I hesitate to call this a bug, but the glass shader I set up in 2.78c isn’t rendering as transparent in 2.79 RC1. I made no changes in the file, just loaded it into 2.78c and rendered, then did the same in 2.79 RC1. Here are the renders and the node set-up:
Anyone else having this problem? Has the glass shader changed between versions? Or this is some kind of side effect of the new faster, less noisy rendering?
It would seem so.
2.79 has got some more settings, among which there is ‘AO Bounces’ that is what fails here; if you set it above 1 it works correctly, but I don’t get why AO should matter for transmission.
EDIT: sorry, I’m speaking of Simplify setting here.
Thanks for clearing that up, Paolo. Should I report this as a bug? I guess the real question in my mind now is: is it a bug in 2.79 or 2.78c? And if it’s 2.78c, should we assume it’s been fixed and if that’s the case, is it worth reporting at all?
It matters because what the simplify setting is doing is changing any bounce after X into an AO bounce.
Hence if you set it to 1 - you get one diffuse/glossy/transparent bounce, then bounces 2, 3 etc are AO bounces. You need at least 2 bounces for a transparent object to appear transparent.
When using the simplify settings - I always set it to at least 2 (and usually 3) in order to get sufficient bounces for transparency and glossy surfaces to appear fairly accurate.
Also remember that the simplify panel has separate setting for viewport and F12 rendering - so you can have 2 bounces for viewport rendering to give you a fast viewport render - but then 5 bounces for a full F12 render which will be slower but more accurate.
This is not a bug - the simplify function is working exactly as intended.
Thanks moony for your explanation,
I’m not versed on Cycles, so it’s not even much clear to me what AO exactly is in Cycles; always I think to AO as something of subtractive, and I will never make any use of it other that for single materials aged effect and alike.
To me the name of the setting is quite misleading anyway, but maybe it’s the use of the term AO itself to be inconsistent.
If you hover over the AO bounces box - you get a tool tip explaining what it’s doing.
Essentially when it gets to the specified number of bounces - it replaces the full path tracing indirect lighting calculations with a simpler indirect lighting and a tinted ambient occlusion contribution.
So if you set the value to 1 - the entire scene is treated as direct lit and all of the indirect lighting is handled using this simplified “AO” approach.
If you set the number of bounces higher - you get more contribution from full path tracing and less from AO (but then it takes longer).
You can actually get similar results by turning off Simplify, setting Light Paths on the render panel to “Direct lighting” and then turn ambient occlusion on, on the world panel and set it’s value to around 0.2. This method however doesn’t tint the AO like the simplfy setting does - so doesn’t look as realistic.