refracted sunlight urgent!!!

[Free Agent_cg]

can anyone tell me why sunlight has trouble coming through a pane of glass with refraction on? i cant get my sun to come through a big glass curtain wall it shows a few big light "spots" here and there but thats it... ive always had problem with sunlight and refraction, specifically refraction, but lately for hiper realism you need it so these old issues arrise can anyone help???

[dalomar_cg]

Re: refracted sunlight urgent!!!

As typical of me, I've got another long answer, short answer response for you...if you're busy go with the short answer...if you want to know WHY, then go with the long one...if you don't want to read then go to the next thread ;D

Short Answer:
If you go to the refraction layer in the material in question, there is a parameter under the Fog settings called Affect Shadows. Enable that and you should be good.


Long Answer:
The problem is because of what is needed to calculate different types of light bounces. Most light transport algorithms are setup to deal with diffuse indirect illumination, but don't do very well with simulation of caustics. Caustics are any light that is affected by materials with reflection or refraction. In this case light passing through a window is actually a caustic calculation rather than a diffuse calculation, and therefore must be calculated by a method that will support caustics. The only way to really do this in V-Ray is essentially through photon mapping (although photon diffuse calculations and photon caustic calculations are separate). And in enters the other issue (don't worry there's light at the end of the tunnel)...

Photon mapping is a pretty old technology and relatively primitive when you're talking about some of the other calculation methods that are available. One "symbol" of its primitive nature is that it has a severe limitation that in order to simulate photons it has to have a "physical" source to shoot them from. This means that it can't simulate GI because it doesn't really "exist". In terms of the V-Ray sun, it doesn't really "exist" either (parallel/direct light sources in V-Ray have no beginning or end in V-Ray), but in other platforms you can place the actual light, and therefore give it a location in which to shoot photons from. Unfortunately for numerous reasons, there is no placement of the sun in SketchUp. For everything else that the sun does, placement doesn't matter, but just by this one aspect, shooting photons from the sun just plain won't work.

So it sounds like we're screwed, but in fact were' not. If everyone had to do caustics calculations when shining light through a window, then a lot of people would be screwed and annoyed as caustics are just generally a pain in the arse to deal with. Luckily though, there's a tiny little setting that will save the day (here's the light). In the Refraction layer, just under the Fog parameters, you will find a little check box labeled Affect Shadows. This is a nifty little setting that will actually fake a caustic affect by retracing direct light that goes through a material. The result is light passing through refractive materials in a manner that is similar to caustics, but doesn't have all of the annoying setups or calculations associated with it.

[Free Agent_cg]

Re: refracted sunlight urgent!!!

where would we be without you
Dalomar for president!!! ;D

can you give me another long answere as to why my chrome refracts/reflects black? is this another caustics issue? starngly enough it only seems to be happening to chrome.

[dalomar_cg]

Re: refracted sunlight urgent!!!

Nope, not a caustics issue. Its also much more simple...Basically, reflection/refraction has a tendency to have render times go through the roof, especially when you're talking about reflections within reflections within refractions within reflections So, V-Ray keeps tabs on how many times a given ray has been reflected or refracted, and if it does that too many times V-Ray stops calculating that ray. By default we have this pretty low (2) since this isn't a situation that pops up very often and can help speed things up. Usually I find 5 a good mid setting and 8 a higher setting, and I set those depending on whether the scene needs it.

[nomeradona_cg]

Re: refracted sunlight urgent!!!

where would we be without you
Dalomar for president!!! ;D

can you give me another long answere as to why my chrome refracts/reflects black? is this another caustics issue? starngly enough it only seems to be happening to chrome.

yeap lets vote for damien.

[Free Agent_cg]

Re: refracted sunlight urgent!!!

Dalomar please excuse my ignorance, but u said but u refer to numbers as low to mid to high settings, what number exactly there are quite a few in the v-ray interface :P

[dalomar_cg]

Re: refracted sunlight urgent!!!

I'm sorry, I got so caught up in the (not so) long answer that I forgot to actually say what the setting was...(drum roll please) Max Depth in the top left corner of Global Switches. ;D

Thanks for the nods for the presidential ballot, but I'm not much for campaigning...although expensive dinners are usually pretty good ;D

[Free Agent_cg]

Re: refracted sunlight urgent!!!

fantastic thank you! seriously i see zimbabwe could use a new president... any thoughts?

[dalomar_cg]

Re: refracted sunlight urgent!!!

Zimbabwe...thats a long way a way from my current home...