Rendering - empty areas problem

[ccb]

I have had several occasions when TG2 is rendering that there are one or two miscellaneous large black squares that aren't rendered.  I have learned how to get around it - I render in sections and then everything renders.  But I wonder if others have had this happen and why?  It doesn't seem to have any relationship to objects in the scene.
Christina

[cyphyr]

Mostly this happens with very high render and/or atmosphere/cloud settings, try lowering them ...
Richard

[Tangled-Universe]

This is very likely related to memory issues. That's also why rendering in sections works out for you, because this way you're reducing RAM-requirements.

To avoid this you either have to:
reduce GI settings
reduce atmosphere/cloud-samples. For clouds; try to avoid a detail level >1.
reduce render-resolution
reduce number of objects or rendering with lower AA

[ccb]

Thanks to both of  you.  The times that happened were with pictures with a lot of atmosphere.  I'll keep that in mind and try not to push all the settings to their highest.
Christina

[Tangled-Universe]

You're welcome.
You may also find this link useful:
http://forums.planetside.co.uk/index.php?topic=6442.0

[ccb]

Thanks so much - I remember seeing a long time ago a post, probably that one, about not pushing all the settings to the highest.  I guess I succumbed to temptation!  I'll print those out for future reference.

[Oshyan]

Another good and commonly missed approach to fixing this problem is to try smaller (or even default!) render cache sizes. Some people increasing the cache size a great deal, no doubt assuming it will give them a big speed or quality boost. It does neither, though it *can* increase performance a certain amount in some cases.

Generally speaking 100MB cache *per thread* is sufficient. 200MB/thread can give some performance benefits; beyond that there is little advantage. So if you have increased your cache size, reduce it back to 100MB/thread (e.g. with 4 threads the total cache sizes would be 400MB). You can also try 50MB/thread, though this can reduce performance somewhat. But still a completed render with no undrendered areas and slightly longer render time is probably preferable to a faster render that misses spots.

- Oshyan

[Henry Blewer]

Terragen 2 defaults to 400 MB on my machine. Would changing this to 100 MB help? I do not often have memory issues. I am more interested if a smaller cache would speed up the render time.

Pentium 4 HT
4 GB Ram
6 GB swap size

[ccb]

I finally finished my picture by dividing it into 5 parts!  One thing I noticed on the suggestions about rendering in the link above is that it says to avoid setting the qualities high, but I saw that the qualities said to be very high are higher than the slider goes.  I guess it is possible to type in higher numbers but I thought the slider gave you the highest number.  So I haven't been going above what the slider goes to.
Christina

[Oshyan]

Reducing render cache size below 100MB/thread shouldn't be done unless you have a memory limitation (you're getting errors or crashes like the one seen above in this thread). Using cache sizes below 100MB/thread will tend to reduce performance, not improve it. Larger cache sizes can improve performance, but the difference is often not significant, and usually conserving memory is more important, hence the default of 100MB/thread. If you're using less than 4 render threads you can reduce the render cache total size to achieve 100MB/thread again if you do want to save memory (e.g. 2 render threads would use a 200MB cache).

- Oshyan

[Dune]

I guess it is possible to type in higher numbers but I thought the slider gave you the highest number.  So I haven't been going above what the slider goes to.

You're right; you can type in any number, even negative ones. Everywhere. Nice to experiment with, and you might get some weird and interesting results. For instance in the merge shader, set merging to a negative number and one will 'dive'.

[Henry Blewer]

Thanks Oshyan. I did a partial render while at work last night which used a 200 MB cache. The result was less RAM usage. I am going to reduce the Swap file size. (T2 likes to use the swap file on my system) This should give me a speed boost.

I wonder if I can force the swap file onto a flash drive... USB is slow, but better than using the hard drive.

[Oshyan]

USB speed shouldn't be better than using a modern, reasonably fast HD...

- Oshyan