From: Dave Lajoie

Subject: Rendermap and Final Gathering: few techniques...

Hello Guys!

I have been investigating this for few customers and I thought I would share

this with you.

The question:

When a render a scene with FG and then bake the result using rendermap,

the FG doesn't look the same

why?

As you may know already, FG will only cache fg samples for visible surfaces

( visible from the camera )

since the rendermap uses is a virtual camera to render the surface to an

image file,

The FG requires some handling to make it work.

Here are few workarounds to solve this problem:

1) Use render region to build a FGmap, which will then be re-used in the

render pass

options during the rendermap process

a) in the render region, enable FG, give FGmap a brand new name ( to ensure

there is no old file around )

make sure to mark rebuilt off. This will allow MR to increase FGmap each

time the camera is being moved.

b) define a region and orbit the camera around the object or inside the

scenery such that camera sees at least once each surfaces. This requires to

be done manually

c) Once the FGmap accumulation process is done, you turn off render region

d) you go to the render options of the active pass, and set the FGmap to

point to the file you just created.

Make sure to turn off rebuilt since you don't want rendermap to erase it ;)

The FG settings in the pass should be identical to the ones set in the

region options.

if it is not the same, it is possible MR cast few extra Fg samples during

the lightmap and rendermap process which

would then be added to the fgmap. I also suggest to lock the fgmap file, if

you plan to rendermap again later.

e) start rendermap process and enjoy the show.

2) The method above is rather hard to script and automate since you need to

use the camera to paint the FGmap file and accumulate the fg samples. The

other approach is to increase the FG accuracy really really really high,

like 6000 and force it to rebuilt each time. The radius should be around 1

to 100, depending on the objects and its surroundings.

if you plan to use OGL to display the rendermap result, ensure to set the

OGL image resolution to the rendermap resolution used. otherwise some

interpolation problems will occurs and this will cause black borders to show

up.

I hope this helps you to cook down really neat FG scenery and speed up

rendering :)

Dave.