Explosion flash takes ages to Render

[Ihno]

Hi,
iam testing the latest nightly version.
Ive created a simple explosion scene with a 50m grid. rendertime for most frames is acceptable.
But the first few frames where the heat is quite high and massive light is emmitted from the fire, take ages to render.
Even in a testrender with a clr. Thresh. of 0.05 and 720p resolution.
It took more than 4 hours to get about 50% of one frame done.
I'm playing around with the lightres. And it seems to get faster but even with 0.01% the rendertime is way to high.
It converts cells to lights right? So, the higher the grid res the lower this value should be, otherwise it'll create thousents of lights on a 50mill grid right?
Are these omnilights treated like vray lights? Has the Probabilistic Lights value any inpact on it? Are there any vray settings which you recomment to swich of or on for rendering scenes like that?

Iam on the latest stable Vray version for Max 2016.
Rendering with DR on two i7 2600k @4ghz
With automatic mode and BF&LC for GI

Apart from this i'am quite exited about the new features in this version.
The massive changes in almost every part of it (as far as i can tell from now) are leading to another question:
Will the stable version be a service pack or a complete new version which we'll have to pay for?

Edit:It throws a warning: Unable to create light from node Light001.

[Svetlin.Nikolov]

Hey Ihno,

If you are using GI, you may turn off the 'Emit light' section entirely and the GI will handle the light emission automatically. However, this way you'd have much less control over the light strength, fadeout, etc. I'd rather suggest you keep 'Emit light' On and turn off GI if you want a fast render, unless you really want to achieve global illumination from colored smoke to an object or from a colored object to the smoke - otherwise the light emission should work many many times faster without GI.

You are correct that the light resolution is the way to go on getting more speed, or if you get too much noise from the emissive lights. The voxels are converted to omnies only using scanline - with V-Ray it's just a single V-Ray light that we handle internally. 'Probabilistic lights' will not affect it - the direct subdivisions in the Fire options are the way to control it. We have a new light type in mind for both V-Ray and Phoenix that will handle the emissive light case more gracefully, but this will come in the not-so-near future.

We have the light warning in our bug database, but we haven't been able to get to it yet - it's not affecting the rendering in any way, so don't worry about it

The next release will likely be Phoenix 3.0, but I can't say anything about the pricing at the moment...

Cheers!

[Svetlin.Nikolov]

PS: Apart from the GI on/off tactics, you could try Phoenix's Probabilistic Shading option - it's in the atmospheric settings - it's on by default for the V-Ray VolumeGrid, however it doesn't support Phoenix's default fire alpha setting, so it's off by default for Phoenix until we find time to deal with it.

[Ivaylo Katev]

and one more suggestion - perhaps your image sampler has too high upper limit, try with fixed sampler and if my suggestion is correct, there difference in the render times between the first frames and the next frames will disappear