Opacity Tex Gain - What Does It Do Exactly?

[vinz9]

Hi,

I've been playing with non dynamic textured fluid, and I don't really get how the opacity tex gain slider works, especially in conjonction with the amplitude slider.

With opacity set on center gradient, a perlin noise, and amplitude set to 0, if I move the opacity tex gain slider, between 0 and 1 it makes my fluid ball smaller and then after 1, it makes it bigger.

I would have thought it would have no effect, with amplitude 0.

If I turn inflection on, still with amplitude 0, at 1 and after, my ball disappear.
This I think I understand since inflection is abs(noise)*2 -1, so always -1 if the noise is 0, but the above observation doesn't make sense.

Just curious about how the noise is added/scaled with the various parameters, can't figure it out.

Thanks a lot

[joojaa]

No variation does not mean no value. Only a value of 0 would not be affected by the gain (but would be affected by offset).

QUOTE
, so always -1 if the noise is 0, but the above observation doesn't make sense.

No any other value then 0 WILL scale. Mayas not some sort of 8 bit imaging application for maya a negative value is just that a value among others. And it will scale accordingly. No imagainary 0-1 limit is in place.

QUOTE
makes my fluid ball smaller and then after 1, it makes it bigger.

See the ball is now inverted so once it stops being point shaped it starts becoming a ball wich just has grown out of itself again. (1-1= but 1-2 =-1 wich looks exatly like a ball of radius 1. Its just inside out)

If you had any other shape, except perhaps a cube, you wuld have seen this coming.

[vinz9]

Thanks for the answer, but I don't get it.

Let's say x is the value before the noise and the opacity ramp look up.

Since I have a center gradient, x is 1 at the center and 0 on the edge.

Now what is done to x with the noise ?

I thought about something like x + opacitytexgain * (noise), but it's not it.
With a perlin noise and amplitude 0, the noise has always a value of 0, unless I'm mistaken.
So how come opacitytexgain still has an effect ?

Thanks a lot.

[joojaa]

Gain is applied after all computation. So its global for any channel. Its just a raw multipler for output, of any combined computation. Just like the volume controller in a audio device. (and yes only very few audio devices are free of residual levels)

so more like: (x +noise*amplitude/2)*opacitytexgain

So whatever residue you have is whats causing the scale.

QUOTE
With a perlin noise and amplitude 0, the noise has always a value of 0, unless I'm mistaken.

Yes in theory. but see since perin noise is used on something its usually ofset by some value to make sense for anything. So its center is defined by application, and more often than not ist not exactly 0. whet this other is depends on use. Also the noise maya uses is not entirelty symmetrical olr scaled to some specific -1 +1 ragnge as its a bit hard to do. (ask pixar they have done many years of work to get a noise thats not biased and is in range)

So in practice your as likely find noises that center on 0, 1 0.5 and so on.

But yes your seeing scaling of the channel. Which is not 0.

In any case whatever you think is something makes no difference whatsoever, Just what is. maya shaders ar black boxes so you can not know what they do isnide themselves. Just read output.

And the effect you describe makes perfect sense.

[vinz9]

Thanks, but I still don't get the (x +noise*amplitude/2)*opacitytexgain.
In that case when opacitytexgain is 0, everything should be 0 whereas in reality when opacitytexgain is 0 the texture has no effect.
So I thought about something like x*(1-opacitytexgain) + (noise*amplitude/2)*opacitytexgain but it seems strange.

x + opacitytexgain * (noise) actually makes more sense if the noise is not 0 with an amplitude of 0.

[joojaa]

QUOTE
everything should be 0 whereas in reality when opacitytexgain is 0 the texture has no effect.

Everything = 0 and texture has no effect is the same thing.

Anyway it depends on what your x is its the the opacity gain only affect the perlin noise section so if x is in your mind representing the different sections form the outside then its.

x + (noise*amplitude/2+y)*opacitytexgain

where y is the coefficient that is the actual offset of the perlin noise. It might be 0 but it hasnt got to be so. If you talk of locality then it can be asumed you think o the locality only.