The natural consequence of a volumetric material is (quite obviously) clouds.
A simple way to create clouds in Cycles is by modeling the desired shape and then assigning an appropriate volumetric material. In the following screenshot, you can see this method applied to the usual Suzanne mesh:
The volumetric Suzanne cloud as it appears in the final rendering
Start Blender and open the 9931OS_09_cloud_start.blend file, where there is the Suzanne_cloud object with two Emitter mesh-lights and a bright World set with a Sky Texture.
- Go to the Object modifiers window and raise the Subdivisions level of the Subdivision Surface modifier from
2to3for both Preview and Render. - Assign a new Subdivision Surface modifier. Set the Subdivisions level to
2. - Assign a Displace modifier. Click on the Show texture in texture tab button to the right of the New button to switch to the Texture window.
- Click on the New button under the Displace item, then click on the Type slot to switch from Image or Movie to Clouds. Set the Size to
0.35and the Depth to3. - Go back to the Object modifiers window and click on the Vertex Group slot to select the rest item. Then set the Strength value to
0.400.
The displaced Suzanne cloud seen in the Solid Viewport Shading mode and the assigned modifiers in the main properties panel to the right
After creating the cloud shape, let's make a start on the material:
- Ensure that the Suzanne_cloud object is still selected, and click on the New button in the Node Editor toolbar or in the Material window under the main Properties panel.
- In the Node Editor window, select and delete the Diffuse BSDF shader node.
- Add a Volume Scatter node (press Shift + A and navigate to Shader | Volume Scatter), a Volume Absorption node (press Shift + A and navigate to Shader | Volume Absorption), and an Add Shader node (press Shift + A and navigate to Shader | Add Shader).
- Connect the output of the Volume Absorption node to the first Shader input socket of the Add Shader node, and the Volume Scatter output to the second Shader input socket. Connect the output of the Add Shader node to the Volume input socket of the Material Output node.
- Add a Mix Shader node (press Shift + A and navigate to Shader | Mix Shader) and paste it between the Add Shader node and the Material Output node. Connect the output of the Volume Scatter node to the second Shader input socket of the Mix Shader node. Set the Fac value to
0.700. - Add a Value node (press Shift + A and navigate to Input | Value) and an RGB node (press Shift + A and navigate to Input | RGB). Connect the Value output to both the Density input sockets of the Volume Absorption and Volume Scatter nodes. Set the input value to
5.000. - Connect the output of the RGB node to the Color input sockets of the Volume Absorption and Volume Scatter nodes. Set the color values for R to
0.890, G to0.866, and B to0.832. - Under the Material windows, go to the Settings subpanel and enable the Homogeneous item.
- Go to the Scene window, and under the Color Management subpanel, enable the Use Curves item. Then click on the curves window to create a new control point. Set its coordinates as X to
0.67206and Y to0.88125. Click again to create a new control point, and set the coordinates as X to0.31579and Y to0.46875. Have a look at the following screenshot:
The Rendered preview of the Suzanne cloud and the material network in the Node Editor window
Most of the effect of this material is because of the Displace modifier deforming the Suzanne mesh in order to resemble the shape of a Suzanne cloud. The material itself is simply a combination of the Volume Scatter and the Volume Absorption shader, first added by the Add Shader node and then with a Mix Shader node to further control the mixing of the scattering in the whole shader.
The Vertex Group, rest, selected in the Displace modifier slot is simply a group with lower weight going towards the ears, because they are quite thin, and the displacement we're using can easily cause bad mesh intersections.
The Rest Vertex Group visible in the Weight Paint mode
In the last step, we enabled curves for the Color Management to obtain a brighter and more contrasted rendering of the cloud against the sky.