## Mini Functions Repository

General discussion about LÖVE, Lua, game development, puns, and unicorns.
ZBoyer1000
Prole
Posts: 39
Joined: Sat Nov 28, 2015 10:13 am

### Mini Functions Repository

I thought it would be neat to create a place where people could post small functions that can do useful things and possibly help other people's projects. Here is a function I created that could help create game clocks:

Code: Select all

 gameClocks = {}
function clock(name, time)
index = 0
for i = 1,#gameClocks do
if gameClocks[i] == tostring(name) then
index = i
end
end
if index == 0 then
local clock = {tostring(name), num = 0}
table.insert(gameClocks, clock)
elseif index ~= 0 then
gameClocks[index].num = gameClocks[index].num + 1
if gameClocks[index].num >= time then gameClocks[index].num = 0 return true end
end
end

Here is an example for it: l = 0
z = 0
function love.update(dt)
if clock("LClock", 20) == true then
l = l + 1
end
if clock("ZClock", 1) == true then
z = z + 1
end
love.graphics.print(tostring(z) .. " : " .. tostring(l))
end
Last edited by ZBoyer1000 on Sat Apr 16, 2016 5:46 pm, edited 1 time in total.

Sulunia
Party member
Posts: 201
Joined: Tue Mar 22, 2016 1:10 pm
Location: SRS, Brazil

### Re: Mini Functions Repository

Welp, gonna contribute here.
Lerp funtion

Code: Select all

function lerp(a, b, rate) --EMPLOYEE OF THE MONTH
local result = (1-rate)*a + rate*b
return result
end
Usage:
speed = 0.05
myVar = lerp(myVar, newValue, speed)

Clamp function

Code: Select all

function clamp(number, maxvalue, minvalue)
if number > maxvalue then
number = maxvalue
elseif number < minvalue then
number = minvalue
end
return number
end

Usage: Self explanatory
Don't check my github! It contains thousands of lines of spaghetti code in many different languages cool software! https://github.com/Sulunia

Roland_Yonaba
Inner party member
Posts: 1562
Joined: Tue Jun 21, 2011 6:08 pm
Contact:

### Re: Mini Functions Repository

Sulunia wrote:Clamp function
A shorter version :

Code: Select all

local function clamp(value, min, max)
return math.min(max, math.max(value, min))
end
Or in case you need to assign the value within the function :

Code: Select all

local function clamp(value, min, max)
value = math.min(max, math.max(value, min))
return value
end
This cheatsheet would be probably useful.

marco.lizza
Citizen
Posts: 52
Joined: Wed Dec 23, 2015 4:03 pm

### Re: Mini Functions Repository

Sulunia wrote: Lerp funtion [...]
For the sake of numerical stability and math optimization, a LERP function is better written as follow.

Code: Select all

function lerp(a, b, rate)
return a + (b-a)*rate
end

Sulunia
Party member
Posts: 201
Joined: Tue Mar 22, 2016 1:10 pm
Location: SRS, Brazil

### Re: Mini Functions Repository

marco.lizza wrote:
Sulunia wrote: Lerp funtion [...]
For the sake of numerical stability and math optimization, a LERP function is better written as follow.

Code: Select all

function lerp(a, b, rate)
return a + (b-a)*rate
end

Numerical stability? Math optimization? Care for some elaboration? (genuinely curious)
Don't check my github! It contains thousands of lines of spaghetti code in many different languages cool software! https://github.com/Sulunia

marco.lizza
Citizen
Posts: 52
Joined: Wed Dec 23, 2015 4:03 pm

### Re: Mini Functions Repository

Sulunia wrote:Numerical stability?
Lua threats each number as a floating-point number. By definitions floating-point numbers are approximated and operations need to be taken with care in order to avoid (or at least to keep low) error propagation. By dismissing the additional multiplication we let the error propagate less quickly (in general multiplications propagates errors more quickly that additions, especially when numbers have big differences in the exponent).
Sulunia wrote:Math optimization?
To be honest, this should be called "peephole optimization", since we are only considering a small part of a source-code (a single formula) and reorganize it by reducing the amount of math operations involved. Your version features an additional multiplication that we can get rid of (and remember that in general, and especially on embedded devices, multiplication is by far the most costly operation).

Sulunia
Party member
Posts: 201
Joined: Tue Mar 22, 2016 1:10 pm
Location: SRS, Brazil

### Re: Mini Functions Repository

Thanks for the insight! It's actually pretty feasible what you said.
Don't check my github! It contains thousands of lines of spaghetti code in many different languages cool software! https://github.com/Sulunia

marco.lizza
Citizen
Posts: 52
Joined: Wed Dec 23, 2015 4:03 pm

### Re: Mini Functions Repository

You're welcome, @Sulunia!

Inny
Party member
Posts: 652
Joined: Fri Jan 30, 2009 3:41 am
Location: New York

### Re: Mini Functions Repository

We had another thread with a lot of small functions in it if you want to have a peak through that: viewtopic.php?f=4&t=77599

As long as we don't start the lua equivalent of NPM's leftpad disaster, I'm all for these kinds of threads. It's a good resource for newbies to learn how different pieces of code would be written.

pgimeno
Party member
Posts: 1903
Joined: Sun Oct 18, 2015 2:58 pm
Location: Valencia, ES

### Re: Mini Functions Repository

marco.lizza wrote:For the sake of numerical stability and math optimization, a LERP function is better written as follow.

Code: Select all

function lerp(a, b, rate)
return a + (b-a)*rate
end
I disagree. My own experiments show otherwise:

http://math.stackexchange.com/questions ... erpolation

The version that you've written may go past b even when rate is still < 1. See examples in the above link.

Basically, a*(1-rate) + b*rate guarantees that when rate = 0, the result is exactly a, and when rate = 1, the result is exactly b. The experiments show that it's also monotonic (edit: even if no one was able to give proof).

On the other hand, a+b-a does not always return b.

Edit: The example as a Lua program:

Code: Select all

t = 0.9999999999999999
A = -0.3465728856142666
B = 0.653769243987566
assert(t < 1)
assert(A*(1-t)+B*t <= B, "A*(1-t)+B*t is > B even if t < 1")
assert(A+(B-A)*t <= B, "A+(B-A)*t is > B even if t < 1")

--[[
Error: main.lua:6: A+(B-A)*t is > B even if t < 1
stack traceback:
[C]: in function 'assert'
main.lua:5: in main chunk
[C]: in function 'require'
[string "boot.lua"]:428: in function <[string "boot.lua"]:274>
[C]: in function 'xpcall'
--]]

Update: Comparing single-precision with double-precision results using both methods yielded the exact same maximum and minimum errors in the exact same t values. Test program: http://www.formauri.es/personal/pgimeno/pastes/lerp.c

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