Portal Mode ?

[bernhard]

Hello friends !

Today it's the first time I would like to make some tests with the Vray Light in Portal Mode.
I was searching in the forum for some answers, and how, when & where to use that light, but couldn't find answers to my basic questions:

- where do you usually use the portal mode ?
- how can you activate it and find it in 3dsmax ?
- what's your experience using it ?
- what's the advantage/disadvantage of the portal mode ?

or maybe there is a link to any thread or tutorial I couldn't find and will answer all the question above.

thx a lot for every little help,
bernhard

[MoonDoggie]

- how can you active it and find it in 3dsmax ?
A portal light is just a vray light set to portal mode (simple or non-simple)

- what's your experience using it ?
Low, but there is a great image of the use of it on the boards, it's by sv I think and it's a dimly lit room with a strange magenta light in the center

- what's the advantage....
It forces vray to collect more samples in the gi in the area. Set to simple mode, it assumes only environment is behind the light and only samples the environment.

[sv]

- what's your experience using it ?
Low, but there is a great image of the use of it on the boards, it's by sv I think and it's a dimly lit room with a strange magenta light in the center

thanks MoonDoggie - this is the thread:
http://www.chaosgroup.com/forums/vbu...ht=portal+high

I use them all the time - it's a way of telling vray the direction that GI light is coming from, and thus to take more samples from this location / direction. Typical usage would be to model a room with windows, setup a camera inside, turn on a GI environment like a VraySky and render the image. It can be quite hard to get a nice lighting result inside if this is the only light source - at least you might have to put the irradiance map to high, or take more samples in a lightcache for example. If you then put vray lights at the windows in portal mode, they will not change the lighting intensity (unlike putting normal Vray Area lights at the windows which i think can cause a fake-ish looking overall light), but the difference is they will let Vray know to sample more from this area, like they tell Vray the direction the light is coming from and produce much nicer lighting quality.

[bernhard]

hmm...

Well, sounds really good. Never tried this before, but now it's really time.

Ok, and just to understand right.
if you check the simple mode you use the bg image from the environment slot, instead of using the GI override, or ?

hmm well, how about animation ?
ever tried in animation ?

My first test showed me, that it really increases the rendertime a lot.
Also, how do you control the strength of the portal light ?
it seems to be, if checked, I can't controll anymore the value of the light source.


thx a lot,
bernhard

[sv]

If you then put vray lights at the windows in portal mode, they will not change the lighting intensity ....... but the difference is they will let Vray know to sample more from this area, like they tell Vray the direction the light is coming from and produce much nicer lighting quality.

you don't - it's a way of telling vray where another GI light source is coming from, making vray sample more from this area.

so it's not really a light in this sence, but it tells Vray where GI light is coming from basically, and to sample from here.

[MoonDoggie]

Excellent, thanks for the tips sv!

[bernhard]

hmm

well, yeah makes much more sense now - thx for your explaination, that's really great.
have you ever used it for animation renderings ?

thx,
benrhard

[sv]

well, yeah makes much more sense now - thx for your explaination, that's really great.
have you ever used it for animation renderings ?

thx,
benrhard

of course!

[bernhard]

samples ?

ok, and when you made your animations, what's the value of your samples for the portal mode vray light ? so that you don't get any flickering.

thx,
bernhard

[Aldaryn]

it's a way of telling vray the direction that GI light is coming from, and thus to take more samples from this location / direction.

Hmm, isn't it used to simply render the illumination of the are covered by the portal light in a direct light tracing mode, so you can get a per pixel detail on those areas, with efficient (rendered as direct light, not as gi) sampling?

I always thought that a portal light behaves just like a normal light, but it gets its color and intensity by tracing rays behind the portal, and forarding that what it "sees", so hence the name "portal".

I know, for example, in fryrender it is used to direct the sampling direction, but I believe in VRay it's a bit diferent. For example, you can use portal lights without any GI at all, to get, for example, a color maped direct traced VRay light source. (by putting a VRayligth shader with map behind it)

And so, the advantage is better, and detailed illumination of areas over biased GI methods, and actually has no disadvantage, since the only drawback sometimes is speed (over a rough irradiance map eg.) but you know you'll have to trade that in for some extra detail.

I'm really curious.

Best regards,

A.

[vlado]

The portal is indeed calculated similar to a direct light like Aldaryn says, so that most of the details come from the portal light, and the smooth GI is handled by the irradiance map.

Best regards,
Vlado

[sv]

Hmm, isn't it used to simply render the illumination of the are covered by the portal light in a direct light tracing mode, so you can get a per pixel detail on those areas, with efficient (rendered as direct light, not as gi) sampling?

I always thought that a portal light behaves just like a normal light, but it gets its color and intensity by tracing rays behind the portal, and forarding that what it "sees", so hence the name "portal".

I know, for example, in fryrender it is used to direct the sampling direction, but I believe in VRay it's a bit diferent. For example, you can use portal lights without any GI at all, to get, for example, a color maped direct traced VRay light source. (by putting a VRayligth shader with map behind it)

And so, the advantage is better, and detailed illumination of areas over biased GI methods, and actually has no disadvantage, since the only drawback sometimes is speed (over a rough irradiance map eg.) but you know you'll have to trade that in for some extra detail.

I'm really curious.

Best regards,

A.

cool