Very briefly (because there are dedicated recipes in the last chapter of this Cookbook), let's take a look at how volumetric materials work in Cycles.
Volumetric materials are exactly what they sound like. Instead of the surface of an object, Cycles renders the inner volume of that object, and this gives space to a lot of interesting possibilities—not only can elusive materials such as smoke, fire, clouds, or light transmission effects through the medium be realized, but peculiar shapes can also be obtained from the volume itself by Boolean operations made through material nodes.
The drawback is that volume materials are slow—a lot slower compared to the surface materials, but hopefully, this is an issue that will be fixed in some way in the future (be aware that from Version 2.72, volume materials are available on GPUs too).
Let's start with our usual Spheroid blend file:
start_02.blend
file and delete the material assigned to the Spheroid.Now let's go to the volume section of the Material window with the following steps:
1.000
to 50.000
. The Spheroid looks a lot more solid now, as shown in the following screenshot:3.800
.0.100
.50.000
. Here is a screenshot of the output of a Voronoi Texture node for your reference:0.800
, 0.214
, and 0.043
, respectively.01_volumetric.blend
.We have seen that when we increase the Density value of the Volume Scatter node, the Spheroid starts to look more and more solid. So, we used the output of a Voronoi Texture node and clamped it with a Less Than node to show only the values that are not beyond the 0.100
limit. Then we multiplied the value by 50.000
, thus increasing the density of the Voronoi spheres and making them appear as solid objects inside the Spheroid volume.
Remember that in this case, we rendered only the inside of the object and not the surface. Anyway, a combination of Surface and Volume is possible and can give interesting results, as shown in the following screenshot:
Volumes also work in the World. In fact, the World Output node now has a Volume input socket. By connecting a Volume Scatter or Volume Absorption node to the World Output node, it is possible to obtain several special effects, for example, fog, mist, atmospheric perspective, atmospheric scattering effects, and a body of water for an underwater scene. Clearly, it's also possible to fill this environment volume with textures.
In any case, you won't usually fill the entire World with a volumetric material because the World in Blender is considered as going to an infinite distance, and this would make the volume calculation too heavy. It's better to use a scaled Cube, properly placed and filled with the volume material.
To know more about volume materials, go to the last chapter of this Cookbook or to the documentation on the wiki at http://wiki.blender.org/index.php/Doc:2.6/Manual/Render/Cycles/Materials/Volume.
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