In this brief tutorial we will examine one of WorldBuilder’s coolest features. It allows you to render realistic 3D clouds, usually referred to as Cumulonimbus. These are different from the clouds found in the Compound Sky element.
Note: This tutorial is designed to be used with the free downloadable Demo version of WorldBuilder 4. Certain features in this version have been disabled, such as file and image saving. Likewise, the Demo version does not allow you to create animations. For this reason, example scene files and animations are available for you to download and compare to the results obtained in this tutorial.
Click on the Cumulonimbus Clouds button in the Creation toolbar.
A bounding-box object will appear in the Viewports.
Because of the way the cloud object is rendered, it cannot be displayed in real-time except in bounding box mode.
Select the cloud’s properties.
The first of these is Cloud Shape.
The first set of parameters in ‘Cloud Shape’ is the Voxel Number settings. These are the spatial dimensions of the Cumulonimbus cloud, where X = width, Y = depth and Z = Height.
The range, for each of these settings, starts at 10 and has a maximum value of 100.
Note: A voxel (‘volumetric pixel’ ) is a special kind of object used for rendering cloudy or gaseous materials.
Below Voxel Number there is a Random Seed control. This varies the distribution of the voxels throughout the cloud’ s volume. Try clicking on the up or down scroll arrows, to change the seed value.
Render the results.
You can also play with different parameter combinations for Spheres Number. This property sets the number of spheres that contribute to the cloud’ s ‘density of detail’ ; a low Spheres value makes a very smooth cloud, while a higher Spheres value produces more ‘puffy’ details in the cloud.
Let’ s look at a few rendered Spheres Number variations:
Spheres Number = 1
Spheres Number = 50
Spheres Number = 500
A sub-property of Cloud Shape is Cloud Profile. This is a graphical interface for editing your cloud’ s profile, represented here as a spline curve with movable points. Click and drag on the points to alter the cloud’ s shape.
Double-click to add a new point to the profile curve; right-click to delete a point. Try out a few combinations to see what kinds of cloud shapes you can make.
Here are some rendered examples.
Now that we’ ve made some adjustments to the shape of our cloud, let’ s explore our shading options. In the Properties Tree, select Cloud Shader.
First in the Cloud Shader property is Extinction. Use this to control the cloud’ s transparency. A high setting will make the cloud very solid and opaque, while a low setting will make the cloud more wispy and ‘fog-like’ .The practical range for this control is roughly between 1 (almost completely transparent) to 10 (above which increasing opacity values are not as noticeable); a good starting value is the default setting of 3.
Let’ s render a couple of different Extinction settings.
Extinction = 1.25
Extinction = 2
Extinction = 6
The Intensity parameter controls the cloud’ s responsiveness to a light source. Low settings cause the cloud to render very dim and very flat; a high setting will cause the directly illuminated areas of the cloud to become so bright that shadowed areas of the cloud will be obscured.
Intesity = 2.5
Intesity = 10
Intesity = 20
The Asymmetry parameter controls the scattering of light within the cloud’ s volume. A low setting (0.1 or lower) will cause the light to scatter ‘isotropically’ (equally in all directions) within the cloud, which will appear darker; a higher setting will cause the light to scatter in a more uniform direction, creating brighter areas within the cloud.
Asymmetry = -0.8
Asymmetry = -0.1
Asymmetry = 0.4
Albedo controls the overall contrast between the brighter, directly illuminated areas of the cloud and the darker shadowed areas.
Aibedo = 0.23
Aibedo = 0.45
Aibedo = 1.8
Cloud Shader also includes two controls for setting cloud color.
Cloud Color shades the cloud areas which are directly illuminated.
Ambient Color controls the shading for the darker parts of the cloud (that is to say, the parts of the cloud in shadow or indirectly illuminated). It’ s important to keep in mind that Ambient is the ‘base’ color’ for the cloud; if the Ambient Color is brighter than the Cloud Color, the cloud will be brighter overall.
Here are a few different combinations of Cloud and Ambient Color.
Finally, let’ s apply a useful sub-property of Cloud Shader: Select Light Sources.
This control allows you to simulate certain kinds of lighting phenomena which can occur when a cumulonimbus cloud is receiving reflected or ‘bounced’ light from the ground, or from another cloud.
Add a new Parallel Light to the scene. Move the light’ s target so that it is inside or above the cloud. Basically, we want the new light pointing up at the cloud from below (be sure, however, not to place the light beneath the landscape!).
The Asymmetry parameter controls the scattering of light within the cloud’ s volume. A low setting (0.1 or lower) will cause the light to scatter ‘isotropically’ (equally in all directions) within the cloud, which will appear darker; a higher setting will cause the light to scatter in a more uniform direction, creating brighter areas within the cloud.
Reduce the light’ s intensity and use the Color button to pick a green hue. You can even use the Color Picker’ s eyedropper cursor to directly select the green from the rendered image.
Now click on the Cumulonimbus0 object, and select the Select Light Sources property. The original light source, Parallel_Light_0, should already be highlighted. Now Ctrl+click on Parallel_Light_1 to add that light to the selection.
Note: Only Parallel Lights are supported by the Select Light Sources property. Spot and Point lights -even if they are added to the scene- will not appear in the selection window.
Render the scene again. Now our cloud has a subtle, more realistic ‘bounce light’ effect visible on its underside.
Here are a few other variations making use of the Select Light Sources property.
This concludes our brief Cumulonimbus tutorial. We hope you found it useful and interesting.
Watch our website for future tutorials exploring Digital Element’ s line of virtual nature products.