Art of Rendering (?)

[Puppet]

Some phrase of Bart from article Art of Rendering

To handle moving objects, one Final Gather file per frame is processed in a first pass. When the beauty pass is rendered, Final Gather points are interpolated across multiple frames to “smooth out” the solution.

Bart, please explain what you mean.
Is it possible interpolete some fg files from different frames?
Thanks.

[Remydrh]

Yes, in fact it is exposed in 3ds Max but not Maya. ("Interpolate over N frames" seen here)

4907421666_45b9a0c028.jpg

finalgather file [ "name1", "name2", … ]
mental ray supports to attach a list of finalgather file names instead of providing just a single file name. All files are read and merged. The first file is rewritten with the complete map like in the single-file case.

In Maya you can provide individual files and it will merge them but the process of going to the next frame is not automatic.

We've actually found the fgshooter shader very useful for eliminating variance without the step of generating FG Files.

[bart]

Caveat: Remember that what I talk about may or may not be integrated for easy use.

Any given frame can contain multiple fg map files. Each fg map contains fg points generated at various times within the open shutter interval. So interpolation could use points generated from qmc spread times across several frames.

Now if you preprocess a shot every frame for example naming shot.0001.fgmap, shot.0002.fgmap, etc.. then you could reuse those fgmaps in a time window surrounding the current frame being rendered. For example, with a three frame window, you could use 0001, 0002, 0003 for frame 2, or for a five frame window, 0002, 0003, 0004, 0005, 0006 for frame 4.

And because the fg maps use the open shutter interval for fg point creation times, you could micro optimize and set your shutter to 360 degrees during the fg map only creation run, and set it back to 144 dgrees when re-using them and rendering the frame.

Now Maya offers multiple FG map slots per frame, but the naming system doesn't help you to do this very easily.

Also note that you can take objects in and out of FG maps, so you could combine FG maps with different subsets of objects. That definitely has not been explored enough for production optimization. Imagine putting all statically lit objects in a single FG map, and then only using dynamically lit object FG maps for multiple map interpolation.

That is a lot of work, but hopefully helps you understand the possibilities. Now lets talk about hopefully easier to use solutions.

There is a shader named mip_fgshooter that can be used to take all the fg points from several cameras each frame. It is integrated into 3ds max. As for Maya, Brenton Rayner has written a script to make it easier to use inside of Maya. See here: http://elementalray.wordpress.com/category/scripts/

In the case of using several frames before and after, use the offset cameras in that UI.

Its worth reading his post even if just to visualize the camera setups to understand how to use whatever mechanism you wish to use.

[Puppet]

I know about merging of fgmaps, but it's not interpolation between frames. It's just merging

So frame interpolation is only mip_fgshooter feature.

Thanks.

[bart]

If you separate fg map creation phase creating a map per frame, then you can reuse them for rendering later where several different frame times can be interpolated with the different fg maps. That is what I meant. We had proposed it a long time ago for integration, and obviously, it was not picked up.