fadein-fadeout effect using PWM in nodeMCU LUA for use with ESPtoy for example

nodemcu-pwm-fader.lua

redPin = 2
greenPin = 1
bluePin = 4

pwm.setup(redPin,500,0)
pwm.setup(greenPin,500,0)
pwm.setup(bluePin,500,0)

pwm.start(redPin) 
pwm.start(greenPin) 
pwm.start(bluePin) 

green,red,blue = 1000,0,0

function brightness (x, max)
  return math.floor((math.floor((x * max) / 100)*2) + 1)/2
end

step = 2
dir = 1
cntr = 0

r = red
g = green
b = blue

function fader()

    if cntr > 100 then
        dir = -1
        cntr = 100
    elseif cntr < 0 then
        dir = 1
        cntr = 0
    end

    r = brightness(cntr, red)
    g = brightness(cntr, green)
    b = brightness(cntr, blue)

    cntr = cntr + (step*dir)

    pwm.setduty(redPin,r)
    pwm.setduty(bluePin,b)
    pwm.setduty(greenPin,g)
end

tmr.alarm(0,25,1,fader)