View Full Version : Mental Ray renders slow to start

08 August 2009, 11:58 AM
Hi people. I have a really annoying issue with my scene.

When I render with Mental Ray the scene takes about 5 minutes to even start rendering! I assume this has something to do with the way Maya talks to Mental Ray. When I render with Maya Software it starts straight away. Any ideas on how to speed up the mental ray renders?

I am using Maya 8.5 and the scene has about 500,000 polys. A lot of the geometry consists of instances.


08 August 2009, 02:06 PM
Might help to convert your Textures to *.map files if you have a lot of them.

08 August 2009, 03:09 PM
I have the same issue happen and I use .map files. As long as it renders, I can wait a few seconds. Just dont crash on me!!!

08 August 2009, 03:29 PM
Are your models in the subD preview mode (3key)?

08 August 2009, 07:17 PM
- Increase the verbosity to learn more

- run Render>Run Render Diagnostic

- do you use fur ?

- is it computing GI ? Depth map shadows ?


There could be a lot going on.

08 August 2009, 07:21 PM
POst setting please. Your geometry is good geometry?

08 August 2009, 11:49 PM
Thanks for the responses guys.

My scene consists completely of polys. Ray traced shadows are on, no depth map shadows, no GI, FG, fur etc. As far as interesting things like that go, I've kept it to a minimum.

The geometry is 'good' as far as I can tell, i.e. it's mostly 4 sided (some tris) and all faces are planar.

Most of the materials are simple Maya materials (blinn and lambert) with no textures.

Does Mental Ray read Maya instances the way it should (i.e. load the one piece of geometry for all instances)?

08 August 2009, 12:30 AM
Okay, I set verbosity to 6 and ran render diagnostics. While there were a bunch of errors (convert texture to .map file for instance) I don't believe this to be the cause. The textures are elsewhere in the scene and when I remove the heavy piece of geometry with no textures, it renders quickly.

I also re-rendered the scene and this line appeared in the script editor:

// Info (Mayatomr.Script): computed memory limit: 1027 //

Could this be the route of my problems?

By the way, numbers 1-3 for subdiv levels don't work in 8.5 so this can't be the problem either.

08 August 2009, 02:09 AM

The trick:

Maya Render Globals > Translation > tick boxes for:

"Export Exact Hierarchy"
Maya help on the issue:

Export Exact Hierarchy
Tries to preserve the DAG hierarchy during processing. This produces additional mental ray instgroup entities. There are certain unresolved material inheritance issues in this mode, but it works well in the general case. Deeply nested DAG hierarchies may be translated much faster compared to the standard Maya iterator mode that always flattens the DAG. Default is off.

So it wasn't that the scene was too heavy, it was that my scene had deeply nested objects (I think most things were parented, then grouped, grouped again and grouped again for good measure). I thought I was being organised, turns out I was killing speedy render times.

08 August 2009, 12:26 PM
Well; thanks for that. Never heard of it.

CGTalk Moderation
08 August 2009, 12:26 PM
This thread has been automatically closed as it remained inactive for 12 months. If you wish to continue the discussion, please create a new thread in the appropriate forum.