Overview
This tutorial is part of a guide that walks you through the process of importing and rendering Houdini simulations in 3ds Max using V-Ray. Chapter 2 assumes you read the first chapter and provides a quick overview of the process of setting up a custom Color field in Houdini which is then exported as VDB and used as the shading color for the smoke simulation.
You can download the assets for this chapter from the button below:
Setup in Houdini
The provided .hip file contains a sphere with animated noise. The Cd SOP field is populated using a Color Ramp sampled based on the current Time value. A few DOP nodes are used to add additional detail in the vel field, and the Cd DOP field is generated by the Vector Field DOP called "create_Cd_field".
As this is not a Houdini tutorial, if anything going on in this setup is unclear, please refer to the Houdini Documentation. The nodes in the .hip file are named descriptively, so a quick glance over the network should clarify things. Other good and free sources of information are Tokeru's Website, as well as the SideFX and OdForce forums.
Setup in 3Ds Max
In 3ds Max, create a V-Ray Volume Grid and point the Preview & Render Cache Path to the Houdini VDB files.
Open the 3rd Party Channel Mappings dialog by clicking the "..." button and set the Red / Green / Blue channels to Cd.x / Cd.y / Cd.z if they aren't populated already.
Cd.* are the names of the Houdini fields in the cache file. The Red/Green/Blue channels are the Phoenix FD equivalents that are already set up for you.
Go to the bottom of the Preview rollout and enable the GPU Preview.
Then, in the Rendering rollout, click on the Volumetric Options button, go to the Smoke Color rollout and set the Based on parameter to RGB.
That's it. The Smoke channel is now shaded based on the RGB channel which, in turn, points to the Cd.* fields in the VDB cache.
No additional set up is required and you may render to view your result.
If the Smoke appears white instead of colored, as it does in the screenshot to the right, this is most likely caused by the Intensity of the lights in your scene. The GPU Preview is not as good as a render, so make sure to render and see how the final result will look before changing anything.
If the Smoke appears completely black, a possible reason could be that you've reloaded the Cache files or pointed the Preview & Render Path to another sequence, and the remapping from the 3rd Party Channels Mappings is broken.
Optionally, you can further adjust the settings in the Smoke Opacity rollout, in case you like to give the smoke a thinner or thicker appearance.
Here is the final result: