Glass shader weirdness

[dduane]

Hi there folks --

Got a question. I've been working on a render for an upcoming book cover and something a little odd seems to be going on with the glass shader. Doubtless I've got something set wrong: just curious if anyone has (a) seen this problem before and (b) can suggest a fix.

The scene at the moment consists of a planet with a sphere positioned in front of it, and a glass shader applied to the sphere. The sphere is an imported .obj file: I too ran into the problems with procedural cubes and spheres that j meyer reproduced here (http://www.planetside.co.uk/forums/index.php/topic,19442.msg191113.html#msg191113), so the import seemed the simplest way to get around the issue for the moment.

Here's a crop of the area with both the planet and the sphere. (The complete .tgd file is attached at the end of the post.)(Assuming I can remember how to use the markup, it's been a while since I've done this...) 

[attach=1]

It looks to me as if the area behind the sphere has rendered at a lower quality than the rest of the image (which at the time was set for .8).  Does anyone know why this might happen? Any thoughts on how to get it to render at a quality more like that of the rest of the image? Double-sided surface has been checked on this object, but nothing else has been altered from the default settings except for the decay tint, just a little.

Thanks in advance for any help anyone can come up with. :)

Best -- Diane

[attachurl=2]

[yossam]

You can see the tri's in your object, I would try subdivision on your object first. 

[RArcher]

I believe the lower quality behind the sphere can be fixed by going into the internal network of the "render node" and then the "Render subdiv settings" node and changing the "Ray Detail Multiplier" setting from 0.25 to 1.  This will really slow down render time though so you may want to crop down to just the area that needs fixing.

[archonforest]

I had the same problem and when I cranked up the ray multiplier to 1 it was good.

[Hannes]

Agree. Did exactly the same yesterday.

[dduane]

Well, unfortunately changing the subdiv settings doesn't seem to have done anything in particular. With the ray detail multiplier kicked up to 1, the images are indistinguishable as far as I can tell:

[attach=1]

They were so indistinguishable that I ran the render a couple more times in quick render (half the full render image size) and turned "ray trace objects" off and on to see if it made any difference. Nada.

...Unfortunately the "render subdiv settings" page at the wiki lacks any data as to what the max setting for the slider might be, so (admittedly not knowing if there was any point) I pushed it up as far as 5 and still saw no difference.

Does anyone have other thoughts on what settings I might want to look at changing? Something with the normals, perhaps? I confess I was expecting this to work, and was surprised when it didn't.  -- D.

[Hetzen]

Looks like your object has smoothing switched off. That's why it looks and renders its diffraction like a disco ball.

Try turning on smoothing then re-export your sphere object.

[dduane]

Hmm, thanks for that! Unfortunately I didn't create the object myself, just snagged it off the web: I'll have to go looking for one with better smoothing.

Let's let this sit until tomorrow and I'll have time to find an appropriate sphere object and take another run at this. (ETA: Or download Blender.)  ...As I'm presently also working on the short novel that's meant to go with the cover -- the third of the three works referred to in the rough image below -- and the deadline's getting closer...   

Thanks for the help, all! -- DD

[attach=1]

[Hannes]

Although Allen was faster, I'll post mine as well. It's already TGO. Just made it in 3ds max.

[dduane]

Allen, Hannes, thanks so much! You're both very kind.

I'll give both the files a shot. Much appreciated! Thanks again.

[bobbystahr]

If the sphere is a closed surface don't you turn Double sided off? The way I understood it double sided was for things like flat 1 pixel thik window panes and the like.

[archonforest]

There is a sphere object in TG already. Did u tried that before looking one on the net?

[dduane]

So, an overnight progress report:

First of all, thanks very much to Hetzen for catching the source of the problem I was having (the sphere object with its smoothing turned off), and thanks again to Hannes and allen1 for the sphere objects they kindly posted for me to download. (allen1, I have to try yours again; the remote site was insisting that my version of Firefox was out of date and wouldn't let me download... Seems unlikely, but whatever, I'll check Firefox and try it again.) After ten hours of rendering (boy howdy does setting the ray detail multiplier to 1 slow things down) the smoothed sphere object is about 90% rendered and looks fine, so that problem is solved. (I note the highlight left over from the otherwise-invisible sunlight light source, but will probably just touch that out in Corel.)

[attach=1]

Next on the list: sticking a camera inside the object, projecting a heads-up display on the inside of it, and then adding the human figures who're examining the display.

Bobbystahr: yeah, I know that leaving "double-sided object" unchecked is more usually the way with the glass shader. But when I tried leaving it unchecked with a sphere, I got an effect more like a crystal ball than a bubble -- i.e., everything behind it inverted. The bubble was what I was after: checking "double-sided" gave me that. I had a brief flirtation with trying to get the same effect using the water shader, but after a few tries the glass shader was much closer to what I wanted.

Which immediately brought me to the next problem. Archenforest, yes, when I started work on this idea the first thing I reached for was Terragen's native procedural sphere. But unfortunately that seems to be acting strangely with the glass shader when "double-sided object" is checked -- see this post for j myers' image that illustrates the problem (look at the second and third examples in the middle row of his image):

http://www.planetside.co.uk/forums/index.php/topic,19442.msg191113.html#msg191113

Importing a sphere object from elsewhere solves this problem (as in the first image in the middle row), so that's what I wound up doing. Matt suggested he was going to look into this issue, but he doubtless has a zillion other/more important things on his plate. For the moment I'm happy to think of this as an "undocumented feature" and move on. 

So thanks again, everybody, for the help! I'll post a full version of the finished render here when it's finally done. Next week sometime, most likely. (And will wail piteously for help if anything comes up between now and then.)    -- DD

(ETA: to allen1, re a writer being here: Thanks! I loved Terragen for a long time before I realized, in one of those sudden "rushes of brains to the head", that you could do book covers with it. Haven't looked back since.)

[bobbystahr]

Gotcha dduane, and congrats on solving it..gonna be a very cool cover.

[archonforest]

Can u post the settings for the glass shader u finally used? I try to reproduce the picture u got but no luck so far.