does frosted glass slow down your renderer?

[Ernest Burden III]

I have been pleased to be able to create a frosted glass material in Lightscape that behaves in a very realistic way. But when that material is used in a model and is visible in a view, raytracing a render goes from 15 seconds to 5 minutes. Not a problem on single-view renderings, but it makes using that material in animation almost impossible.

 

The reason for this is that I am basicly modeling real frosted glass, I use a vanishingly small bump (these are procedural in LS, so no map used) and it makes the raytracer scatter the refractions, giving different results depending on distance--just as it should. That's how real frosted glass works.

 

So my question is, how do other rendering engines handle this tough but un-avoidable (especially with one of my clients who is art-glass happpy) material?

[xgarcia]

With VRay I'm using glossy reractions / reflections. When turned on a frame that takes 50 seconds will go to around 2-3 minutes. Not bad at all for animation.

[Christopher Nichols]

Well, lets see if my explanation helps.

 

When you do a "glossiness" effect to create frosted glass, it is actually the most "correct." The ray that hits the glass is split into a number of samples and collect back as an average.

 

This generally looks the best, and has a great effect of things being more in focus that are close the glass, and more out of focus as they are far away from the glass.

 

If you don't use a glossiness but use a bump, the ray is not scattered into many rays, it is just "bent" according to the implied normal based on the bump map. This can work with a small noise map to simulate forsted glass, but is really good to get the look of textured glass or glass with a pattern on it.

 

This generally takes less time to render, but visually may not look like frosted glass, especially compared to a glossiness effect.

 

There are tricks to make transparency blurry without having to shoot as many rays. The first is the way that finalRender did in stage 0 (the last time I used it). It took the reflection and just blured it. It was super quick, and in many cases was good enough, but you lost the defocused effect.

 

Vray has the "interpotated samples." This uses the same technology that they use to collect samples for GI and applies it to glossiness effects. It can look good, but can have issues with animation unless you turn the settings up.

 

Is this what you were looking for in terms of information?

[Ernest Burden III]

Is this what you were looking for in terms of information? [/QB]

No, but thank you for a typically informative post, Chris. I was asking about balooning render times with whatever method produces the frosted glass effect. My tests in LS

forum thread and then used in some 'finished work' I posted.

 

My thinking was that the bump-based refraction was the best model of how the real material behaves. You describe this 'glossines' bit as better, which I don't see yet. I'll have to think about that.

 

All this is another roundabout way of deciding how much life Lightscape has left. I have seen frosted glass, as good as it can be in LS, vastly increase render times. I wonder if I would be in the same boat (how ironic that word is, considering my last project) with ANY renderer. That's really the question.

[xgarcia]

I guess I'm thinking of frosted glass more along the lines of "sand-blasted" finish. VRay refraction glossines handles (simulates) this very well IMO. I guess you could add noise bump to further the effect, creating more realistic reflections (but only close up - not worth it for far away).

[Pavel Roder]

Hello Ernest!

 

I was trying to solve the same problem and my solution was :

 

1) computing GI in LS (without any special glass/metal mat)

2) then putting it into MAX and rerendering it with Brazil mats/blurrines (with no GI)

 

- This works the best for me (i was able to render animation with a lot of steel tables / frosted glass bars). The time was quite impressing comparing it with bumped ls mats.

[John Dollus]

The render times for frosted vs. clear glass are about the same in any 3d package currently available. A multiplier of 3-5 times is common although the time differential you have experienced using Lightscape seems very large. Is the 15 second render time using the exact settings as the 5 minute time with the exception of removing the procedural bump from the frosted glass material? I suppose if the glass was taking up a significant portion of the image it could balloon that high.

[Ernest Burden III]

The render times for frosted vs. clear glass are about the same in any 3d package currently available...Is the 15 second render time using the exact settings as the 5 minute time with the exception of removing the procedural bump from the frosted glass material?

Naw, that's just if you're looking the other way, not seeing the frosted glass.

 

In this case I am stuck with the glass, I think, because it isn't just frosted, it is etched with images on it. I prepared a targe file with an alpha channel to provide the variations of transparency for the etched parts vs. the clear parts, layered this over regular clear glass. So there's a lot of light modifying going on with this material. I can't think of an easier way to do it, but maybe I should try getting rid of the bump and just adding noise to the alpha channel and live with slightly less realistic glass. I have to render it about 1500 time pretty soon at 1/2K res, so per-frame time is an issue.

 

Thanks!

[John Dollus]

Sounds like a project I did about 8 years ago. The client had a curved glass partition for a conference room that had 4 layers of sandblasted patterned etching to create a glass wall that looked like ocean waves. I ended up doing exactly what you just posted - Alpha maps for the layers with noise applied. It looked really bad by today's standards but it was 3dsR4 Dos. Ugh!

Can we see what it looks like or is this an NDA project?