In this tutorial, we will go through how to setup and use the Volume Sample Float shader to adjust the color temperature effect of an OpenVDB file.
A tutorial on how to write volumes to OpenVDB from Houdini can be found here.
- Start off by downloading a VDB file such as the explosion.vdb or fire.vbd file, for example, from the OpenVDB download page.
- Create an Arnold Volume - Plugins > C4DtoA > Arnold Volume.
Select the .vdb volume in the File path attribute.
- Create a Point light and position it outside of the volume.
- Create a Standard Volume shader - Arnold > Volume > standard_volume in the Material Manager
- Assign the Standard Volume shader to the Volume.
We can use a Volume Sample Float shader to control the appearance of the fire volume effect. This shader will remap the values of the 3D voxel grid in the same manner as tone-mapping and remapping filters to an image in Photoshop, which operates in a 2D grid.
- Open the shader network editor of the Standard Volume shader.
- Create a Volume Sample Float shader. Connect it to the Density parameter of the Standard Volume shader.
- Set density to the Volume Sample Float channel.
- Remove density from the Standard Volume Density channel.
- Set Emission of the Standard Volume to channel and use density as the Channel. This will give us the fire.
We can use the Volume Sample Float shader to alter the appearance of the smoke and fire. The following images show different adjustment attributes and their effect on the volume.