mr 3.9 and tiled exr and map renderimtes

[haggi]

Hi,

mr 3.9 should be able to read tiled exr and use it the same way as the native map files, is that correct?

If yes, then my tests show that there is no difference at all if I use tiled exr or non tiled. I checked the exr files with the exrheader tool from exr tools. It shows that one version of my exr has no tiling information the other has tiles. Both renderings needs the same amount of memory an time.

The reason why I want to try tiled exr instead of map files is that the finalgather pass with map files takes up to 8 times longer than without map files. So maybe anyone can answer my questions:

- are tiled exr supported for caching?
- any idea why fg pass with map files takes so long? Is it because so much lookups are necessary for hemispherical fg sampling?

[juri]

Hi Haggi,

If you are using standalone, --message img files -- on the command line would print for each texture which technique (caching, memory mapping for .map or loading the complete file) is used. I'd bet that in your case both EXR files are just loaded.

Tiled .exr file can be cached or loaded. However, by default they are only cached if the texture is declared "local". Identical time/memory suggests that "local" qualifier is missing and the complete image file is loaded.

(Note: .map files are always treated as local textures.)

In principle, texture caching is slower on access than in-memory images, which could lead to a significant slowdown if the rendering is bound to texture lookups. The advantage of texture caching is the ability to render much larger scenes with texture size exceeding the machine physical memory.

In 3.9, it is possible to switch texture cache mode off (-texture cache on/off/local command line option or {_MI_REG_TEXTURE_CACHE} registry with value "on"/"off"/"local".
Local means that only local textures are cached, this is the default.
I.e., if you have map files, you could try -texture_cache off to check if it makes things faster.

Hope this helps,
Juri

[haggi]

Thanks Juri thats good to know. Unfortunatly I'm not using the standalone but maya for rendering so I fear I cannot simply add a local qualifier for my exr files. Maybe there is a way to do so.

We solved the slowdown by simply using a rayswitch node with a low resolution texture for finalgather rays, works great.

[Remydrh]

Hi Juri, correct me if I'm wrong, but can I use the registry entry in the rayrc file for Maya? I thought you could do that but not sure if that is old information.

[juri]

There is maya.rayrc file under Maya/mentalray.

For adding local attribute: Steve has posted a way to add it for a single texture here:
http://forum.mentalimages.com/showthread.php?8083-Force-local-textures-with-geo-shader

Juri

[haggi]

Thanks, works fine.

I could read in the exr docs that we have the possibility to create mipmaps and ripmaps, where ripmaps seems to create more different levels. Following the exr docs this can speedup the anisotropic filtering during texture lookups. Are there any suggestions which one to use with mentalray?

[bnrayner]

I believe you can add the local attribute to any Maya "file" node since it is just a wrapper around a mental ray texture anyways.:

import pymel.core as pm
pm.addAttr("file1", ln="miLocal", at="bool")