rectangular area lights?And interior lighting(<=>MR portal light

[nmn]

Hi everyone,I need your help on this one

In fact i have 2 questions

1-can a Grid area light be rectangular, and if yes how?

2-what would be the equivalent in mantra of mentalray's portal light, and

how would you go for rendering an interior scene with light coming through a window?

Thanks for your help

Best regards

Edited May 3, 2009 by nmn

[DaJuice]

Hi nmn,

For part 1 of your question, you can parent a null to your light and scale the null.

[Jason]

For part 2, there is no portal light yet - but SESI are aware of it and they say they'd like to add it.

[nmn]

Thanks for your answers guys,

@DaJuice :

- in fact i tried going inside the light node and scaling up the thing in there,

the shape grew up but it didn't affect the lighting, thanks for the tip.

- what GI method did you use for your scene, coz it's very nice and smooth, and what about render time?

- ah and one more question, how do you make the area light visible :|, or u did use a rectangle with constant shader ?

@Jason :

- Thanks for the info, but in that case how would we go to make an interior scene lighting, with light coming in from the windows ?

i found a node called vex Window but after playing a little bit with it i realized that it's not something for such cases

Regards

Edited May 4, 2009 by nmn

[DaJuice]

- in fact i tried going inside the light node and scaling up the thing in there,

the shape grew up but it didn't affect the lighting, thanks for the tip.

- what GI method did you use for your scene, coz it's very nice and smooth, and what about render time?

- ah and one more question, how do you make the area light visible :|, or u did use a rectangle with constant shader ?

Yeah that's the first thing I tried as well and was surprised when it didn't work. The scene is PBR with 32x32 samples, rendertime was roughly ~30 min for each on my laptop (1.6ghz), wasn't really paying too close attention. The visible light is just a grid with constant shader and channel references to match the size and position of the null/area-light. It's excluded from shadow-casting in the area-light so it doesn't destroy the lighting in the scene.

As far as the other thing, the portal light is to avoid problems with light going through glass first...?

[nmn]

Yeah that's the first thing I tried as well and was surprised when it didn't work. The scene is PBR with 32x32 samples, rendertime was roughly ~30 min for each on my laptop (1.6ghz), wasn't really paying too close attention. The visible light is just a grid with constant shader and channel references to match the size and position of the null/area-light. It's excluded from shadow-casting in the area-light so it doesn't destroy the lighting in the scene.

As far as the other thing, the portal light is to avoid problems with light going through glass first...?

Thanks for your answer DaJuice , that was exactly what i thought about the rectangular white shape

in fact the portal light was introduced at the beginning to address the problem of let us say, you have a room in side which there is no lights, and outside this room you have a sky light, if you just render the inside of the room using for example FG , the chances that your rays will hit the window-get outside-and get light information are not that high, so either increse the number of rays so some crazy values and wait ages (and i doubt it will get the required result),or use a portal light (i'm simplifying a bit here) on your window that will act as the transporter of light from the outside to the inside so you get the expected result.

BTW isn't there a fast way to get such results in houdini, all the methods i try, like irradiance inside the material, or vex GI, or PBR ...etc all are very slow for decent results :S, while with MR you can get comparable results for a lot smaller time, or there is some things i'm missing here ... :|

Cheers

[DaJuice]

Thanks for your answer DaJuice , that was exactly what i thought about the rectangular white shape

in fact the portal light was introduced at the beginning to address the problem of let us say, you have a room in side which there is no lights, and outside this room you have a sky light, if you just render the inside of the room using for example FG , the chances that your rays will hit the window-get outside-and get light information are not that high, so either increse the number of rays so some crazy values and wait ages (and i doubt it will get the required result),or use a portal light (i'm simplifying a bit here) on your window that will act as the transporter of light from the outside to the inside so you get the expected result.

Ahh okay that makes sense, it directs the attention of the renderer to the interior basically. Well I'm not sure how mental ray's GI is classified but I believe the path-tracing in PBR modes is bi-directional, so it should take the camera into account when it goes off shooting rays. But yeah those are noisier scenes to render. MLT seems to be very good in those scenarios: http://graphics.stanford.edu/papers/metro/

There was a really rough version of MLT in 9.5 but I think it's gone now.

BTW isn't there a fast way to get such results in houdini, all the methods i try, like irradiance inside the material, or vex GI, or PBR ...etc all are very slow for decent results :S, while with MR you can get comparable results for a lot smaller time, or there is some things i'm missing here ... :|

Right now I think we're sort of limited to a brute-force approach with PBR, but I think on the SESI boards AndrewC mentioned something about a replacement for view-dependent photons to help speed things up. Have you looked into read/write Irradiance caches for the regular GI? Might be of use.

Edited May 4, 2009 by DaJuice

[nmn]

Hey again, i wanted to do some tests before rewriting here, and the results were somehow disappointing, so am i doing something wrong ? or is it really like this ...

so basically i have a scene consisting of a big room or hall , inside which there are a bunch of objects mainly cubic objects ntg fancy, so this hall is closed no lights are lit inside, and it has some windows, and the objective was to light this hall ... through the windows.

for that i tried many approaches :

- objects with constant shader on the windows

- area lights on the windows

- directional light coming from the windows ( alone and also combined with each one of the above )

and with each one on the above methods i tried with the vex gi light, i tried with PBR and i tried with an irradiance node added to the materials in my scene.

after a looooot of tests i got something that may be acceptable, with irradiance node inside the material (in fact i sticked only one white material on all the objects) but but but for 8x8 pixel samples, 128 samples for the irradiance node and a 640x480 image on a quad core! it took more than 2 hours to get to like 33% !!! - not acceptable

so as for my scene up until now i didn't find yet any good and viable approach to get my result ...

(if you need the MR way explained just tell me, coz i did a fast test with MR in Maya, and well ... a decent result can be obtained for like 2~3 minutes render time...)

any ideas ?

Best Regards

Edited May 5, 2009 by nmn

[symek]

Could you post your scene along with mr render for comparison. AFAIK Mantra will proceed slow in a scenario you've described, but 2h for 33% sounds suspecious.

thanks,

skk.

Edited May 5, 2009 by SYmek

[dbukovec]

maybe i'm mixing techniques, but adding irradiance caching to pbr would speed it up tremendously, ala modo? or im totally wrong here?

Edited May 5, 2009 by dbukovec

[nmn]

Hey guys,

@SYmek: not allowed to show things ... , but for more details please feel free to ask me ...

i know lighting an interior just from the window is a little bit tricky, that's why they created the portal light light shader for MR...

in such a scenario what would be the best way to go in your opinion with mantra of course

@dbukovec: in the one with 2hours for 33% i'm using raytracing along with an irradiance node added to the material... so no pbr

Cheers

Edited May 5, 2009 by nmn

[symek]

maybe i'm mixing techniques, but adding irradiance caching to pbr would speed it up tremendously, ala modo? or im totally wrong here?

pbr with irradiance (also cached) would slow it down most probably. Although interestingly it seems that both gather() and pathtrace() can utilize irradiance cache if needed. Funny enough you could create a cache in pbr mode(pathtrace()) but use it with occlusion shader. So while pathtrace() is slow solution, it is possible to bake it for later use with micropoly or raytrace. Not sure about practical aspects of such trick.

@nmn: if you can't show the scene, prepare an example, so we could compare results. As I said, I expect Mantra to be slower that mr in interior scene, but not in a ratio you've described.

cheers,

skk.

Edited May 5, 2009 by SYmek

[nmn]

i'll do some more tests, and i'll try to prepare an example scene ... that doesn't ressemble the real one, to avoid beeing hanged lol

Cheers

[DaJuice]

i'll do some more tests, and i'll try to prepare an example scene ... that doesn't ressemble the real one, to avoid beeing hanged lol

Cheers

Yes please, that would be good.

[dbukovec]

I was talking about adding irradiance caching to pbr, like modo does, if You turn off irrad caching in mode You have a path tracer like engine, and modo's render engine is insanely fast. Thats why i asked do i mixing stuff up? Maybe adding irrad caching to pbr does not make any sense in technical world.

[nmn]

Hey

Sry it's been heavily busy around here so i didn't have much time to create the test scene and do some tests on it (which may take looong) ... etc

but i'll try to describe the process really quick:

- create a box, scale it like 35 15 35

- make it poly mesh, increase the divisions to like 8 4 8 or smtg

- make few holes on the top part

- extrude all the faces, to give it some thickness (don't forget to turn on back faces)

- create a directional light, and position it in a way that when you look from it you see your whole box and at an angle let's say of 45 degrees, then turn on its ray traced shadows and make its intensity a little bit higher, like 10 or 15 ...

- create a basic material - inside it just add an irradiance node and add its output to the result with an add node - then assign it to the box (you may take down the samples a little bit down to like 128 ...)

- create mantra node set rendering to ray trace engine, set samples to let us say 6x6

- create a camera on one corner of the box that looks to the inside of the box and voila Hit render ... and waiiiiiiiittttt

sry again about not posting a scene...hope the description will help a bit

Best Regards

Cheers

Edited May 7, 2009 by nmn

[nmn]

Hi again, and sorry for not having time before

so here you go, i had a few minutes so i created the famous scene, it's attached to this post.

Thanks for your help

Regards

test.hipnc

[stevenong]

Hi,

I don't know what's wrong with your file but I set up another like it & the render time is way down.

I've attached my file. Using the mantra ROP with raytracing, the render took 35 secs. I set up a PBR ROP as well.

If your render time is way longer using raytracing, say 5 mins, I suggest you rename or delete your $HOME/houdini10.0 directory. You might have accidentally saved some default settings for your mantra ROP which is causing the slowdowns.

The file was created with 10.0.259.

Cheers!

steven

odforce_room.zip

[DaJuice]

Your file renderered verrrrry slowly nmn. Not sure why, didn't really investigate.

Here's the scene setup with Irradiance GI (via light template). Is there a reason in particular why you're trying to have it at the shader level?

Anyways, on a 1.6ghz core2duo laptop this took 23 minutes to render. Once that render was finished though and the irradiance cache written, repeating the render only took 26 seconds.

test_edit.zip

[nmn]

Hi guys and thanks for your answers, now i'm really very very puzzled

Your file renderered verrrrry slowly nmn. Not sure why, didn't really investigate.

I don't know what's wrong with your file but I set up another like it & the render time is way down.

I suggest you rename or delete your $HOME/houdini10.0 directory. You might have accidentally saved some default settings for your mantra ROP which is causing the slowdowns.

i can't understand why my file would render lot slower with the same setup, i even tried that setup on 3 machines here already and same result !!!

for my last test (the one i uploaded to you) i chose a machine that never had houdini on it, i dlded it, installed it, and i didn't change anything, i left evertg as default, then i did my setup and it came out the same, slow as hell!!!

@steven : thanks for the files, but DaJuice's way is what i'm after atm, because in yours the light is mostly coming from the area light, and the irradiance effect is minime.

@DaJuice :

Is there a reason in particular why you're trying to have it at the shader level?

in fact i thought if i restrict the irradiance to the material it would be more efficient (i know in this scene there shouldn't be much of a difference since we have only one material but that was the idea) so what do you think about that.

i have a problem with your scene, and i played around with it and i couldn't solve it ... it's rendering very dark :S, i even kept pumping up the directional light intensity to 5000!!! and ntg has changed (i turned off the irradiance caching and tried, also no change) ... soooo i'm really puzzled here ...

one more thing can you please DaJuice explain to me a little bit about the irradiance cache? especially when is it used and with which setups?

Waiting for your answers guys coz i'm really in the dark atm regarding all these stuff ...

Thank you very much.

Best Regards

Edited May 8, 2009 by nmn