Increasing the Map Size value slows rendering.
Volume effects are used to create clouds, fog, smoke, beams of light, halos, and many other effects that add a sense of realism, drama, or fantasy to a scene.
You can produce a volume effect with either a volumic property (see Creating a Volumic Light Property) or a volume shader. Volume shaders modify rays as they pass through an object (see Creating Volume Effects with an Object) or the scene as a whole (see Creating a Volume Effect in a Scene).
Creating a Volumic Light Property
You can create volumic lights using volume shaders, but a simpler method is to apply a volumic property to your light. The volumic property is also applied at the scene level and it can be easily activated to create simple scene atmospherics (as described in Creating Depth Fading).
To create a volumic light property
1. Select an existing light or create a new one (Get > Primitive > light).
2. Make sure the light shader (soft_light by default) has Light Attenuation > Light Falloff enabled.
3. From the Render toolbar, choose Get > Property > Volumic. The Volumic Light Property Editor opens.
4. On the Volumic tab, the principle parameter to edit when defining a volumic light is Map Size, which determines the depth map resolution of the effect.
If the objects the volumic light is crossing are simple, the map volume can be set very low (100 to 200). But if the objects in the light’s path are complex, such as very sharp edges, you need to increase the Map Size value to pick up more of the object’s shape detail, creating a better volumic effect.
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Increasing the Map Size value slows rendering. |
5. Adjust the Reflectance parameter to simulate the volume’s reflectivity. A low value (0.5) simulates a volumic effect with low reflectivity, such as dust. A higher value (greater than 2) creates a reflective volume, such as dense smoke.
6. You can set the distance from the light source at which the volumic effect begins by using the Min Distance slider.
7. Select Force Volume Shadows to force the rendering of shadows for the volumic effect.
- When this option is off, volumic lights appear to go through objects.
- When this option is on, objects occlude volumic lights and cause shadows.
8. To make the volumic effect have a transparent quality, select Transparent.
9. On the Shards tab, set the volumic light’s shard parameters. They are off by default. You can activate shards, set their intensity, complexity, and resolution.
Creating a Volume Effect in a Scene
Volume shaders modify rays as they pass through an object (see Creating Volume Effects with an Object) or the scene as a whole. When you apply a volume shader to a render pass, it surrounds the scene rather than being bound to a single object.
To create a volumic scene effect
1. Select the pass to which you will apply the volume shader and open its Render Pass Property Editor.
2. Click the Pass Shaders tab.
3. In the Volume stack window, click Add to select a volume shader from the shader library. See Volume Shaders [Shader Reference].
4. Click OK when you have chosen a shader—it appears in the shader stack list.
5. Select the shader in the Volume stack window and click Inspect. This opens the shader’s property editor. For more information on how to use a particular volume shader, click the 
icon in the shader’s property editor.
Creating Volume Effects with an Object
Volume shaders modify rays as they pass through an object or the scene as a whole (see Creating a Volume Effect in a Scene). You can use a geometric object to constrain or “hold” a volume effect within a specific region. Usually the object is fully transparent so that you can see the volumic effect.
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The volume smoke effect is “held” within the confines of a fully transparent object. A scatter light was placed within the bounding volume to illuminate and shadow the smoke particles. See Volume Effects [Shader Reference]. |
To create an object-based volume effect
1. Select an object to which you want to apply a volumic effect.
When you have a volumic effect assigned to a bounding box–type object (for example, a sphere or cube to hold a fog effect), make the geometric object as small and as simple as the scene allows. Since the object is not (usually) rendered or visible, bring down its subdivisions and scale it as small as possible for the scene or the effect the object is holding.
This does not apply, of course, if the object is an integral part of the effect you are trying to achieve and you want the volume effect to closely follow or “honor” the shape of the object that contains it (as illustrated above).
2. From the Render toolbar, choose Get > Shader > Volume and select from the list of available shaders. See Volume Shaders [Shader Reference].
3. Once you select a shader, it is attached to the Volume input of the object’s material node (see the render tree example below) and its property editor opens.
4. You can edit the volume effect’s parameters. For more information on parameters for a particular volume shader, click the 
button in the shader’s property editor.
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