Creating the Light Volume

This section covers the creation of the lights volume and configuration of it's pass.

Theory

As our volumetric caustics pass only displays volumetric light once it has begun to
interact with our sphere and cylinder we must now create a pass which shows the
volumetric light up until it begins interaction with the sphere and cylinder.

Preparing the Pass

All the work we have to do for this section is working with a second pass. To start off
with switch to the render menu then create a new pass by clicking
Pass->Edit->New Pass->Empty .

Now create a new partition by selecting Pass->Partition->New. Now go to your explorer
and change it to passes. You may wish to rename this pass to Background_Pass.
Make sure you change your current pass to this one in the dropdown under pass in the
render menu.

Now expand your background_objects_partition and move all objects except your
caustic volumetric geometry to the new partition.

Click on the background_objects_partition icon and change it's render visibility to hide
members.

If your scene has more lights then just the volumetric one then create another partition
and shift those lights there.

Now select the background_lights_partition and choose Get->Property->Volumic.

Now check the boxes for force volume shadows and transparent. Tweak all the other
settings as desired. They're left as defaults in this tutorial.

Render Options

Choose render->options and configure your render options as desired. This time make
sure you've switched off caustics.

A test render should look something like below.

Compositing

Ok you're ready for the final step - compositing the final image.