Performance of generating 5 242 880 numbers

[mihaly-sisak]

Hello everybody!

I plan on implementing add-on support for my pet project, and so far Luau looks like the most battle tested solution! I love the sandboxing and the type checking features!

One of my use-cases would be world generation. I threw together an example script to see what I can do.

local function perlin2d(edge_size: number): {[number]: number}
    
    print("Generating 2D perlin noise array...")

    local time_start = os.clock()

    local cell_size = 5
    local count     = edge_size * edge_size * cell_size
    local numbers   = table.create(count)

    for x = 0, edge_size-1 do
        for y = 0, edge_size-1 do
            local i = (x * edge_size + y) * cell_size
            numbers[i+1] = math.noise(x+0.50, y+0.50)
            numbers[i+2] = math.noise(x+0.25, y+0.25)
            numbers[i+3] = math.noise(x+0.25, y+0.75)
            numbers[i+4] = math.noise(x+0.75, y+0.25)
            numbers[i+5] = math.noise(x+0.75, y+0.75)
        end
    end

    local time_end = os.clock()

    print("Generated " .. #numbers .. " numbers, took " .. (time_end - time_start) .. " seconds")

    return numbers
end

perlin2d(2^10) -- 1024

Please be gentle, this is my first lua code ever. I plan to sample a 2d perlin noise, then filter the results and generate a world based on that.

My problem is that this takes 0.6 seconds to run. (The same thing is cpp takes 0.19) I tried profiling:

Sadly this gives me no pointer where the bottleneck is. Is this lua code sane? I find it difficult to find resources for lua, is there some golden tutorial for luau, on how to write performant lua code?

[mihaly-sisak]

I managed to get a primitive array type working:

local function test_array2(edge_size)
    print("Generating 2D perlin noise array...")
    local time_start = os.clock()

    local cell_size = 5

    local x = array.new({edge_size, edge_size, cell_size}, 1)
    local y = array.new({edge_size, edge_size, cell_size}, 2)
    local n = array.noise(x, y)

    local time_end = os.clock()
    print("Generated " .. #n .. " numbers, took " .. (time_end - time_start) .. " seconds")
end

This is not 100% the same as the first version (missing the 0.25, 0.5, 0.75 offsets), more like a prototype ndarray implementation. It takes 0.26 seconds, according to perf mainly because it has to malloc 3 times, instead of once. I copied the perlin algo from luau/VM/src/lmathlib.cpp.

Is there a numpy-like library I can use with Luau? I can implement the methods more or less but I feel like I would duplicate work and my version would be sub standard.

[mihaly-sisak]

https://github.com/mihaly-sisak/luau_torch7
Turns out PyTorch was simply Torch before, used with Lua. It has everything I need, arithmetic, filtering of big tensors. Sadly it hardly works with Luau. I got it barely-running after tinkering for a few days, is there a market need for this or am I alone?

[mihaly-sisak]

I polished it up, added back a lot of features that first did not work