Here are a few functions that have been shared in the community over the last 25 years:
Transparency Functions
simple-fade-off (evenly from start)
transparency = lifetimeI
simple-fade-up (evenly from start)
transparency = (1-lifetimeI)
approx-fade-off
transparency = sin(lifetimeI)
normal-fade-off (over life)
transparency =sin(lifetimeI*1.5)
normal-fade-up
transparency = cos(lifetimeI*1.5)
fade-in-out (over life)
transparency = sin(lifetimeI*3.14)
fade-in-out+cnt
transparency = power * ( sin( lifetimeI * 3.14 ) )
This is better than transparency = lifetimeI because with the previous formula you would have particles ‘pop’ on and then fade. I had some popping occur when I was trying to make smoke from a chimney, but it gave this interesting puffing effect.
fade-midway+cnt
transparency = transparency / sin(lifetimeI) * power
fade down in the middle of the particles life, with power control (power is between 0 and 1) (control with power)
fade-up-off-fast
transparency = -0.05(pow(tan((lifetimeI-0.5)/0.37, 2)) +1
Produces a very steep up flat top , very steep down curve, no explict control.
fade-up-out+cnt2 (use magnitude>1)
transparency = -(magnitude*lifetimeI) (lifetimeI - 1)
trans-near-a-point
transparency = 1 - smoothstep(100,400, length(pos-(100,0,500))))
In this case only near coordinates 100,0,500 - the old light default location, 100 and 400 define the distances close and far - that limit the transparency. I used this when I wanted rain to light up around a street light, - unlike a matte it works in 3 space, like a ball - when the rain enters the ball it lights up- very nice
fade-off+cnt
transparency=pow(lifetimeI,magnitude)
fade-up-off-random
transparency = sin(lifetimeI + turbulence(pos,1))
A great function that acts more naturally in fading off particles
linear-fade-up-off+cnt
transparency = ( ((1-lifetimeI)<power)*smoothstep(0,1,(1-lifetimeI)/power)) + (((1-lifetimeI)>=power)*smoothstep(0,1,lifetimeI/(1-damping)) )
This amazing function allows you to move the mid point of the fadeup/off and effect the out (via damping) try damping = 25% and power =0.5
linear-fade-up-off+cnt2
transparency = (((1-lifetimeI)<power)*(1-lifetimeI)/power) + (((1-lifetimeI)>=power)*lifetimeI/(1-damping))
fade up to frame set by power -fade down from frame set by damping (don’t use damping values lower than power) -change damping to power if you want it to fade up and down immediately. Try power=0.25, damping=75
hold-then-off
transparency = (lifetimeI>0.5)*lifetimeI + (lifetimeI<=0.5)*0.5
(lifetimeI>0.5) returns 1 when lifetimeI is greater than 0.5 and zero when lifetimeI is less than 0.5
and likewise (lifetimeI<=0.5) returns 1 when lifetimeI is less than or equal to 0.5 and zero when lifetimeI is greater than 0.5 thus multiplying the then and else functions by their respective conditional expressions and adding them together results in transparency fading down to 0.5 until halfway through the particles life and then remaining at 0.5 till the end…