Author Topic: Skylight Portals  (Read 45512 times)

2012-10-18, 03:20:23

Sam75

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I did some quick tests of interiors and it appears that the difference (noise/rendering time) between using environment light only vs Corona planar lights on openings is quite significant.

So the question, are skylight portals on your to do list ?

2012-10-18, 08:38:30
Reply #1

Ludvik Koutny

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Nope, Corona should be quite efficient without them and from my tests, difference is only minor, almost none. Any chance you could post your renders and some description on scene setup?

A few important notes when rendering interior scenes:

1, Always make sure all objects in your scene have enabled shadow casting in objects properties. Disabling shadow casting is a fake, and fakes in Corona affect performance in a negative way. So if you intend to disable shadow casting for example on glass planes in the windows, you can actually make whole situation even worse.

2, if you have any glass in the windows, or any other light entrances to the space you are rendering, make sure geometry of the glass is only one sided (one face, no thickness) and apply glass material with glass mode set to twosided (thin). This mode not only can render objects of very thin glass without need of adding thickness to the geometry (like light bulb glass) but also does not affect rendertime at all if you use it in windows.

If you use regular thick glass with refraction in windows, any ray that passes through it is considered a caustics and your scene will take extremely long time to render...

3, For interior scenes, switch secondary GI solver to HD Cache and leave it at defaults, it is going to work well.

Don't use opacity maps for any elements covering windows (like curtains) unless you have really good reason to. For fast rendering, use just translucency and refraction level value with mode set to twosided.

I wrote this because most of the people have problems with slow rendering caused either by having glass in windows, or secondary GI solver set to path tracing on an interior scene. And then they come up with nonsenses like silly portal light, which other renderers implement because their GI solutions suck ;)
« Last Edit: 2012-10-18, 08:49:07 by Rawalanche »

2012-10-18, 22:21:05
Reply #2

Sam75

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I guess I don't need to tell which one is which.

I would not call that a minor difference.

How is using PT as second solver a nonsense ?


Gonna try Hd cache, thanks for the tip.
« Last Edit: 2012-10-18, 22:38:04 by Sam75 »

2012-10-18, 22:36:53
Reply #3

Ludvik Koutny

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I am gonna do some test to make sure i am not the one who is talking nonsense ;) So hold on... :)

2012-10-18, 22:48:05
Reply #4

Ludvik Koutny

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Ok, just did the test, and results with and without corona lights in windows are in my case identical :)

My render settings are at defaults except that secondary GI is changed to HDcache which too is left at default settings.

You can tell which is which by file naming ;)

If you still have some quality difference, you can try increasing Light samples multiplier value (Samples multiplier setting in Lights frame in Main Corona Settings rollout)

Cheers! :)

2012-10-18, 22:54:11
Reply #5

Ludvik Koutny

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Oh, and i never said using PT as secondary GI is a nonsense.... it makes perfect sense, especially in exterior scenarios with heavy geometry (foliage, grass, etc...)

I said portal lights are nonsense... And i was not exactly right. It's a nonsense in context with Corona, because we got a lot better solution for these situations. For example our environment illumination is actually done on a light basis, so you can think of our enviro light like for example Vray Dome light set to full sphere mode, or MentalRay's Built-in IBL  :)

2012-10-18, 22:56:27
Reply #6

Ondra

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ehm... the scenes are quite different. The smaller the windows are, the better using lights/portals in them becomes.

Anyways, portals will be implemented eventually, as an optional way to speed up rendering of interiors with small windows
Rendering is magic.How to get minidumps for crashed/frozen 3ds Max | Sorry for short replies, brief responses = more time to develop Corona ;)

2012-10-18, 23:00:53
Reply #7

Sam75

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Ok I just tested HD cache, much faster indeed.

HD cache GI is as accurate as PT in any situation ?

2012-10-18, 23:05:40
Reply #8

Ludvik Koutny

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Ok I just tested HD cache, much faster indeed.

HD cache GI is as accurate as PT in any situation ?

Very significant speed up at the very slight cost of accuracy, but no blotches or anything like that....  just some minor light intensity deviations...  in most situations it pays off ;)

2012-10-18, 23:13:34
Reply #9

Ludvik Koutny

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Ok, so i made the openings bit smaller, but i still observe only very minor difference.

The difference favors the version with the lights though, so some scenes might indeed benefit from portals, but the fact that difference is so small indicates that sky portals are not urgent :) Although, of course...  can come handy in future :)


2012-10-18, 23:19:56
Reply #10

Sam75

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I guess it makes more difference with PT.

I was using PT because I was concerned with blotches indeed but so far HD cache looks good.

2012-10-18, 23:24:49
Reply #11

Ludvik Koutny

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I guess it makes more difference with PT.

I was using PT because I was concerned with blotches indeed but so far HD cache looks good.

Yes, you are probably right...  and about HDcache, you should not see any artifacts unless you do an animation, where it might cause some issues. But for static renders, it should always work well.

EDIT: Btw you can create a tests thread in the gallery section and post your tests there, it would be interesting to look at ;)
« Last Edit: 2012-10-18, 23:28:14 by Rawalanche »

2012-10-21, 00:37:29
Reply #12

Javadevil

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Portal lights will be useful once Irradiance cache is up and running :)


2012-10-21, 00:39:37
Reply #13

Ondra

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ummmm.... no ;) They will be exactly as useful in both PT and IC. There is no magical reason that PT wouldnt need them. Maybe its just that the unbiased renderers are better at brute-forcing it without the portals.
Rendering is magic.How to get minidumps for crashed/frozen 3ds Max | Sorry for short replies, brief responses = more time to develop Corona ;)

2012-10-21, 17:46:52
Reply #14

maru

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In unbiased rendering a window (hole in the wall) works like a light portal, am I right? Adding extra light portal would be like adding additional data which could even make the rendering longer?
Marcin Miodek | chaos-corona.com
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