rendering foam with shadow slow

[jstrob]

Hi,

I am trying to render some foam for the first time. What I notice is when I activate the shadow it becomes incredibly slow to render. Without shadow it is pretty fast. I have two rectangular vray lights for shadow casting. and my foam is in splash mode. Do you have any tips for rendering foam with shadow faster?

[Ivaylo Katev]

all the area lights use multiple rays to calculate the shadows, by default they can reach up to 256 lights (the square of the subdivision number)
and this is not all, actually single camera ray produces multiple requests for shadow calculation.
you can resolve performance problems seeing in the vray messages window, there is briefly described the count of the different rays used to calculate the image.
when you see that given feature produces too many rays, you can decrease the subdivisions or to make other tricks to avoid the huge ray number.

[jstrob]

Ok I could try to render my foam pass using spot light with shadow map maybe..

[ivaylo.ivanov]

Shadow maps are hardly working for simple geometry, I doubt you can use such antiquated methods for foam. Directional light or two with shadows should be fine. Just be careful with area lights since the foam is acting more like volumetric then geometry. Svetlin is doing some tests to use probabilistic shading of foam. It's working well with the point shader, but the other methods are more complicated and tend to produce too much noise.