3D Cube

-- This program was made while following this video about programming in Apple II BASIC:
-- https://www.youtube.com/watch?v=PHfKCxjsmos
-- This program renders a 3D cube being rotating along x, y, and z axes at 60fps.
-- This code will only work in ComputerCraft.
local round = function(n)
    return math.floor(n+0.5)
end

local wait = (function()
    local ticks = 0
    local startTime = os.clock()
    local frames = {os.clock()}
    local fps = 0

    return setmetatable({
        ticks = function() return ticks end,
        frameTime = function(real)
            local time = os.clock()-frames[1]
            if real then return time / fps
            else return round(time / fps * 20) / 20 end
        end,
        startTime = function() return startTime end,
        programClock = function() return os.clock() - startTime end,
        fps = function() return fps end
    }, {
        __call = function(self, n)
            n = tonumber(n) or 20
            if n <= 0 then error("Value out of range, must be greater than 0", 2) end
            ticks = ticks + 1
            frames[#frames+1] = os.clock()
            if n <= 20 then
                sleep(1/n)
            elseif ticks%round(n/20) == 0 then
                sleep(0.05)
            end
            while os.clock()-frames[1] > 1 and #frames > 1 do
                table.remove(frames, 1)
            end
            fps =  #frames / (os.clock() - frames[1]) - (math.floor(n/20)-1)
            return fps
        end
    })
end)()

local xSize, ySize = term.getSize()
local winBuffer = {
    [1] = window.create(term.current(), 1, 1, xSize, ySize),
    [2] = window.create(term.current(), 1, 1, xSize, ySize)
}
local cubeSize = ySize*1.4
local xCenter, yCenter = round(xSize/2), round(ySize/2)
local win = 1
local angle = 0
local points = {}

for n = 1, 8 do
    local x, y, z = 0, 0, 0
    if n%4 < 2 then x = -1 else x = 1 end
    if (n-1)%4 < 2 then y = -1 else y = 1 end
    if n < 5 then z = -1 else z = 1 end
    points[n] = {
        position = vector.new(x, y, z),
        rotation = {
            x = vector.new(0, 0, 0),
            y = vector.new(0, 0, 0),
            z = vector.new(0, 0, 0)
        },
        projection = vector.new(0, 0, 0)
    }
end

local drawLine = function(a, b)
    local x1 = points[a].projection.x * cubeSize + xCenter
    local y1 = points[a].projection.y * cubeSize + yCenter
    local x2 = points[b].projection.x * cubeSize + xCenter
    local y2 = points[b].projection.y * cubeSize + yCenter
    paintutils.drawLine(x1, y1, x2, y2, colors.lime)
end

local bufferSwap = function()
    winBuffer[win].setVisible(true)
    if win == 1 then win = 2 else win = 1 end
    winBuffer[win].setVisible(false)
    term.redirect(winBuffer[win])
end

local setRotation = function()
    local cs = math.cos(angle)
    local sn = math.sin(angle)
    for n = 1, 8 do
        points[n].rotation.z.x = -cs*points[n].position.x + sn*points[n].position.y
        points[n].rotation.z.y = sn*points[n].position.x + cs*points[n].position.y
        points[n].rotation.z.z = points[n].position.z

        points[n].rotation.y.x = cs*points[n].rotation.z.x + sn*points[n].rotation.z.z
        points[n].rotation.y.y = points[n].rotation.z.y
        points[n].rotation.y.z = -sn*points[n].rotation.z.x + cs*points[n].rotation.z.z

        points[n].rotation.x.x = points[n].rotation.y.x
        points[n].rotation.x.y = cs*points[n].rotation.y.y - sn*points[n].rotation.y.z
        points[n].rotation.x.z = sn*points[n].rotation.y.y + cs*points[n].rotation.y.z

        local z = 1 / (5 - points[n].rotation.x.z)
        points[n].projection.x = points[n].rotation.x.x * z
        points[n].projection.y = points[n].rotation.x.y * z
    end
end

local drawCube = function()
    for n = 1, 8 do
        if n%4 > 0 then drawLine(n, n+1)
        else drawLine(n, n-3) end
        if n < 5 then drawLine(n, n+4) end
    end
end

while true do
    term.setBackgroundColor(colors.black)
    term.clear()
    term.setCursorPos(1, 1)
    print("FPS: " .. wait.fps())
    print("Start Time: " .. wait.startTime())
    print("Time Since Start: " .. wait.programClock())
    print("Ticks: " .. wait.ticks())
    print("Frametime: " .. wait.frameTime())
    print("Real Frametime: " .. wait.frameTime(true))
    print()
    print("Cube Size: " .. cubeSize)
    print("Angle: " .. round(angle*1000+500)/1000)
    setRotation()
    drawCube()
    angle = angle + 0.005
    bufferSwap()
    wait(60)
end