PDA

View Full Version : Black squares appearing in the render



rsfurr
02-25-2005, 03:07 PM
I've been having trouble with 8.2 when rendering (version 8.2, on a dual G5 2.5ghz Mac, running 10.3.8). Black squares appear in the render for no readily apparent reason. The effect is stronger with higher antialiasing levels, and seems to be affected by adaptive sampling. The following images are from a scene I built as an example for the 3D class I teach, but it seems to happen in every render. Any ideas as to what's going on?

Activator
06-08-2005, 06:07 AM
I am having a MAJOR problem with those little black squares!

My testing and research has traced it to a combination of Volumetric lights WITH shadows turned on, high antialiasing AND very high Motion Blur (ie: @300+)

Other folks have found that double-sided textures and some procedurals can cause this.

Right now, I'm trying to render a sequence that has two Volumetric lights, one is creating a swirling smoke/fog atmosphere, the other is positioned behind a 3D logo, backlighting and casting light "rays" into the smoke/fog.

If I turn shadows OFF on the 2nd (backlight) light, the problem goes away, but then the scene doesn't look the way I want it to look! I thought I had it solved by making all textures single-sided and creating double-sided polygons for those surfaces that need it, but the latest test reveals that the black squares are back.

Anyone with more ideas, please post ASAP!

Thanks in advance.

toby
06-08-2005, 09:24 PM
I can't repeat the problem, but it sounds like a bug anyway - a workaround may be to use shadow maps instead of ray-tracing. Might render a lot faster too.

I don't suppose you're rendering BRDF and raytrace reflection at the same time, are you? That's a known bug causing black artifacts.

Activator
06-09-2005, 06:12 AM
Toby-

Not using BDRF shaders. Just plain-jane surfaces and one UV textured surface. (The squares occur on both types of surfaces.) All surfaces are single-sided textures. All polys are single-sided except the UV textured object, which has double-sided polys.

I can see that, while the render is creating it's multi-pass (AA), there are "lighter" squares in the mid-areas of some shadows that "turn" black on the final AA pass.

I "think" I've solved it by settting the backlight/volumetric light to use Shadowmap shadows WITH "Cache Shadowmap" turned ON. (Tried that before without "cache" on and got the same black squares.)

I'm rendering the sequence now and it "seems" to be fine. (In 23 hours, I'll know for sure!)

One more caveat, I rendered this exact scene (the SAME file with a few tweaks in the camera move) a few months ago. At that time I was running LW 8.2. The ONLY difference now is that I'm using LW 8.3!! So it's gotta be a "new" bug.

I don't have time to re-install LW 8.2 to test and, I would put up the scene file for you to check out, but I can't. It's an FX sequence for a feature film, and I can't release anything until the movie is out.

Thanks for your thoughts.

Activator
06-09-2005, 10:16 AM
OK... it's TOTALLY because of having raytraced shadows selected for the 2nd volumetric backlight.

No matter what I do, how much AA, motion blur, etc., if the 2nd volumetric backlight has raytraced shadows, then black squares show up in the mid-shadow areas.

Once again, the scene has two volumetric lights, one main distant light which is making the whole scene foggy/smoky, and a 2nd volumetric light which is backlighting a logo. The logo uses "normal" metallic and semi-reflecctive texturing, nothing fancy, no plugins. The logo uses single-sided textures and polygons. Raytracing for shadows, reflection and transparency is on. (The logo goes transparent at one point)

The black squares show up in the mid-shadow area when raytraced shadows is on for the 2nd light (backlight). It goes away when switched to shadow mapped shadows.

Unfortunately, I cannot post stills due to the nature of the project.

toby
06-09-2005, 01:11 PM
Funny, the guy who started this thread is using 8.2 - maybe he's using BRDF -

marinello2003
06-10-2005, 09:10 AM
I got black dots when overlapping lens flares in 8.2. However I have not seen similar problems with 8.3 since (MAC).

Have you tried rendering the same scene in F-Prime?

Activator
06-10-2005, 09:52 AM
I'm 100% certain it's to do with the raytraced shadows of the 2nd volumetric light.

I'm rendering the scene now after changing the 2nd Vlight to shadow mapped shadows, and there's nary a black square... even at extreme AA and extreme (500) motion blur.

I rendered this EXACT scene a few months ago using LW 8.2 WITH raytraced shadows on the 2nd Vlight and had NO trouble, so it's a new bug in 8.3 (Mac).

I guess the combining of 2 Vlights in my scene "could" be part of the cause... the 1st light is still using raytraced shadows so, maybe two Vlights using raytraced shadows is the trigger for the bug?

papou
06-12-2005, 01:21 PM
ok, i'm having this f%#!g black squares in my render!!

I'm using the volumetrics HD_Instance plugin so the bug surely come from lightwave volumetrics engine. im using 8.3

black dots appears on the volumetrics and heavy black square in the volumetric's reflection.

I'm using motionblur 50%, no doubleside. Some lights are raytraced.

To me the problem is due to Multithreading. black square don't appear with 1 thread.
Could you confirm that?

one more thing i would like to clarify

I'm rendering with screamernet.
I know i have to launch 2 nodes if my system is multithreaded cause LWSN is monoprocessor.
But if my scene is saved with more than 1 thread. 1 cpu is rendering more slowly that the second. I mean, it wait the cpu 1.
So Did we have to manually select 1 thread?! I was thinking that it was automatic because LWSN cannot handle more that 1 cpu...

With my black squared scene, if i save it with 8 thread per example, LWSN is rendering black square.

I'm really really tired about all of that.

I have to manually find black squared frames into 5000 frames!!

i lost my render, my weekend, my client.

Are we beta-tester?

papou
06-12-2005, 01:28 PM
Ah, and for sure, i'm not using New AA algo.
And for sure i'm not using Adaptive sampling.
And, Toby, i'm not using BRDF.
marinello2003, there is no volumetrics compatibily with Fprime, so no way to test that bug.

toby
06-12-2005, 01:45 PM
ok, i'm having this f%#!g black squares in my render!!

I'm using the volumetrics HD_Instance plugin so the bug surely come from lightwave volumetrics engine. im using 8.3

black dots appears on the volumetrics and heavy black square in the volumetric's reflection.

I'm using motionblur 50%, no doubleside. Some lights are raytraced.

To me the problem is due to Multithreading. black square don't appear with 1 thread.
Could you confirm that?

one more thing i would like to clarify

I'm rendering with screamernet.
I know i have to launch 2 nodes if my system is multithreaded cause LWSN is monoprocessor.
But if my scene is saved with more than 1 thread. 1 cpu is rendering more slowly that the second. I mean, it wait the cpu 1.
So Did we have to manually select 1 thread?! I was thinking that it was automatic because LWSN cannot handle more that 1 cpu...

With my black squared scene, if i save it with 8 thread per example, LWSN is rendering black square.

I'm really really tired about all of that.

I have to manually find black squared frames into 5000 frames!!

i lost my render, my weekend, my client.

Are we beta-tester?

Yes, your scene saves the number of threads, I remember hearing that you should set the scene to 1 thread for Screamernet, and that it renders faster too.

It would be great if that solved the black square problem! Can you try it Activator?

Activator
06-12-2005, 02:22 PM
Yes, your scene saves the number of threads, I remember hearing that you should set the scene to 1 thread for Screamernet, and that it renders faster too.

It would be great if that solved the black square problem! Can you try it Activator?

I WAS rendering with one thread when I was getting the black squares. I am 100 percent convinced it's an 8.3 bug that has to do with raytraced shadows and volumetric lights. I have rendered about 8 different passes of the scene that was giving me trouble, and since switching the 2nd Vlight to shadow mapped shadows, NO MORE black squares!

BTW, I use Bruce Rayne's "Renderfarm Commander" with one thread per CPU. It's amazing that, on a Dual 2.5 G5, a frame will render in 16 minutes with 4 threads (F9 render), and with Renderfarm Commander using two LWSN instances, each set to 1 thread, TWO frames will render in the SAME 16 minutes! I have two dual CPU G5's, so I get effectively 4x the render speed with Renderfarm Commander!

papou
06-12-2005, 02:45 PM
I don't think any actual screamernet controller can accelerate rendertimes.
I think your scene is rendering on your workstation in 16min with 1 thread.
If your system is bi-cpu, your rendering times must be something like half the times with 2 thread.
With 4 thread, it can be longer. Same as 8 thread.
I have experimented faster volumetric render with 1 thread on my bipro workstation. Depend of the scene, depend of how much volumetrics covered your frame...
The only person who can explain that very well is Gregory Duquesne, but he is busy and don't care about us. in fact, who care about us...
All of this is OT.