore, math.floor(time))
            reset()
        end
    end
end

function love.keypressed(key)
    if key == '-' then
        love.window.setFullscreen(
            not love.window.getFullscreen())
    elseif key == 'escape' then
        love.quit()
    elseif key == ' ' then
        vely = -9
    end
end