This page provides information about Fog and Environment Fog creation in V-Ray for Houdini.
Creating a fog in Houdini could be done with all available volume Houdini tools. As V-Ray is still in beta stage and does not support native Houdini volumes, there is a simple workaround to help us create and work with Houdini volumetrics. For the goal, we will export them with VDB and then load them in V-Ray Volume Grid.
To download the files used in this tutorial, please click on the button below.
Let's create a box and dive into its node. Change the size number to something big enough to cover the scene.
Create a VDB from Polygons. Disable the Distance VDB and enable the Fog VDB instead.
In order to reduce the density of the generated fog, we use the Volume Wrangle. Use a VEXpression as so: @density = .2;
With this step, the creation of the fog is completed. Additionally, we can use all Houdini tools to customize the fog.
V-Ray Beta 1 does not support the native Houdini Volumes yet. So, the next step is to save the fog as VDB using the ROP Output Driver SOP.
Then, we import it back through V-Ray Volume Grid Cache SOP (TAB Menu > V-Ray > V-Ray Volume Grid Cache).
Now, in the viewport we should see the loaded VDB volume.
Our next step is to create a Material Network and dive into it in order to do a fog shader.
Create a Volume Grid Shader (TAB Menu > V-Ray > Volume > Volume Grid Shader).
Go to the Fire tab and set Based on to Disabled. We disable it since we do not have any fire in the scene.
Go to the Smoke tab.
In the Color group, set Based on to Constant Color. We set the color to white. You can play with the fog color, but since the fog we do here is almost transparent, white is good enough.
In the Opacity group, set Based on to Simple Smoke. Change the Simple Smoke Opacity to 0.01, but the Min. Visible Opacity stays unchanged.
In general, if the Simple Smoke Opacity is too low, the Min. Visible Opacity can be changed, but in our case there is no need.
In the fog container, we put two test objects and two separate lights, so that the fog effect is easily distinguishable. Create a camera, too.
And here is the rendered result.