Render is seemingly progressing but stuck at 0% after 5 hours

sincartier

(Asking because the posts I found about that seemed to be about 3DL, not Iray)

Now, I was out of the house for the last few hours so I don't mind the render time, but I kinda want to use my PC for the rest of the evening...

I mean the render is pretty and everything is there... just need the grain gone.  It's not a particularly complex scene as far as I can tell... except maybe a bit of a reflective floor, a bit of reflection on some school lockers and a semi-transparent (just opacity, no refraction in there)...

Any reason why it may be taking so much time?  Would I get better results if I uncheck CPU under the render options?  (Seems to help more than having it on most of the time).  

Finally, and most importantly... I know I can stop a render and resume afterwards, but I only seem to be able to if I don't save or close the current render window.  Any way to resume it later on in any other way or is my best bet to cancel the render, leave the window open, move on with my evening and resume it before going to bed?

 

Any help would be appreciated, thanks!

KindredArts

Is this a closed scene or open scene? Are you using any SSS? What GPU are you rendering on? Can you supply the image you're trying to render?

Iray is blazing fast at some scenes, and cripplingly slow at others, it all depends on the composition. An interior scene that relies on exterior lighting leaking through windows would be much more taxing than using an hdri dome to light a figure for example. I've never let a render go past 20 minutes.

sincartier

Unfortunately can't post the scene because I don't dare shut it down now.  It is a simple scene with 2 characters in the School Hallway set, bought here on Daz.  The end of the corridor behind the camera is open.

One character I know has no SSS on, the other may have it on... forgot to check.

Rendering on an i7-4790, 16g RAM, 970GTX, running on SSD.  Should still be doing good.

For my lights, I applied DzFire's Real Lights for Iray mesh lights on the neon lights in the School Hallway set and I have two emissive planes closer to my characters (0.000001 opacity)... usually mesh lights give me waaaay better times than photometric lights.

KindredArts

I take it you're using an HDRI? You don't necessarily have to wait for the render to finish, even a finished render can have some noise. I started using iray with a 970 and even though it took a while, never a day. Are you using optix acceleration?

There isnt much you can do to speed things up now it's rendering, i'd say cancel the render when it looks ok. You can use a bit of noise reduction after that to clear up any remaining grain.

Steven-V

For some reason, turning the lights in some scenes, like the ones in the Parkland High, into emitters just destroys render times in Iray. I don't know why, but I had it happen to me.  Putting a primitive plane of the same size and shape and turning it into an emitter with exactly the same luminosity values, for whatever reason, renders much faster. You might want to try that.

EDIT: Also reflective surfaces brutalize render times. I had a floor that I did a simple Iray convert and was very reflective as a result. Render times were 3-4 hours. I noticed that with a similar scene, another floor non-reflective, render times ~ 1 hour, maybe a little less.  I changed the first scene to give the floor non-reflectiveness like the 2nd scene, and render time dropped... not to an hour but to about 1.5 hrs... much faster.

In particular, indoors + reflective + emitters or point lights = death for rendering.  Outdoors with sun/sky or HDRI, for whatever reason, reflectiveness is no problem.

sincartier

The more you know!

Anyways, I canceled the render after about 18 hours and 22% done.  I do try to use emissive planes when I can, I did notice an enormous difference in render times.  I just didn't figure this one would take so long since I've had much much more complex scenes that only took about 4 hours to render.

Tobor

The reasons for slow renders when using emissive objects (especially with non-planar geometry), indirect light, low light, infinite ray bounces, and other aspects have been well explained in many posts. Rather than repeat the details here, do a Google search into the forum. "Slow render Iray" is a good search phrase. Among the suggestions are:

* Avoid meshes for emitters unless they are props in the scene, and even then, keep their geometry simple. The more polygons, the higher the number of ray path calculations, as the light rays must be calculated for each polygon, even if it's a small object.

* Use HDRi for general lighting, and rely on the primitime light types (spot/area, point, and distant) as much as possible. Remember that spot and point lights can be made to emit a more diffiuse light by enlarging their emitters, and that the luminosity of distant lights are calculated as illumination at the scene, not from the light itself. Therefore, VERY low values of 8-10 are appropriate; this means 8 to 10 lumens per square centimeter of light, as measured at the scene.

* Avoid using only indirect light, but if it can't be helped, try turning on the Architectural Sampler filter. It's designed to help in these instances, though the amount it helps depends on many factors.

* Avoid too little light. The more light, the faster the convergence estimate calculations. Convergence is when the same pixel receives many simular ray hits, enough that Iray has a good idea the result at that pixel is accurate. Too low of light = not enough "photons" to make this calculation.

* Shiny surfaces and objects add ray traces. You can make surfaces diffuse, and/or lower the Max Path Length. The default -1 means "unlimited." A value of 8-10 can yield realistic reflections while trimming render times.

 

Steven-V

Great advice, Tobor!