What's the crack with refraction?

[Matt Sugden]

So last night I set a render off before i went to bed, as my current scenes on this project are taking about 9 hours, and i thought it would be mostly done by the time I got up.

 

Foolishly I hit the raytrace refraction map on a material for a tiny glass vase way in the background as i thought it would be nice for a change for the glassware to look semi real, and low and behold this morning my render had completed 0 buckets. NONE.... NOTHING in 9 hours!! ;o(

 

So what are people's solutions for getting a semi convincing dense glass, are people using refraction and just putting up with astronomical render times, at the moment I've been avoiding it like the plague. Are people using different levels of opacity in the glass material to fake it for instance or are there anyother tricks. I'm using a global illumination solution in max. Is raytrace the wrong setting?

 

Cheers, I'm off to cry infront of my screen, while I wait another 9 hours!!

[IC]

Hi Matt

Adding raytrace+GI=bad render times.

 

I always use 'raytrace refraction' on glass objects but I use LightWave with FPrime so there is no real difference in render time.

 

You can often get away without refraction by putting a subtle bump on the material and using a variation of the 'air material' trick:

Copy the object, flip its normals and scale it down slightly so it fits inside the original. This gives a distortion on the glass twice as you look through it and can look very much like refraction.

This is quicker than using 2 sided materials and also gives variation to the distortion.

[Matt Sugden]

Thanks for you're reply Ian, and I've had a quick go this afternoon and posted the results below.

 

I must say it's not my best work!!

 

when you create the smaller version ian do you lathe based on the object being hollow, as is, or do you create the vase/bottle as a solid?

 

Ta

[IC]

Both objects are hollow.

I think your image needs an environment to reflect and it would look much better.

 

I'll post an example later.(Got a 2 year old climbing over me wanting to "paint on the 'puter")

[Alex York]

Are you rendering in passes? if you use passes, you can set up a very simple raytraced reflection pass, raytraced refraction pass, diffuse&GI pass and comp them together. that way you can turn off GI for the raytraced passes so rendertimes will be drastically lower.

[William Alexander]

Look at using fall offs and or 'Frensel' with local minimized raytrace settings for the glass.

 

Here is a handy link to a smoke3d tut, that maybe helpful-bottle info is 1/2 into it.

http://www.cgarchitect.com/resources/tutorials/smoke3d/tutorial16.asp

 

It's a max tutorial, but principle can be applied in many apps

 

Cheers

WDA

[IC]

Here's a test I did with no refraction.

Pile on the subtle bump and reflection and it's almost convincing.