things get dark when lake is turned on

[oysteroid]

I described in a thread in the support forum how I've been plagued with weird issues with things going dark for no apparent reason. I solved the problem of the artefacts that I was mostly concerned with there. But yet again, a darkness problem has returned.

This is just weird. I am testing some different wave settings on my lake and everything is fine. Suddenly, out of nowhere, my rocks in my crop render are very dark. I changed nothing. After doing some experimenting, I find that if I turn my lake off, the enviro light on the rocks is fine. Turn the lake on, and they are dark again, without changing any other settings. Here:

[attachimg=1]
[attachimg=2]

The difference between the images sizes is only because I was quick and sloppy with my PS crops of the TG render output of each image.

This is in each case the same view with everything the same except the lake is enabled in the first and disable in the second. What the heck?!! This kind of thing is driving me mad! I think I've got gremlins!

I have the water surface displaced. But detaching the displacement nodes doesn't get rid of the problem. I even deleted my lake and water shader nodes and created some new ones with default settings. Same problem.

Any ideas?

[TheBadger]

I think I've got gremlins!

That is the likely cause, imo. What you want to do is smash your PC then set it on fire. Because if you wait for the "correct fix", then the gremlins will just read it and play along, tricking you into thinking you have fixed the problem when you really haven't.
http://www.free-wallpaper-download.com/movie/gremlins/gremlinsII4.jpg

[oysteroid]

Badger, I'm tempted to set my computer on fire, believe me! 


Things get weirder...

I went back after that post and rendered again and things are fine with the lake on. The rocks are lit by the enviro light. I render again without changing any settings at all and they go dark again. Render again, light. Render again, dark. Render again, dark. Render again, light. And so on, like flipping a coin. It is totally random. So I shot a video since I thought some might doubt what I am saying, thinking that I surely must be changing a setting somewhere. Here it is:

http://youtu.be/02kmbvN-cBI

This intermittent darkening does not happen with the lake turned off.

I think I am going to run some memory and processor diagnostics just in case...

[Dune]

Do you use any displacement intersection? And is there no sun, just enviro light? No mountain throwing a shadow just across the pebbled area, which is calculated differently with every render by GI?

Just guessing, but it's weird. How about putting your tgd up here?

[oysteroid]

Dune, I am not sure what you mean by displacement intersection. So I don't think so. And there is a sun. The rocks are just in a shaded area. The sun is low on the left and the rocks and water are down in a depression. So there is a shadow across the pebbled area. Would the shaded area be calculated differently every time by GI, and only when the lake is enabled? It seems like with some of these issues I am having that something to do with GI is the source of the problem. And all my GI settings while doing these tests are the default ones.

Sharing the file is a bit of a problem. It has all sorts of stuff that goes with it that is too big to upload, such as the vector displacement (4096x4096 EXR) that makes the depression where the rock bed is, some OBJs, and so on. There is also a secret in there! 

I think that in the morning, I am going to try recreating the file. I had a problem like this before with this scene where my waterfall was black in the shaded area intermittently. Rebuilding the file by creating a new file and bringing my main nodes in with clips files seemed to fix it.

All these problems I am having might just keep me from making the deadline for the contest! *sigh*

I ran processor and memory diagnostics and all was fine.

[Dune]

Then I wouldn't really know, though you could send the secret to me personally 

What if you replace the lake by a plane (turn shadows off), or a sphere (ditto)?

[Upon Infinity]

Increase your GI cache detail in the GI settings of the render shader.  This will fix your problem.

[oysteroid]

Thanks for the suggestions, Dune!

Upon Infinity, that seems to work! What the heck? Why does it do that?

Thanks! What would I do without you guys? The amount of help a person new to Terragen needs is seemingly limitless! And you guys are very helpful! Without these forums, I think this software would be almost unusable!  ... for slower ones like me anyway!

[Oshyan]

The GI process is pseudo-random and can vary between renders. Usually the variations are minor, but in certain cases they can be more noticeable like this. Lower GI settings are less accurate and therefore more prone to large fluctuations in the randomness. If you're not making changes that affect the GI, you can also just generate a GI cache to work off of for a bit. Just don't forget to re-generate the cache if you make any GI-affecting changes!

- Oshyan

[oysteroid]

Thanks! I'll try that in the future.

By the way, I took that video down. It wasn't publicly listed anyway. I just had to upload it and show that I wasn't out of my mind!

[Oshyan]

Yes, it was definitely good to see it. Thanks for posting it, at least temporarily. You're *not* crazy.

- Oshyan