Speeding up glass rendering

[tricky]

Any good tips for speeding up the rendering of glass? We are producing an animation of a whole series of office buildings. The camera moves around the outside of the buildings and then trhough the windows and into the office spaces (seperate animation/solution that we will comp together later). The rendered frames are taking around 10-15 minutes for mid distance external shots, but the renders that approach the windows - so that quite a large proportion of the render is glass - are taking 90 minutes plus! As the scene is in motion, I am not so concerned with accuracy of reflections (we will be doing a bit of post motion blur etc), but I just would like them to render quicker.

Glass material as follows:
Diffuse - black
Reflect - falloff, say 90% black to mid gray at a more oblique angle
Refract - white
Max depth override - 2

I even tried setting the IOR to 1 but it made little difference. Turning off Trace Refractions also did very little. Switching to a fixed mid-gray reflection rather than a falloff also made little difference. Is it just a fact-of-glass?

AA filter is off BTW and I am using Adaptive QMC 1,3

[percydaman]

if theres not alot of glossy or loads of small detail, maybe you should try adaptive subdivision? It was made for instances where you have large flat areas. Might work good for you scene.

Also have you tried using 1 sided planes and just using a standard material set to say 20 opacity and a vraymap for reflection? Ive found it can be alot faster at times, especially for arch glass where refraction is frankly lost.

[jacksc02]

uncheck visable to GI, it tends to speed things up a little

[tricky]

if theres not alot of glossy or loads of small detail, maybe you should try adaptive subdivision?

There are quite a few glossies - I tried Adaptive Sub but the render times went up.

Also have you tried using 1 sided planes and just using a standard material set to say 20 opacity and a vraymap for reflection?

Good idea - but it may be a bit late on this project. I'll try on the next one - if I can stomach another animation. I always start so positive and they turn into a nightmare!

uncheck visable to GI, it tends to speed things up a little

Wouldn't this just speed up the Irmap calculation and not the actual rendering? The calculation has already been done, its the rendered frames from that siolution that are taking too long.

(don't you just love the

quote

button? :P )

[jacksc02]

ahhhh I didnt know that you had already done the irmap!

[percydaman]

keep in mind that vlado once said that the longer it takes the compute the irradiance map, the longer the actual rendertime excluding the irrad map calc time. Hope that somehow makes sense